Biodiversity of vibrios

Allelic variations and gene cluster modularity act as nonlinear bottlenecks for cholera emergence

The underlying factors that lead to specific strains within a species to emerge as human pathogens remain mostly enigmatic. The diarrheal disease cholera is caused by strains from a phylogenetically confined group within the Vibrio cholerae species, the pandemic cholera group (PCG), making it an ideal model system to tackle this puzzling phenomenon. Comprehensive analyses of over 1,840 V. cholerae genomes, including environmental isolates from this study, reveal that the species consists of eleven groups, with the PCG belonging to the largest and located within a lineage shared with environmental strains. This hierarchical classification provided us with a framework to unravel the ecoevolutionary dynamics of the genetic determinants associated with the emergence of toxigenic V. cholerae. Our analyses indicate that this phenomenon is largely dependent on the acquisition of unique modular gene clusters and allelic variations that confer a competitive advantage during intestinal colonization. We determined that certain PCG-associated alleles are essential for successful colonization whereas others provide a nonlinear competitive advantage, acting as a critical bottleneck that clarifies the isolated emergence of PCG. For instance, toxigenic strains encoding non-PCG alleles of a) tcpF or b) a sextuple allelic exchange mutant for genes tcpA, toxT, VC0176, VC1791, rfbT, and ompU, lose their ability to colonize the intestine. Interestingly, these alleles do not play a role in the colonization of newly established model environmental reservoirs. Our study uncovers the evolutionary roots of toxigenic V. cholerae offering a tractable approach for investigating the emergence of pathogenic clones within an environmental population.

Research on the histopathology of Larimichthys crocea affected by white gill disease and analysis of its bacterial and viral community characteristics

White gill disease (WGD) is one of the major diseases affecting Larimichthys crocea, although its etiology remains unclear. To investigate the causes of WGD, this study selected WGD-affected Larimichthys crocea (WG) and healthy Larimichthys crocea (NH) from multiple aquaculture regions for pathological analysis and analysis of bacterial and viral community characteristics. The results indicated severe tissue damage and significant inflammatory responses, as evidenced by clinical manifestations and electron microscopy. Two bacterial species, Photobacterium damselae and Vibrio campbellii, were isolated from all lesion tissues. Additionally, 16S full-length sequencing results showed that Photobacterium damselae and Vibrio campbellii dominated in the tissues of Larimichthys crocea, with a combined relative abundance of approximately 90 %. There were no significant differences in α-diversity and β-diversity between the NH group and WG group from the three aquaculture regions, and no significant biomarkers were identified. The diversity of DNA and RNA viruses did not show significant differences between the NH and WG groups, although both types of viruses exhibited notable synergistic and antagonistic relationships. Analyses from 16S full-length sequencing, metagenomics, and metatranscriptomics revealed that the related functional genes were primarily enriched in various metabolic pathways, including glycine biosynthesis, membrane transport, and energy metabolism. The metatranscriptomic analysis indicated that the expression levels of genes related to antibiotic resistance, biosynthesis, transport, and degradation processes were significantly downregulated in the WG group. Finally, through PCR, qPCR, and metagenomic sequencing, we were unable to detect iridovirus in Larimichthys crocea, further suggesting that the causes of WGD may differ across aquaculture regions compared to previous reports. This study indicates that the etiology of WGD may involve complex ecological and metabolic mechanisms, rather than being merely the result of a single pathogen infection. This research provides a comprehensive analysis of the microbial communities in WGD-affected Larimichthys crocea from multiple aquaculture regions for the first time, providing a theoretical basis for further elucidating the causes of WGD and developing preventive measures.

Integrated Vibrio load variation and transcriptome profiles provide new insights into the defensive response of Cyclina sinensis under Vibrio parahaemolyticus infection

Vibrio parahaemolyticus is the dominant pathogen in mariculture, leading to the bivalves' mass summer mortality. This study investigated the antibacterial defense mechanism of the Cyclina sinensis against V. parahaemolyticus. The immersion challenge revealed that the daily mortality of C. sinensis increased and then decreased gradually, and the mass mortality occurred about a week after V. parahaemolyticus infection. The Vibrio load in the hepatopancreas of C. sinensis was dramatically increased at 12-24 hpi (hours post-infection) and then declined significantly at 2-7 dpi (days post-infection). RNA-Seq generated 866 differentially expressed genes (DEGs), and KEGG analyses enriched multiple innate immune-related and metabolic-related pathways. The expression levels of nine immune-related and metabolic-related DEGs were significantly changed after Vibrio infection, and their temporal expression patterns were multiple. Our results indicated that the immunity and metabolic responses might be reprogrammed to protect the host against pathogens at the early infection phase. This study would expand our knowledge of the pathogenesis mechanisms of clams infected with Vibrio and provide a theoretical basis for healthy shellfish cultivation.

Genomic Repertoire of Twenty-Two Novel Vibrionaceae Species Isolated from Marine Sediments

The genomic repertoire of vibrios has been extensively studied, particularly regarding their metabolic plasticity, symbiotic interactions, and resistance mechanisms to environmental stressors. However, little is known about the genomic diversity and adaptations of vibrios inhabiting deep-sea marine sediments. In this study, we investigated the genomic diversity of vibrios isolated from deep-sea core sediments collected using a manned submersible off Japan. A total of 50 vibrio isolates were obtained and characterized phenotypically, and by genome sequencing. From this total, we disclosed 22 novel species examining genome-to-genome distance, average amino acid identity, and phenotypes (Alivibrio: 1; Enterovibrio: 1; Photobacterium: 8; Vibrio: 12). The novel species have fallen within known clades (e.g., Fisheri, Enterovibrio, Profundum, and Splendidus) and novel clades (JAMM0721, JAMM0388, JAMM0395). The 28 remainder isolates were identified as known species: Aliivibrio sifiae (2), A. salmonicida (1), Enterovibrio baiacu (1), E. norvegicus (1), Photobacterium profundum (3), P. angustum (1), P. chitiniliticum (1), P. frigidiphilum (1), Photobacterium indicum (1), P. sanguinicancri (1). P. swingsii (2), Vibrio alginolyticus (3), V. anguillarum (1), V. campbellii (1), V. fluvialis (1), V. gigantis (1), V. lentus (1), V. splendidus (4), and V. tasmaniensis (1). Genomic analyses revealed that all 50 vibrios harbored genes associated with high-pressure adaptation, including sensor kinases, chaperones, autoinducer-2 (AI-2) signaling, oxidative damage repair, polyunsaturated fatty acid biosynthesis, and stress response mechanisms related to periplasmic and outer membrane protein misfolding under heat shock and osmotic stress. Additionally, alternative sigma factors, trimethylamine oxide (TMAO) respiration, and osmoprotectant acquisition pathways were identified, further supporting their ability to thrive in deep-sea environments. Notably, the genomes exhibited a high prevalence of antibiotic resistance genes, with antibiotic efflux pumps being the most abundant group. The ugd gene expanded in number in some novel species (Photobacterium satsumensis sp. nov. JAMM1754: 4 copies; Vibrio makurazakiensis sp. nov. JAMM1826: 3 copies). This gene may confer antibiotic (polymyxin) resistance to these vibrios.

Photoproduction of Acetaldehyde from Bacteria-Derived Dissolved Organic Matter

We explored the photoproduction of oxygenated volatile organic compounds (OVOCs) from marine bacteria-derived dissolved organic matter (B-DOM). B-DOM was obtained from the growth phase to the stationary phase in a culture experiment with marine bacteria in coastal seawater. B-DOM composition was evaluated through chromophoric dissolved organic matter (CDOM) and fluorescent dissolved organic matter (FDOM) (e.g., amino acid-like, humic-like). Photoproduced OVOCs from B-DOM were measured using Proton Transfer Reaction Time of Flight Mass Spectrometer (PTR-ToF-MS). Acetaldehyde was photoproduced from B-DOM in proportion to light exposure time, with photoproduction rates of 0.20-0.51 nM h-1. However, no direct quantitative relationship between the acetaldehyde photoproduction rates and the levels of CDOM or FDOM was observed. Since acetaldehyde photoproduction was highest during the growth phase of the bacterial culture, it was suggested that the fraction of B-DOM susceptible to microbial degradation contributes to the source of acetaldehyde. In contrast, the photoproduction of acetone from B-DOM was minimal, implying sources other than B-DOM are responsible for acetone on the marine surface. These findings suggest that B-DOM has the potential to generate acetaldehyde upon solar exposure, with implications for understanding the contribution of microbial-derived organic matter to the production of these compounds in the marine environment.

Distribution, Antibiotic Resistance, and Virulence Factors of Vibrio parahaemolyticus in the Southern Coastal Waters of Republic of Korea

Background/Objectives:Vibrio parahaemolyticus is a marine bacterium and a major cause of food poisoning worldwide, primarily associated with gastric illnesses such as gastroenteritis. This study aimed to investigate the distribution, antibiotic resistance, and virulence genes of V. parahaemolyticus present in shellfish and seawater of the southern coast of Korea, a major shellfish harvesting area. Methods: Shellfish and seawater samples were collected monthly in 2023 from 24 coastal sites in Korea. V. parahaemolyticus was isolated and identified using the MPN method, biochemical tests, MALDI-TOF mass spectrometry, and 16S rRNA sequencing. Antimicrobial susceptibility was tested for 673 isolates using the Sensititre MIC system, and virulence genes (tdh and trh) were detected by PCR. Results:V. parahaemolyticus had a detection rate of 18.2-58.3% in shellfish and 8.3-50% in seawater samples. Among the isolates, 97.9% and 97.3% were resistant to ampicillin and colistin, respectively, while 8.3% showed resistance to four or more antibiotics. The virulence genes tdh and trh were detected in 0.45% and 3.34% of shellfish samples and 1.23% and 4.46% of seawater samples, respectively. Conclusions: These findings will help implement appropriate precautionary measures to prevent potential human health risks arising from exposure to multidrug-resistant or pathogenic V. parahaemolyticus.

Effect of intestinal microbiota on adaptation to overcrowding stress in grouper (Epinephelus fuscoguttatus♀×E. lanceolatus♂)

Density is an important aquaculture parameter. When the pearl gentian grouper (Epinephelus fuscoguttatus♀ × E. lanceolatus♂) is farmed intensively, it could lead to a degradation in genetic resources and an increase in disease outbreaks. The composition of the intestinal microbiota plays a key role in creating a specific intestinal microecosystem, which is essential for the survival, growth, and immune response of the host under environmental stress like overcrowding. This study utilized 16S rRNA sequencing and metabolomics analysis techniques to investigate the differences in intestinal microbial community stability of grouper under different stocking time and density pressure conditions. The research results showed that compared to the low-density group, the high-density group of groupers experienced an increase in mortality rate and feed coefficient in the early stages of culture, while the weight gain rate decreased. Differential analysis of intestinal microbial communities revealed significant differences in the gut microbiota of grouper between different density groups after 10 days of culture, but no significant differences were observed after 20 days of culture. At the same time, intestinal histopathology showed that the high-density group of groupers exhibited a reduction in intestinal villi length and thickness of the intestinal wall after 10 days of culture. However, the intergroup differences had reduced after 20 days of culture. Furthermore, high density cultivation upregulated the expression of inflammatory factors like IL-1β, TNF-α, IL-8, and IL-6 in the intestinal tract of groupers after 10 days of culture. However, after 20 days of culture, the expression levels of intestinal inflammatory factors in both the high-density and low-density groups of groupers were significantly reduced, and the differences between the intergroup diminished. Through correlation analysis of differential metabolites and species in the intestine, multiple metabolites significantly upregulated and associated with the upregulation of the Staphylococcus genus were identified in the intestinal tract of groupers after 20 days of high-density cultivation. The selected four associated metabolites (including creatine, fosinopril, 4-aminobutyric acid, and guanidinopropanoic acid) were validated to significantly reduce the expression of cellular inflammatory factors using the self-established grouper head kidney (HK) cell line. In conclusion, density pressure in the early culture period could affect the stability of the intestinal microbial environment of grouper. As aquaculture time increases, the intestinal microbial community of grouper drives the body's anti-inflammatory response and enhanced its adaptation to density pressure by regulating own structure and secretion of metabolites.

Isolation, complete characterization and phylogeography of the first bacteriophage against Vibrio neocaledonicus, which encodes a pyruvate phosphate dikinase and represents a novel viral family

Vibrio are widely distributed in aquatic environments and are major pathogens commonly found in aquaculture environments, playing a significant role in human production activities and maintaining ecological stability. Here, a novel phage, vB_VneS_J26, which infects Vibrio neocaledonicus, was isolated from coastal seawater in Qingdao, China. Transmission electron microscopy revealed that vB_VneS_J26 exhibits siphovirus morphotype, with a linear double-stranded DNA genome of 82,477 bp in length and G+C content of 45.11 mol%, encoding 122 putative ORFs. Three auxiliary metabolic genes related to carbon metabolism and host cell redox processes were identified, including a pyruvate phosphate dikinase, which catalyses the reversible conversion between phosphoenolpyruvate and pyruvate and is rarely detected in viruses. Whole-genome phylogenetic and comparative genomic analyses suggested that vB_VneS_J26 represents a potential novel viral family, comprising six isolated vibriophages, proposed as Modirecodeviridae. Phylogeographic analysis indicated that Modirecodeviridae is primarily distributed in epipelagic and mesopelagic zones of the Arctic and temperate tropical oceans.

Pathogenic mechanisms of Enterocytozoon hepatopenaei through the parasite-gut microbiome-shrimp ( Litopenaeus vannamei) physiology axis

The progressive impact of Enterocytozoon hepatopenaei (EHP) infection on gut microbial function in Litopenaeus vannamei remains poorly understood beyond static comparisons between healthy and infected individuals. To close this knowledge gap, metagenomic sequencing was used to characterize the gut microbiomes of normal, long, medium, and short-sized adult shrimp categorized by increasing severity of infection. EHP infection suppressed digestive activity while inducing immune responses compared with healthy shrimp. Increasing infection severity was associated with a gradual decline in gut α-diversity and an expansion of potential pathogens and virulence factors (VFs). In addition, dysbiosis in gut microbiota composition and function, as well as reduced network stability among differential species, intensified with infection severity. Accordingly, we identified 24 EHP-discriminatory species that contributed an overall 83.3% accuracy in diagnosing infection severity without false negatives. Functional pathway analysis revealed significant suppression of metabolic, degradative, and biosynthetic processes in EHP-infected shrimp compared with healthy controls. Among them, map00630 glyoxylate and dicarboxylate metabolism and map00280 valine, leucine and isoleucine degradation were consistently depleted in infected individuals, thereby impairing their digestive function and anti-inflammatory responses. Additionally, EHP infection diversified VFs directly affecting shrimp gut microbiome. These findings support a conceptual model linking EHP pathogenesis to the parasite-gut microbiome-shrimp physiology axis.

A comparative genomic analysis at the chromosomal-level reveals evolutionary patterns of aphid chromosomes

Genomic rearrangements are primary drivers of evolution, promoting biodiversity. Aphids, an agricultural pest with high species diversity, exhibit rapid chromosomal evolution and diverse karyotypes. These variations have been attributed to their unique holocentric chromosomes and parthenogenesis, though this hypothesis has faced scrutiny. In this study, we generated a chromosomal-level reference genome assembly of the celery aphid (Semiaphis heraclei) and conducted comparative genomic analysis, revealing varying chromosomal evolution rates among aphid lineages, positively correlating with species diversity. Aphid X chromosomes have undergone frequent intra-chromosomal recombination, while autosomes show accelerated inter-chromosomal recombination. Moreover, considering both inter- and intra-chromosomal rearrangements, the increased autosomal rearrangement rates may be common across the Aphidomorpha. We identified that the expansion of DNA transposable elements and short interspersed nuclear elements (SINEs), coupled with gene loss and duplication associated with karyotypic instability (such as RIF1, BRD8, DMC1, and TERT), may play crucial roles in aphid chromosomal evolution. Additionally, our analysis revealed that the mutation and expansion of detoxification gene families in S. heraclei may be a key factor in adapting to host plant chemical defenses. Our results provide new insights into chromosomal evolutionary patterns and detoxification gene families evolution in aphids, aiding the understanding of species diversity and adaptive evolution.

Global systematic mapping of Vibrio species pathogenicity: A PRISMA-guided cluster-based analysis

BACKGROUND

A systematic global map on toxigenesis and genomic virulence of Vibrio spp. was analyzed for research progress to identify the emerging research patterns for establishing a database for designing future interventions.

METHOD

The databases (Web of Science and Scopus) were analyzed with Voxviewer software to map the global scale of Vibrio spp. or virulence toxin/genes publications and standardized using Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) strategies.

RESULTS

The results identified 1162 (Web of Science n = 620, Scopus n = 542), while 314 studies qualified for inclusion and were significantly analyzed on virulence toxin/genes. By co-citation analysis, 4-thematic clusters were developed from 6420 citations and a total reference of 9062. Cluster #1 (pathogenesis & virulence factors) and cluster #4 (host response factors) generated the utmost publications and citations (n = 40, 643) and the least (n = 7, 85) interest by the researcher. Whereas 8-thematic clusters were developed by bibliographic coupling technique analysis, cluster#1 and cluster#8 generated the utmost (n = 78, 1684) and least (n = 7, 81) publications and citations interest by the researcher.

CONCLUSIONS

Our findings suggest that Vibrio toxigenesis and virulence factors are a complex field requiring an interdisciplinary approach consisting of interconnected perspectives that have important consequences for academics and policymakers.

Temporal and spatial co-occurrence of pacific oyster mortality and increased planktonic Vibrio abundance

Oyster mortality and human food poisoning events are linked to pathogens from the Vibrio genus. However, the link between these events, planktonic bacterial dynamics and environmental variables has not yet been resolved. In Port Stephens, Australia, we characterized the microbial community and quantified the abundance of total Vibrio, Vibrio harveyi, and Vibrio parahaemolyticus in a (i) 27-month seawater planktonic microbial time-series; (ii) samples of Pacific oysters (Crassostrea gigas) during a mortality event and (iii) seawater samples following the mortality event. Vibrio harveyi and V. parahaemolyticus exhibited seasonal abundance, peaking during the summer months. Total Vibrio and V. harveyi in seawater were significantly greater at sites with high levels of oyster mortality and decreased 5-fold in the weeks following oyster mortality. Our findings provide evidence for the role of Vibrio in oyster mortality events and indicate that ocean warming and elevated phytoplankton may stimulate putative pathogens in the Vibrio genus.

Non-toxigenic Vibrio cholerae - just another cause of vibriosis or a potential new pandemic?

Although nontoxigenic Vibrio cholerae usually stands in the shadow of the two serogroups (O1 and O139) that cause pandemic cholera, its role in human pathology is increasingly recognized and described in the literature. The habitat of these pathogens is brackish seawater or even freshwater, and the infections caused by them include contact with these waters or consumption of seafood originating in this habitat, which is constantly expanding because of global warming. This habitat extension is a typical example of climate change's impact on infectious diseases. Although nontoxigenic Vibrio cholerae strains are rarely capable of producing the classical cholera toxin, they possess many other virulence factors, can secrete various other toxins, and thus produce illnesses that are sometimes even severe or life-threatening, more frequently in immunocompromised patients. Vibriosis may manifest as gastrointestinal illnesses, wounds, skin or subcutaneous tissue infections, or septicemia. To establish the correct etiological diagnosis for these infections, a high index of suspicion must be maintained, as the diagnostic techniques require targeted investigations and specific collection and transportation of the samples. Empiric treatment recommendations are available, but owing to the increasing resistance of this pathogen, susceptibility testing is needed for every diagnosed case. We intend to raise awareness regarding these infections, as they tend to be more frequent than they were in the past and to appear in areas where they had not been recognized before.

Marine anoxia impede the transformation of dissolved organic carbon released by kelp into refractory dissolved organic carbon

The transformation of dissolved organic carbon (DOC) released by macroalgae into refractory dissolved organic carbon (RDOC) through microbial carbon pump (MCP) represents a crucial carbon sequestration process. This process mainly takes place in coastal areas, where it is likely affected by marine anoxia. The interactions between the components of DOC released by kelp and the community structure of heterotrophic bacteria both under normoxic and anoxic conditions were studied by three-dimensional fluorescence parallel factor analysis (PARAFAC), Fourier Transform-Ion Cyclotron Resonance-Mass Spectrometry (FT-ICR-MS) and 16S rRNA high-throughput sequencing. Following 240 days of decomposition, we found that the proportion of labile dissolved organic carbon (LDOC) was 4.61 % greater under anoxic conditions compared to normoxic conditions. Conversely, the proportion of RDOC was 8.06 % lower under anoxic conditions than under normoxic conditions. These findings suggest that anoxia hinders the conversion of LDOC to RDOC in the DOC released by kelp. Although normoxic conditions favor RDOC production, anoxic conditions could be more advantageous for the transport of DOC to the deep ocean, potentially enhancing carbon sequestration. The cultivation of macroalgae in anoxic zones may further boost their carbon sequestration potential.

Recent Discovery of Diverse Prophages Located in Genomes of Vibrio spp. and Their Implications for Bacterial Pathogenicity, Environmental Fitness, Genome Evolution, Food Safety, and Public Health

Bacteria in the genus Vibrio, including at least 152 species, thrive in marine and estuarine environments and are frequently detected in aquatic products worldwide. Of these, 12 species have been implicated in human infectious diseases, such as the life-threatening pandemic cholera, acute gastroenteritis, and severe sepsis. Nevertheless, molecular mechanisms of their pathogenesis are not fully uncovered yet. Prophages are found prevalent in Vibrio spp. genomes, carrying a number of genes with various functions. In this review, we deciphered the evolutionary relationship between prophages and Vibrio species and highlighted the impact of prophages on the bacterial pathogenicity, environmental fitness, and genome evolution, based on 149 newly discovered intact prophages located in the genomes of 82 Vibrio spp., which we searched and collected from Web of Science Core Collection in the most recent 5 years. The effects of prophages on resistance to superinfection, strain competition, and their regulation were also discussed. This review underscored crucial roles of prophages in shaping Vibrio spp. genomes and their implications for food safety and public health.

Advances in Vibrio-related infection management: an integrated technology approach for aquaculture and human health

Vibrio species pose significant threats worldwide, causing mortalities in aquaculture and infections in humans. Global warming and the emergence of worldwide strains of Vibrio diseases are increasing day by day. Control of Vibrio species requires effective monitoring, diagnosis, and treatment strategies at the global scale. Despite current efforts based on chemical, biological, and mechanical means, Vibrio control management faces limitations due to complicated implementation processes. This review explores the intricacies and challenges of Vibrio-related diseases, including accurate and cost-effective diagnosis and effective control. The global burden due to emerging Vibrio species further complicates management strategies. We propose an innovative integrated technology model that harnesses cutting-edge technologies to address these obstacles. The proposed model incorporates advanced tools, such as biosensing technologies, the Internet of Things (IoT), remote sensing devices, cloud computing, and machine learning. This model offers invaluable insights and supports better decision-making by integrating real-time ecological data and biological phenotype signatures. A major advantage of our approach lies in leveraging cloud-based analytics programs, efficiently extracting meaningful information from vast and complex datasets. Collaborating with data and clinical professionals ensures logical and customized solutions tailored to each unique situation. Aquaculture biotechnology that prioritizes sustainability may have a large impact on human health and the seafood industry. Our review underscores the importance of adopting this model, revolutionizing the prognosis and management of Vibrio-related infections, even under complex circumstances. Furthermore, this model has promising implications for aquaculture and public health, addressing the United Nations Sustainable Development Goals and their development agenda.

Non-cholera Vibrio infections in Southeast Asia: A systematic review and meta-analysis

We reviewed and analyzed the existing data on vibriosis in Southeast Asia to better understand its burden and prevalent causal agents. We searched PubMed, Web of Science, and EMBASE for studies published between January 2000 and April 2024. A random-effects meta-analysis was used to estimate the pooled isolation rate of non-cholera Vibrio species. Among the 1385 retrieved studies, 22 met the inclusion criteria for the systematic review and 11 were included in the meta-analysis. The pooled isolation rate of non-cholera Vibrio species among diarrheal patients was 5.0 %. Most species that caused vibriosis included V. parahaemolyticus, V. mimicus, V. vulnificus, non-O1/non-O139 V. cholerae, V. fluvialis, and V. alginolyticus. Pooled isolation rate of V. parahaemolyticus and non-O1 V. cholerae were 7.0, and 4.0, respectively. The prevalence of vibriosis in Southeast Asia is non-negligible. Public health strategies should prioritize enhanced surveillance, and clinicians should consider vibriosis in diarrheal patients with seafood consumption history.

Understanding the role of microbes in health and disease of farmed aquatic organisms

Aquaculture is critical to reduce protein deficiencies and supplement the world's demand for seafood. However, the culture environment predisposes farmed animals to infectious diseases. In particular, the high density of fish, crustacean, mollusk, sea cucumber or algal species allows for the rapid spread of infectious diseases resulting in devastating losses. Massive amounts of antibiotics have been used to sustain aquaculture production. This has led to the critical need to evaluate the impact of current control measures and optimize disease management schemes with an emphasis on global impact and sustainability. Furthermore, local and global changes have enhanced the pathogens' effects over aquaculture settings because increased temperature and pollution may trigger virulence genes and toxin production. Technological developments including biofloc technology, integrated multitrophic systems, recirculating aquaculture systems and probiotics have contributed to enhancing aquaculture sustainability and reducing the need for high loads of antibiotics and other chemicals. Furthermore, biotechnological tools (e.g., omics and cell biology) have shed light on cellular processes in the health and disease of reared organisms. Metagenomics is a reliable and relatively quick tool to identify microbial communities in aquaculture settings.

Pathological and oxidative stress responses of Mytilus galloprovincialis to Vibrio mediterranei infection: An in vivo challenge

Since the identification of Vibrio mediterranei as a causative agent in mass mortalities of pen shells across the Mediterranean, elucidating its pathogenicity, virulence, and interactions with other bivalves has gained importance. While the cellular and immune responses of bivalves to various Vibrio species have been extensively studied, the infectious characteristics of this Vibrio species, particularly in the context of pen shell outbreaks, remain unclear for other bivalves. Therefore, to evaluate its pathogenicity, we investigated the histological and oxidative effects on the Mediterranean mussel (Mytilus galloprovincialis), a key species in aquaculture. Two distinct infection setups were established: one involving the inoculation of seawater with the bacterial isolate and another involving direct injection of the bacteria into the mussels. After a 24-h exposure period, histological evaluations were conducted on the mantle, gill, and digestive gland tissues of the mussels. Additionally, measurements of superoxide dismutase (SOD), catalase (CAT), glutathione-S-transferase (GST), and lipid peroxidation levels were performed in the gill and digestive gland tissues. Oxidative responses were significantly elevated in both infection setups compared to the control group, with the directly injected samples exhibiting the highest oxidative responses (p < 0.05). Histological findings indicated that tissue-specific responses to host-pathogen interactions were consistent under both infection conditions. Notable observations included intense hemocytic infiltration in tissues, epithelial hyperplasia, and vacuolization in the gills, as well as focal necrotic areas in the digestive gland. The findings of this study indicate that V. mediterranei, a relatively novel pathogen, can provoke significant acute immune responses and tissue-level reactions in M. galloprovincialis, a species that is both widely distributed and vital to the food chain. These insights into the potential susceptibility of mussels underscore the need for further comprehensive research and inform the development of effective management strategies.

Enterovibrio qingdaonensis sp. nov. and Enterovibrio gelatinilyticus sp. nov., two marine bacteria isolated from surface seawater of Qingdao offshore

Two Gram-stain-negative, facultatively anaerobic, motile, and rod-shaped marine bacteria, designated strains ZSDZ35T and ZSDZ42T, were isolated from surface seawater of Qingdao offshore. Phylogenetic analysis of the 16S rRNA genes and whole genome data placed ZSDZ35T and ZSDZ42T within the genus Enterovibrio. Strain ZSDZ35T was most closely related to Enterovibrio nigricans DSM 22720T with 97.55% sequence similarity, whereas ZSDZ42T was most closely related to Enterovibrio calviensis DSM 14347T with 98.97% sequence similarity. Strain ZSDZ35T grew with 0-8% (w/v) NaCl (optimum 4%), at 16-37 °C (optimum 28 °C) and pH 6.0-9.0 (optimum pH 8.0); whereas strain ZSDZ42T grew with 1-7% (w/v) NaCl (5%), at 4-28 °C (8 °C) and pH 6.0-9.0 (pH 7.0). Both strains shared the same major fatty acid components of summed feature 3 (C16:1ω7c or/and C16:1ω6c), summed feature 8 (C18:1ω7c and C18:1ω6c) and C16:0, with different proportions. The DNA G + C contents of strains ZSDZ35T and ZSDZ42T were 47.2% and 46.7%, respectively. Based on the results of polyphasic analyses, ZSDZ35T and ZSDZ42T are considered to represent novel species, for which the names Enterovibrio qingdaonensis sp. nov. (type strain, ZSDZ35T = MCCC 1K06293T = KCTC 82887T) and Enterovibrio gelatinilyticus sp. nov. (type strain, ZSDZ42T = MCCC 1K06294T = KCTC 82886T) are proposed, respectively.

Evidence for immune priming specificity and cross-protection against sympatric and allopatric Vibrio splendidus strains in the oyster Magalana (Crassostrea) gigas

Infections with pathogenic Vibrio strains are associated with high summer mortalities of Pacific oysters Magalana (Crassostrea) gigas, affecting production worldwide. This raises the question of how M. gigas cultures can be protected against deadly Vibro infection. There is increasing experimental evidence of immune priming in invertebrates, where previous exposure to a low pathogen load boosts the immune response upon secondary exposure. Priming responses, however, appear to vary in their specificity across host and parasite taxa. To test priming specificity in the Vibrio - M. gigas system, we used two closely related Vibrio splendidus strains with differing degrees of virulence towards M. gigas. These V. splendidus strains were either isolated in the same location as the oysters (sympatric, opening up the potential for co-evolution) or in a different location (allopatric). We extracted cell-free haemolymph plasma from infected and control oysters to test the influence of humoral immune effectors on bacterial growth in vitro. While addition of haemolypmph plasma in general promoted growth of both strains, priming by an exposure to a sublethal dose of bacterial cells lead to inhibitory effects against a subsequent challenge with a potentially lethal dose in vitro. Inhibitory effects and immune priming was strongest when oysters had been primed with the sympatric Vibrio strain, but inhibitory effects were seen both when challenged with the sympatric as well as against allopatric V. splendidus, suggesting some degree of cross protection. The stronger immune priming against the sympatric strain suggests that priming could be more efficient against matching local strains potentially adding a component of local adaptation or co-evolution to immune priming in oysters. These in vitro results, however, were not reflected in the in vivo infection data, where we saw increased bacterial loads following an initial challenge. This discrepancy might suggests that that it is the humoral part of the oyster immune system that produces the priming effects seen in our in vitro experiments.

Bacterial Communities across Multiple Ecological Niches (Water, Sediment, Plastic, and Snail Gut) in Mangrove Habitats

Microbial composition across substrates in mangroves, particularly in the Middle East, remains unclear. This study characterized bacterial communities in sediment, water, Terebralia palustris snail guts, and plastic associated with Avicennia marina mangrove forests in two coastal lagoons in the Sea of Oman using 16S rDNA gene MiSeq sequencing. The genus Vibrio dominated all substrates except water. In the gut of snails, Vibrio is composed of 80-99% of all bacterial genera. The water samples showed a different pattern, with the genus Sunxiuqinia being dominant in both Sawadi (50.80%) and Qurum (49.29%) lagoons. There were significant differences in bacterial communities on different substrata, in particular plastic. Snail guts harbored the highest number of unique Operational Taxonomic Units (OTUs) in both lagoons, accounting for 30.97% OTUs in Sawadi and 28.91% OTUs in Qurum, compared to other substrates. Plastic in the polluted Sawadi lagoon with low salinity harbored distinct genera such as Vibrio, Aestuariibacter, Zunongwangia, and Jeotgalibacillus, which were absent in the Qurum lagoon with higher salinity and lower pollution. Sawadi lagoon exhibited higher species diversity in sediment and plastic substrates, while Qurum lagoon demonstrated lower species diversity. The principal component analysis (PCA) indicates that environmental factors such as salinity, pH, and nutrient levels significantly influence bacterial community composition across substrates. Variations in organic matter and potential anthropogenic influences, particularly from plastics, further shape bacterial communities. This study highlights the complex microbial communities in mangrove ecosystems, emphasizing the importance of considering multiple substrates in mangrove microbial ecology studies. The understanding of microbial dynamics and anthropogenic impacts is crucial for shaping effective conservation and management strategies in mangrove ecosystems, particularly in the face of environmental changes.

Low salinity stress increases the risk of Vibrio parahaemolyticus infection and gut microbiota dysbiosis in Pacific white shrimp

BACKGROUND

Extreme precipitation events often cause sudden drops in salinity, leading to disease outbreaks in shrimp aquaculture. Evidence suggests that environmental stress increases animal host susceptibility to pathogens. However, the mechanisms of how low salinity stress induces disease susceptibility remain poorly understood.

METHODS

We investigated the acute response of shrimp gut microbiota exposed to pathogens under low salinity stress. For comparison, shrimp were exposed to Vibrio infection under two salinity conditions: optimal salinity (Control group) and low salinity stress (Stress group). High throughput 16S rRNA sequencing and real-time PCR were employed to characterize the shrimp gut microbiota and quantify the severity level of Vibrio infection.

RESULTS

The results showed that low salinity stress increased Vibrio infection levels, reduced gut microbiota species richness, and perturbed microbial functions in the shrimp gut, leading to significant changes in lipopolysaccharide biosynthesis that promoted the growth of pathogens. Gut microbiota of the bacterial genera Candidatus Bacilliplasma, Cellvibrio, and Photobacterium were identified as biomarkers of the Stress group. The functions of the gut microbiota in the Stress group were primarily associated with cellular processes and the metabolism of lipid-related compounds.

CONCLUSIONS

Our findings reveal how environmental stress, particularly low salinity, increases shrimp susceptibility to Vibrio infection by affecting the gut microbiota. This highlights the importance of avoiding low salinity stress and promoting gut microbiota resilience to maintain the health of shrimp.

Safety evaluation and effects of dietary phlorotannins on the growth, health, and intestinal microbiota of Litopenaeus vannamei

Phlorotannins are phenolic compounds with diverse biological activities, yet their efficacy in aquatic animals currently remains unclear. This investigation scrutinized the influence of phlorotannins on the growth, immunity, antioxidant capacity, and intestinal microbiota in Litopenaeus vannamei, concurrently evaluating the potential adverse effects of phlorotannins on L. vannamei. A base diet without phlorotannins supplementation was used as a control, and 4 groups of diets with different concentrations (0, 0.5, 1.0, 2.0 g kg-1) of phlorotannins were formulated and fed to juvenile shrimp (0.25 ± 0.01 g) for 60 days followed by a 24-h challenge with Vibrio parahaemolyticus with triplicate in each group. Compared with the control, dietary 2.0 g kg-1 phlorotannins significantly improved the growth of the shrimp. The activities of enzymes related to cellular immunity, humoral immunity, and antioxidants, along with a notable upregulation in the expression of related genes, significantly increased. After V. parahaemolyticus challenge, the cumulative survival rates of the shrimp demonstrated a positive correlation with elevated concentrations of phlorotannins. In addition, the abundance of Bacteroidetes and functional genes associated with metabolism increased in phlorotannins supplementation groups. Phlorotannins did not elicit any detrimental effects on the biological macromolecules or histological integrity of the hepatopancreas or intestines. Simultaneously, it led to a significant reduction in malondialdehyde content. All results indicated that phlorotannins at concentrations of 2.0 g kg-1 can be used as safe feed additives to promote the growth, stimulate the immune response, improve the antioxidant capacity and intestinal health of L. vannamei, and an protect shrimp from damage caused by oxidative stress.

EFSA Panel on Biological Hazards (BIOHAZ), Koutsoumanis K, Allende A, Alvarez‐Ordóñez A, Bolton D, Bover‐Cid S, Chemaly M, De Cesare A, Herman L, Hilbert F, Lindqvist R, Nauta M, Nonno R, Peixe L, Ru G, Simmons M, Skandamis P, Baker‐Austin C, Hervio‐Heath D, Martinez‐Urtaza J, Caro ES, Strauch E, Thébault A, Guerra B, Messens W, Simon AC, Barcia‐Cruz R, Suffredini E. Public health aspects of Vibrio spp. related to the consumption of seafood in the EU

Vibrio parahaemolyticus, Vibrio vulnificus and non-O1/non-O139 Vibrio cholerae are the Vibrio spp. of highest relevance for public health in the EU through seafood consumption. Infection with V. parahaemolyticus is associated with the haemolysins thermostable direct haemolysin (TDH) and TDH-related haemolysin (TRH) and mainly leads to acute gastroenteritis. V. vulnificus infections can lead to sepsis and death in susceptible individuals. V. cholerae non-O1/non-O139 can cause mild gastroenteritis or lead to severe infections, including sepsis, in susceptible individuals. The pooled prevalence estimate in seafood is 19.6% (95% CI 13.7-27.4), 6.1% (95% CI 3.0-11.8) and 4.1% (95% CI 2.4-6.9) for V. parahaemolyticus, V. vulnificus and non-choleragenic V. cholerae, respectively. Approximately one out of five V. parahaemolyticus-positive samples contain pathogenic strains. A large spectrum of antimicrobial resistances, some of which are intrinsic, has been found in vibrios isolated from seafood or food-borne infections in Europe. Genes conferring resistance to medically important antimicrobials and associated with mobile genetic elements are increasingly detected in vibrios. Temperature and salinity are the most relevant drivers for Vibrio abundance in the aquatic environment. It is anticipated that the occurrence and levels of the relevant Vibrio spp. in seafood will increase in response to coastal warming and extreme weather events, especially in low-salinity/brackish waters. While some measures, like high-pressure processing, irradiation or depuration reduce the levels of Vibrio spp. in seafood, maintaining the cold chain is important to prevent their growth. Available risk assessments addressed V. parahaemolyticus in various types of seafood and V. vulnificus in raw oysters and octopus. A quantitative microbiological risk assessment relevant in an EU context would be V. parahaemolyticus in bivalve molluscs (oysters), evaluating the effect of mitigations, especially in a climate change scenario. Knowledge gaps related to Vibrio spp. in seafood and aquatic environments are identified and future research needs are prioritised.

Shewanella phaeophyticola sp. nov. and Vibrio algarum sp. nov., isolated from marine brown algae

Two Gram-stain-negative, rod-shaped bacteria, designated as strains KJ10-1T and KJ40-1T, were isolated from marine brown algae. Both strains were catalase-positive, oxidase-positive, and facultative aerobic. Strain KJ10-1T exhibited optimal growth at 25 °C, pH 7.0, and 3 % NaCl, whereas strain KJ40-1T showed optimal growth at 25 °C, pH 7.0, and 2 % NaCl. The respiratory quinones of strain KJ10-1T were ubiquinone-8, ubiquinone-7, menaquinone-7, and methylated menaquinone-7, while the respiratory quinone of strain KJ40-1T was only ubiquinone-8. As major fatty acids, strain KJ10-1T contained C16 : 0, C17 : 1 ω8c, iso-C15 : 0, and summed feature 3 (C16 : 1  ω7c and/or C16 : 1  ω6c) and strain KJ40-1T contained C16 : 0 and summed features 3 and 8 (C18 : 1  ω7c and/or C18 : 1  ω6c). The major polar lipids in strain KJ10-1T were phosphatidylethanolamine, phosphatidylglycerol, and an unidentified aminolipid, whereas those in strain KJ40-1T were phosphatidylethanolamine, phosphatidylglycerol, and diphosphatidylglycerol. The DNA G+C contents of strains KJ10-1T and KJ40-1T were 42.1 and 40.8 mol%, respectively. Based on 16S rRNA gene sequences, strains KJ10-1T and KJ40-1T exhibited the closest relatedness to Shewanella saliphila MMS16-UL250T (98.6 %) and Vibrio rumoiensis S-1T (95.4 %), respectively. Phylogenetic analyses, based on both 16S rRNA and 92 housekeeping genes, showed that the strains formed distinct phylogenic lineages within the genera Shewanella and Vibrio. Digital DNA-DNA hybridization and orthologous average nucleotide identity values between strain KJ10-1T and other Shewanella species, as well as between strain KJ40-1T and other Vibrio species, were below the thresholds commonly accepted for prokaryotic species delineation. Based on the phenotypic, chemotaxonomic, and phylogenetic data, strains KJ10-1T and KJ40-1T represent novel species of the genera Shewanella and Vibrio, respectively, for which the names Shewanella phaeophyticola sp. nov. and Vibrio algarum sp. nov. are proposed, respectively. The type strains of S. phaeophyticola and V. algarum are KJ10-1T (=KACC 22589T=JCM 35409T) and KJ40-1T (=KACC 22588T=JCM 35410T), respectively.

Cellular and transcriptomic response to pathogenic and non-pathogenic Vibrio parahaemolyticus strains causing acute hepatopancreatic necrosis disease (AHPND) in Litopenaeus vannamei

The shrimp industry has historically been affected by viral and bacterial diseases. One of the most recent emerging diseases is Acute Hepatopancreatic Necrosis Disease (AHPND), which causes severe mortality. Despite its significance to sanitation and economics, little is known about the molecular response of shrimp to this disease. Here, we present the cellular and transcriptomic responses of Litopenaeus vannamei exposed to two Vibrio parahaemolyticus strains for 98 h, wherein one is non-pathogenic (VpN) and the other causes AHPND (VpP). Exposure to the VpN strain resulted in minor alterations in hepatopancreas morphology, including reductions in the size of R and B cells and detachments of small epithelial cells from 72 h onwards. On the other hand, exposure to the VpP strain is characterized by acute detachment of epithelial cells from the hepatopancreatic tubules and infiltration of hemocytes in the inter-tubular spaces. At the end of exposure, RNA-Seq analysis revealed functional enrichment in biological processes, such as the toll3 receptor signaling pathway, apoptotic processes, and production of molecular mediators involved in the inflammatory response of shrimp exposed to VpN treatment. The biological processes identified in the VpP treatment include superoxide anion metabolism, innate immune response, antimicrobial humoral response, and toll3 receptor signaling pathway. Furthermore, KEGG enrichment analysis revealed metabolic pathways associated with survival, cell adhesion, and reactive oxygen species, among others, for shrimp exposed to VpP. Our study proves the differential immune responses to two strains of V. parahaemolyticus, one pathogenic and the other nonpathogenic, enlarges our knowledge on the evolution of AHPND in L. vannamei, and uncovers unique perspectives on establishing genomic resources that may function as a groundwork for detecting probable molecular markers linked to the immune system in shrimp.

Combining CRISPR/Cas9 and natural excision for the precise and complete removal of mobile genetic elements in bacteria

Horizontal gene transfer, facilitated by mobile genetic elements (MGEs), is an adaptive evolutionary process that contributes to the evolution of bacterial populations and infectious diseases. A variety of MGEs not only can integrate into the bacterial genome but also can survive or even replicate like plasmids in the cytoplasm, thus requiring precise and complete removal for studying their strategies in benefiting host cells. Existing methods for MGE removal, such as homologous recombination-based deletion and excisionase-based methods, have limitations in effectively eliminating certain MGEs. To overcome these limitations, we developed the Cas9-NE method, which combines the CRISPR/Cas9 system with the natural excision of MGEs. In this approach, a specialized single guide RNA (sgRNA) element is designed with a 20-nucleotide region that pairs with the MGE sequence. This sgRNA is expressed from a plasmid that also carries the Cas9 gene. By utilizing the Cas9-NE method, both the integrative and circular forms of MGEs can be precisely and completely eliminated through Cas9 cleavage, generating MGE-removed cells. We have successfully applied the Cas9-NE method to remove four representative MGEs, including plasmids, prophages, and genomic islands, from Vibrio strains. This new approach not only enables various investigations on MGEs but also has significant implications for the rapid generation of strains for commercial purposes.IMPORTANCEMobile genetic elements (MGEs) are of utmost importance for bacterial adaptation and pathogenicity, existing in various forms and multiple copies within bacterial cells. Integrated MGEs play dual roles in bacterial hosts, enhancing the fitness of the host by delivering cargo genes and potentially modifying the bacterial genome through the integration/excision process. This process can lead to alterations in promoters or coding sequences or even gene disruptions at integration sites, influencing the physiological functions of host bacteria. Here, we developed a new approach called Cas9-NE, allowing them to maintain the natural sequence changes associated with MGE excision. Cas9-NE allows the one-step removal of integrated and circular MGEs, addressing the challenge of eliminating various MGE forms efficiently. This approach simplifies MGE elimination in bacteria, expediting research on MGEs.

Identification of promoter activity in gene-less cassettes from Vibrionaceae superintegrons

Integrons are genetic platforms that acquire new genes encoded in integron cassettes (ICs), building arrays of adaptive functions. ICs generally encode promoterless genes, whose expression relies on the platform-associated Pc promoter, with the cassette array functioning as an operon-like structure regulated by the distance to the Pc. This is relevant in large sedentary chromosomal integrons (SCIs) carrying hundreds of ICs, like those in Vibrio species. We selected 29 gene-less cassettes in four Vibrio SCIs, and explored whether their function could be related to the transcription regulation of adjacent ICs. We show that most gene-less cassettes have promoter activity on the sense strand, enhancing the expression of downstream cassettes. Additionally, we identified the transcription start sites of gene-less ICs through 5'-RACE. Accordingly, we found that most of the superintegron in Vibrio cholerae is not silent. These promoter cassettes can trigger the expression of a silent dfrB9 cassette downstream, increasing trimethoprim resistance >512-fold in V. cholerae and Escherichia coli. Furthermore, one cassette with an antisense promoter can reduce trimethoprim resistance when cloned downstream. Our findings highlight the regulatory role of gene-less cassettes in the expression of adjacent cassettes, emphasizing their significance in SCIs and their clinical importance if captured by mobile integrons.

LKB1 regulates autophagy through AMPK/TOR signaling pathway to alleviate the damage caused by Vibrio alginolyticus infection

LKB1 (liver kinase B1) is a key upstream kinase of AMPK and plays an important role in various cellular activities. While the function and mechanism of LKB1 have been widely reported in the study of tumor, there are few reports on its role in bacterial infectious diseases, especially in shrimp. In the present study, molecular characterization revealed that LvLKB1 has an open reading frame (ORF) of 1266 bp encoding 421 amino acids with a molecular weight of about 48 KDa, including the kinase region, N-terminal regulatory domain and C-terminal regulatory domain. LvLKB1 in hepatopancreas and hemocytes was significantly upregulated after infection with Vibrio alginolyticus (V. alginolyticus). After silencing LvLKB1 gene in Litopenaeus vannamei (L. vannamei) and artificially infecting V. alginolyticus, the survival rate of L. vannamei was significantly decreased. Subsequently, it was found that the expression of inflammatory factors in hepatopancreas and hemocytes of shrimp was up-regulated, and the expression of lipid oxidation factors was decreased after silencing LKB1, leading to the phenomenon of lipid accumulation in hepatopancreas. In order to explore the mechanism, autophagy levels of shrimp were detected after silencing LKB1, which showed that autophagy levels in hepatopancreas and hemocytes were significantly reduced. Further studies conclusively showed that silencing LvLKB1 inhibited AMPK phosphorylation induced by V. alginolyticus infection, thereby activating TOR pathway and inhibiting autophagy in shrimp. These results indicate that LvLKB1 regulates autophagy through AMPK/TOR signaling pathway to alleviate the damage caused by V. alginolyticus infection.

The effects of primary and secondary bacterial exposure on the seahorse (Hippocampus erectus) immune response

Evolutionary adaptations in the Syngnathidae teleost family (seahorses, pipefish and seadragons) culminated in an array of spectacular morphologies, key immune gene losses, and the enigmatic male pregnancy. In seahorses, genome modifications associated with immunoglobulins, complement, and major histocompatibility complex (MHC II) pathway components raise questions concerning their immunological efficiency and the evolution of compensatory measures that may act in their place. In this investigation heat-killed bacteria (Vibrio aestuarianus and Tenacibaculum maritimum) were used in a two-phased experiment to assess the immune response dynamics of Hippocampus erectus. Gill transcriptomes from double and single-exposed individuals were analysed in order to determine the differentially expressed genes contributing to immune system responses towards immune priming. Double-exposed individuals exhibited a greater adaptive immune response when compared with single-exposed individuals, while single-exposed individuals, particularly with V. aestuarianus replicates, associated more with the innate branch of the immune system. T. maritimum double-exposed replicates exhibited the strongest immune reaction, likely due to their immunological naivety towards the bacterium, while there are also potential signs of innate trained immunity. MHC II upregulated expression was identified in selected V. aestuarianus-exposed seahorses, in the absence of other pathway constituents suggesting a possible alternative or non-classical MHC II immune function in seahorses. Gene Ontology (GO) enrichment analysis highlighted prominent angiogenesis activity following secondary exposure, which could be linked to an adaptive immune process in seahorses. This investigation highlights the prominent role of T-cell mediated adaptive immune responses in seahorses when exposed to sequential foreign bacteria exposures. If classical MHC II pathway function has been lost, innate trained immunity in syngnathids could be a potential compensatory mechanism.

Antagonistic activity of Phaeobacter piscinae against the emerging fish pathogen Vibrio crassostreae in aquaculture feed algae

Aquaculture provides a rich resource of high-quality protein; however, the production is challenged by emerging pathogens such as Vibrio crassostreae. While probiotic bacteria have been proposed as a sustainable solution to reduce pathogen load in aquaculture, their application requires a comprehensive assessment across the aquaculture food chain. The purpose of this study was to determine the antagonistic effect of the potential probiotic bacterium Phaeobacter piscinae against the emerging fish pathogen V. crassostreae in aquaculture feed algae that can be an entry point for pathogens in fish and shellfish aquaculture. P. piscinae strain S26 produces the antibacterial compound tropodithietic acid (TDA). In a plate-based assay, P. piscinae S26 was equally to more effective than the well-studied Phaeobacter inhibens DSM17395 in its inhibition of the fish pathogens Vibrio anguillarum 90-11-286 and V. crassostreae DMC-1. When co-cultured with the microalgae Tetraselmis suecica and Isochrysis galbana, P. piscinae S26 reduced the maximum cell density of V. crassostreae DMC-1 by 2 log and 3-4 log fold, respectively. A TDA-deficient mutant of P. piscinae S26 inhibited V. crassostreae DMC-1 to a lesser extent than the wild type, suggesting that the antagonistic effect involves TDA and other factors. TDA is the prime antagonistic agent of the inhibition of V. anguillarum 90-11-286. Comparative genomics of V. anguillarum 90-11-286 and V. crassostreae DMC-1 revealed that V. crassostreae DMC-1 carries a greater arsenal of antibiotic resistance genes potentially contributing to the reduced effect of TDA. In conclusion, P. piscinae S26 is a promising new candidate for inhibition of emerging pathogens such as V. crassostreae DMC-1 in algal feed systems and could contribute to a more sustainable aquaculture industry.IMPORTANCEThe globally important production of fish and shellfish in aquaculture is challenged by disease outbreaks caused by pathogens such as Vibrio crassostreae. These outbreaks not only lead to substantial economic loss and environmental damage, but treatment with antibiotics can also lead to antibiotic resistance affecting human health. Here, we evaluated the potential of probiotic bacteria, specifically the newly identified strain Phaeobacter piscinae S26, to counteract these threats in a sustainable manner. Through a systematic assessment of the antagonistic effect of P. piscinae S26 against V. crassostreae DMC-1, particularly within the context of algal feed systems, the study demonstrates the effectiveness of P. piscinae S26 as probiotic and thereby provides a strategic pathway for addressing disease outbreaks in aquaculture. This finding has the potential of significantly contributing to the long-term stability of the industry, highlighting the potential of probiotics as an efficient and environmentally conscious approach to safeguarding aquaculture productivity against the adverse impact of pathogens.

Complete genome sequence of Vibrio sp. strain AH4, a close relative of Vibrio metoecus isolated from Nile tilapia (Oreochromis niloticus)

Here, I report the complete genome sequence of Vibrio sp. strain AH4, which had been isolated from moribund farmed Nile tilapia (Oreochromis niloticus). Assessment of the genome sequence of this strain revealed the presence of two linear chromosomes 2,894,109 bp and 1,082,372 bp.

Characterization of gill bacterial microbiota in wild Arctic char (Salvelinus alpinus) across lakes, rivers, and bays in the Canadian Arctic ecosystems

Teleost gill mucus has a highly diverse microbiota, which plays an essential role in the host's fitness and is greatly influenced by the environment. Arctic char (Salvelinus alpinus), a salmonid well adapted to northern conditions, faces multiple stressors in the Arctic, including water chemistry modifications, that could negatively impact the gill microbiota dynamics related to the host's health. In the context of increasing environmental disturbances, we aimed to characterize the taxonomic distribution of transcriptionally active taxa within the bacterial gill microbiota of Arctic char in the Canadian Arctic in order to identify active bacterial composition that correlates with environmental factors. For this purpose, a total of 140 adult anadromous individuals were collected from rivers, lakes, and bays belonging to five Inuit communities located in four distinct hydrologic basins in the Canadian Arctic (Nunavut and Nunavik) during spring (May) and autumn (August). Various environmental factors were collected, including latitudes, water and air temperatures, oxygen concentration, pH, dissolved organic carbon (DOC), salinity, and chlorophyll-a concentration. The taxonomic distribution of transcriptionally active taxa within the gill microbiota was quantified by 16S rRNA gene transcripts sequencing. The results showed differential bacterial activity between the different geographical locations, explained by latitude, salinity, and, to a lesser extent, air temperature. Network analysis allowed the detection of a potential dysbiosis signature (i.e., bacterial imbalance) in fish gill microbiota from Duquet Lake in the Hudson Strait and the system Five Mile Inlet connected to the Hudson Bay, both showing the lowest alpha diversity and connectivity between taxa.IMPORTANCEThis paper aims to decipher the complex relationship between Arctic char (Salvelinus alpinus) and its symbiotic microbial consortium in gills. This salmonid is widespread in the Canadian Arctic and is the main protein and polyunsaturated fatty acids source for Inuit people. The influence of environmental parameters on gill microbiota in wild populations remains poorly understood. However, assessing the Arctic char's active gill bacterial community is essential to look for potential pathogens or dysbiosis that could threaten wild populations. Here, we concluded that Arctic char gill microbiota was mainly influenced by latitude and air temperature, the latter being correlated with water temperature. In addition, a dysbiosis signature detected in gill microbiota was potentially associated with poor fish health status recorded in these disturbed environments. With those results, we hypothesized that rapid climate change and increasing anthropic activities in the Arctic might profoundly disturb Arctic char gill microbiota, affecting their survival.

Genomic and Proteomic Analyses of Extracellular Products Reveal Major Virulence Factors Likely Accounting for Differences in Pathogenicity to Bivalves between Vibrio mediterranei Strains

Vibrio mediterranei, a bacterial pathogen of bivalves, has exhibited strain-dependent virulence. The mechanisms behind the variations in bivalve pathogenicity between V. mediterranei strains have remained unclear. However, a preliminary analysis of the extracellular product (ECP) proteomes has revealed differences in protein compositions between low- and high-virulence strains; in addition to 1265 shared proteins, 127 proteins have been identified to be specific to one low-virulence strain and 95 proteins to be specific to two high-virulence strains. We further studied the ECP proteins of the three V. mediterranei strains from functional perspectives using integrated genomics and proteomics approaches. The results showed that lipid metabolism, transporter activity and membrane transporter pathways were more enriched in the ECPs of the two high-virulence strains than in those of the low-virulence strain. Additionally, 73 of the 95 high-virulence strain-specific proteins were found to have coding genes in the genome but were not expressed in the low-virulence strain. Moreover, comparisons with known virulence factors in the Virulence Factor Database (VFDB) and the Pathogen-Host Interactions Database (PHI-base) allowed us to predict more than 10 virulence factors in the categories of antimicrobial activity/competitive advantage, the effector delivery system and immune modulation, and the high-virulence strain-specific ECP proteins consisted of a greater percentage of known virulence factors than the low-virulence strain. Particularly, two virulence factors, MtrC and KatG, were identified in the ECPs of the two high-virulence strains but not in those of the low-virulence strain. Most coding genes of the ECP proteins including known virulence factors were identified on chromosome 1 of V. mediterranei. Our findings indicate that variations in virulence factor composition in the bacterial ECPs may partially account for the differences in the bivalve pathogenicity between V. mediterranei strains.

A Comparative Study on Effects of Three Butyric Acid-Producing Additives on the Growth Performance, Non-specific Immunity, and Intestinal Microbiota of the Sea Cucumber Apostichopus japonicus

The providers of butyric acid, Clostridium butyricum (CB), sodium butyrate (SB), and tributyrin (TB), have been extensively studied as aquafeed additives in recent years. However, no comparative study has been reported on the probiotic effects of CB, SB, and TB as feed additives on sea cucumber (Apostichopus japonicus). A 63-day feeding trial was performed to assess the effects of dietary live cells of C. butyricum (CB group, the basal diet supplemented with 1% CB), sodium butyrate (SB group, the basal diet supplemented with 1% SB), and tributyrin (TB group, the basal diet supplemented with 1% TB) on the growth, non-specific immunity, and intestinal microbiota of A. japonicus with a basal diet group as the control. Results indicated that all three additives considerably increased A. japonicus growth, with dietary CB having the optimal growth-promoting effect. Of the seven non-specific enzyme parameters measured in coelomocytes of A. japonicus (i.e., the activities of phagocytosis, respiratory burst, superoxide dismutase, alkaline phosphatase, acid phosphatase, catalase, and lysozyme), dietary CB, SB, and TB considerably increased the activities of six, five, and six of them, respectively. The immune genes (Aj-p105, Aj-p50, Aj-rel, and Aj-lys) expression in the mid-intestine tissues of A. japonicus was significantly increased by all three additives. The CB group had the highest expression of all four genes. Additionally, the relative expression of Aj-p105, Aj-p50, and Aj-lys genes was significantly up-regulated in the three additive groups after stimulation with inactivated Vibrio splendidus. Dietary CB enhanced the intestinal microbial diversity and richness in A. japonicus while dietary TB decreased them. Meanwhile, dietary CB, SB, and TB significantly enhanced the abundance of Firmicutes, unclassified_f_Rhodobacteraceae, and Proteobacteria, respectively, while dietary CB and SB reduced the abundance of Vibrio. Dietary CB and SB improved the stability of microbial ecosystem in the intestine of A. japonicus. In contrast, dietary TB appeared to have a negative effect on the stability of intestinal microbial ecosystem. All three additives improved the intestinal microbial functions associated with energy production and immunity regulation pathways, which may contribute directly to growth promotion and non-specific immunity enhancement in A. japonicus. Collectively, in terms of enhancing growth and non-specific immunity, as well as improving intestinal microbiota, dietary live cells of C. butyricum exhibited the most effective effects in A. japonicus.

Recovering high-quality bacterial genomes from cross-contaminated cultures: a case study of marine Vibrio campbellii

BACKGROUND

Environmental monitoring of bacterial pathogens is critical for disease control in coastal marine ecosystems to maintain animal welfare and ecosystem function and to prevent significant economic losses. This requires accurate taxonomic identification of environmental bacterial pathogens, which often cannot be achieved by commonly used genetic markers (e.g., 16S rRNA gene), and an understanding of their pathogenic potential based on the information encoded in their genomes. The decreasing costs of whole genome sequencing (WGS), combined with newly developed bioinformatics tools, now make it possible to unravel the full potential of environmental pathogens, beyond traditional microbiological approaches. However, obtaining a high-quality bacterial genome, requires initial cultivation in an axenic culture, which is a bottleneck in environmental microbiology due to cross-contamination in the laboratory or isolation of non-axenic strains.

RESULTS

We applied WGS to determine the pathogenic potential of two Vibrio isolates from coastal seawater. During the analysis, we identified cross-contamination of one of the isolates and decided to use this dataset to evaluate the possibility of bioinformatic contaminant removal and recovery of bacterial genomes from a contaminated culture. Despite the contamination, using an appropriate bioinformatics workflow, we were able to obtain high quality and highly identical genomes (Average Nucleotide Identity value 99.98%) of one of the Vibrio isolates from both the axenic and the contaminated culture. Using the assembled genome, we were able to determine that this isolate belongs to a sub-lineage of Vibrio campbellii associated with several diseases in marine organisms. We also found that the genome of the isolate contains a novel Vibrio plasmid associated with bacterial defense mechanisms and horizontal gene transfer, which may offer a competitive advantage to this putative pathogen.

CONCLUSIONS

Our study shows that, using state-of-the-art bioinformatics tools and a sufficient sequencing effort, it is possible to obtain high quality genomes of the bacteria of interest and perform in-depth genomic analyses even in the case of a contaminated culture. With the new isolate and its complete genome, we are providing new insights into the genomic characteristics and functional potential of this sub-lineage of V. campbellii. The approach described here also highlights the possibility of recovering complete bacterial genomes in the case of non-axenic cultures or obligatory co-cultures.

Genetic Insights into Biofilm Formation by a Pathogenic Strain of Vibrio harveyi

The Vibrio genus includes bacteria widely distributed in aquatic habitats and the infections caused by these bacteria can affect a wide range of hosts. They are able to adhere to numerous surfaces, which can result in biofilm formation that helps maintain them in the environment. The involvement of the biofilm lifestyle in the virulence of Vibrio pathogens of aquatic organisms remains to be investigated. Vibrio harveyi ORM4 is a pathogen responsible for an outbreak in European abalone Haliotis tuberculata populations. In the present study, we used a dynamic biofilm culture technique coupled with laser scanning microscopy to characterize the biofilm formed by V. harveyi ORM4. We furthermore used RNA-seq analysis to examine the global changes in gene expression in biofilm cells compared to planktonic bacteria, and to identify biofilm- and virulence-related genes showing altered expression. A total of 1565 genes were differentially expressed, including genes associated with motility, polysaccharide synthesis, and quorum sensing. The up-regulation of 18 genes associated with the synthesis of the type III secretion system suggests that this virulence factor is induced in V. harveyi ORM4 biofilms, providing indirect evidence of a relationship between biofilm and virulence.

Effects of nanoplastics on the gut microbiota of Pacific white shrimp Litopenaeus vannamei

Nanoplastics (NPs) are an abundant, long-lasting, and widespread type of environmental pollution that is of increasing concern because of the serious threats they might pose to ecosystems and species. Identifying the ecological effects of plastic pollution requires understanding the effects of NPs on aquatic organisms. Here, we used the Pacific white shrimp (Litopenaeus vannamei) as a model species to investigate whether ingestion of polystyrene NPs affects gut microbes and leads to metabolic changes in L. vannamei. The abundance of Proteobacteria increased and that of Bacteroidota decreased after NPs treatment. Specifically, Vibrio spp., photobacterium spp., Xanthomarina spp., and Acinetobacter spp. increased in abundance, whereas Sulfitobacter spp. and Pseudoalteromonas spp. decreased. Histological observations showed that L. vannamei exposed to NP displayed a significantly lower intestinal fold height and damaged intestinal structures compared with the control group. Exposure to NPs also stimulated alkaline phosphatase, lysozyme, and acid phosphatase activity, resulting in an immune response in L. vannamei. In addition, the content of triglycerides, total cholesterol, and glucose were significantly altered after NP exposure. These results provided significant ecotoxicological data that can be used to better understand the biological fate and effects of NPs in L. vannamei.

One Health approach for prioritization of potential foodborne pathogens: Risk-ranking, Delphi survey, and criteria evaluation pre- and post-COVID-19 pandemic

Frequent foodborne illnesses with unknown causative agents highlight the need to explore zoonotic potential foodborne pathogens (PFPs). An effective PFP prioritization tool is indispensable, especially after experiencing the recent pandemic caused by zoonotic SARS-CoV-2. Risk information on pathogens (excluding 30 known foodborne pathogens) provided by governmental and international organizations was reviewed to generate a list of PFPs. Risk-ranking of PFPs was conducted based on a literature review of food poisoning or detection cases, and the ranks were determined with a decision tree. PFPs were prioritized by infectious disease (ID), veterinary medicine (VET), and food safety (FS) experts through a pre- and postpandemic Delphi survey, and key criteria in their decisions were illuminated. Among 339 PFPs, 32 rank-1 PFPs were involved in the foodborne outbreak(s). Discrepancies in opinions on prioritization between experts in different fields deepened after the pandemic. Only VET and FS experts valued the plausibility of foodborne transmission in evaluating bacteria and viruses, and a significant correlation between their selection of PFPs was found (p < .05). The impact of the pandemic induced all fields to focus more on human transmission and severity/fatality in prioritizing viruses, and only FS experts emphasized the plausibility of foodborne transmission after the pandemic. In contrast to prioritizing bacteria or viruses, ID and VET experts are unusually focused on foodborne transmission when prioritizing parasites. Criteria of consensus deduced by interdisciplinary experts with different interests and the criteria directly related to foodborne transmission should be acknowledged for adequate PFP prioritization.

Impact of THIONIL® on reducing water and soil micro-pollutant and enhancement of growth, survival, anti-vibrio, immunity and health indices of Litopenaeus vannamei in pond trial

There is an urgent requirement for the improvement of the white leg shrimp, Litopenaeus vannamei; health-related indices; and immunity due to emerging diseases. Recently, probiotics have been playing an important role in L. vannamei health management. Therefore, the current pond trial was to evaluate the probiotic proficiency of commercial probiotic products of THIONIL (THIO) on the enhancement of the water, soil, growth, digestibility, survival, immune-related indices, and susceptibility of L. vannamei to infection. The study was carried out in the major shrimp culturing regions of Kavali, Nellore (Andhra Pradesh), and Ponneri (Tamil Nadu), India. Six groups (lacks/ha) of the experimental L. vannamei were allocated, including a control group (THIO 0%-untreated) and groups containing 2%, 4%, 6%, 8%, and 10% of THIO that were encapsulated with commercial feed (CP Aqua). Bioassays were performed on PLs/ shrimp at various days interval of 0, 5, 25, 50, 100, and 123th to assess productivity, anti-vibrio activity, and digestive enzyme for digestibility, histological and immunological indices, and cytotoxicity in Artemia nauplii. Significant differences were observed in the increased growth (35.71 ± 3.24 g/shrimp) and digestive parameters in 10% THIO-fed shrimp. Although in contrast to the control group, the other THIO-fed prawn groups also displayed appreciable development. The findings showed that, in comparison to the control, the gill, hepatopancreas, and stomach had reduced tissue damage with 10% THIO. Furthermore, Vibrio parahaemolyticus (0.008 × 104 cfu/g) and Vibrio harveyi (0.051 × 105 cfu/g) (vibriosis) were potentially resistant to the 10% THIO-fed group. In addition, THIO-fed prawns (10%) showed significant improvements in immune-related expresses (proPO, SOD, and SOA) in comparison to the control. In conclusion, the findings showed that the THIO treatment prawns significantly improved the quality of their water (pH, ammonia, nitrogen dioxide, hydrogen sulfide, and DO) and soil (Pb, Cr, Hg, Mg, Cu, Fe, and Ni), increased and demonstrated protection against vibrio infections.

Oxidative stress, gene expression and histopathology of cultured gilthead sea bream (Sparus aurata) naturally co-infected with Ergasilus sieboldi and Vibrio alginolyticus

BACKGROUND

Parasitic and bacterial co-infections have been associated with increasing fish mortalities and severe economic losses in aquaculture through the past three decades. The aim of this study was to evaluate the oxidative stress, histopathology, and immune gene expression profile of gilthead sea bream (Sparus aurata) co-infected with Ergasilus sieboldi and Vibrio alginolyticus.

RESULTS

Vibrio alginolyticus and Ergasilus sieboldi were identified using 16 S rRNA and 28 S rRNA sequencing, respectively. The collagenase virulence gene was found in all Vibrio alginolyticus isolates, and the multiple antimicrobial resistance index ranged from 0.286 to 0.857. Oxidant-antioxidant parameters in the gills, skin, and muscles of naturally infected fish revealed increased lipid peroxidation levels and a decrease in catalase and glutathione antioxidant activities. Moreover, naturally co-infected gilthead sea bream exhibited substantial up-regulation of il-1β, tnf-α, and cyp1a1. Ergasilus sieboldi encircled gill lamellae with its second antennae, exhibited severe gill architectural deformation with extensive eosinophilic granular cell infiltration. Vibrio alginolyticus infection caused skin and muscle necrosis in gilthead sea bream.

CONCLUSION

This study described some details about the gill, skin and muscle tissue defense mechanisms of gilthead sea bream against Ergasilus sieboldi and Vibrio alginolyticus co-infections. The prevalence of co-infections was 100%, and no resistant fish were detected. These co-infections imbalance the health status of the fish by hampering the oxidant-antioxidant mechanisms and proinflammatory/inflammatory immune genes to a more detrimental side. Our results suggest that simultaneous screening for bacterial and parasitic pathogens should be considered.

Growth performance, gut microbiota composition, health and welfare of European sea bass (Dicentrarchus labrax) fed an environmentally and economically sustainable low marine protein diet in sea cages

The large use of fish meal/fish oil in carnivorous fish feeds is the main concern regarding environmental sustainability of aquaculture. Here, we evaluated the effects of an innovative diet, designed to be (1) environmentally sustainable by lowering the marine protein content while being (2) cost effective by using sustainable alternative raw materials with acceptable cost and produced on an industrial scale, on growth performance, gut microbiota composition, health and welfare of European sea bass (Dicentrarchus labrax), a key species of the Mediterranean marine aquaculture, reared in sea cages. Results show that the specific growth rate of fish fed the low marine protein diet was significantly lower than those fed conventional diet (0.67% vs 0.69%). Fatty acid profile of fillets from fish fed a low marine protein diet presented significant lower n-6 and higher n-3 content when compared to conventional ones. Then, a significant increase in the abundance of Vibrio and reduction of Photobacterium were found in the gut of fish fed with the low marine protein diet but effects on sea bass health needs further investigation. Finally, no major health and welfare alterations for fish fed the low marine protein diet were observed, combined with a potential slight benefit related to humoral immunity. Overall, these results suggest that despite the low marine protein diet moderately affects growth performance, it nevertheless may enhance environmental and economic sustainability of the sea bass aquaculture.

Diploid and triploid Chinook salmon (Oncorhynchus tshawytscha) have altered microRNA responses in immune tissues after infection with Vibrio anguillarum

Production of sterile fishes through artificial retention of a third set of chromosomes (triploidy) is a sustainable alternative for aquaculture since it reduces escapee pressure on wild populations. However, these fishes have reduced survival in stressful conditions and in response to infection. In this study, the impact of Vibrio anguillarum infection on diploid and triploid Chinook salmon (Oncorhynchus tshawytscha) was investigated to identify if there was any significant immune regulation by microRNAs (miRNA). Small RNAs from hindgut, head kidney, and spleen were sequenced to determine if miRNA transcript abundance was altered due to ploidy and infection in nine-month old full-sibling diploids and triploids. All three tissues had differentially expressed miRNA prior to infection, indicating subtle changes in epigenetic regulation due to increased ploidy. Additionally, miRNA were altered by infection, but there was only a difference in spleen miRNA expression between diploids and triploids at three days of infection. Furthermore, one miRNA (ssa-miR-2188-3p) was confirmed as having an altered response to infection in triploids compared to diploids, implicating potential immune dysregulation due to increased ploidy. The miRNAs identified in this study are predicted to target immune pathways, providing evidence for their importance in regulating responses to pathogens. This study is the first to investigate how increased ploidy alters miRNA expression in response to infection. Additionally, it provides evidence for epigenetic dysregulation in triploid fishes, which may contribute to their poor performance in response to stress.

Isolation, Identification, and Pathogenicity of Vibrio gigantis Retrieved from European Seabass (Dicentrarchus labrax) Farmed in Türkiye

In this study, V. gigantis strain C24 was isolated from cases of winter mortalities of hatchery-reared European seabass (Dicentrarchus labrax) broodstock in Türkiye. The first mortalities were reported in September 2016 and occurred annually in early autumn/late winter until the end of February 2019, when 15% of accumulated mortality was recorded. Diseased moribund fish exhibited general septicemic signs, including dermal ulcerations with hemorrhagic margins, distended abdomens, and hemorrhages below the pectorals, pelvic fins, and at the operculum. Postmortem findings showed congestion in several internal organs, hemorrhagic ascitic fluid, and congested prolapsed anal openings. The representative bacterial isolate V. gigantis strain C24 was characterized as Gram-negative, motile, nitrite-producing, and as vibrio static agent O/129-sensitive. The full-length 16S rRNA sequence (Accession No. ON778781) and gyrB gene sequence (Accession No. ON792326) of the C24 strain showed high similarity to V. gigantis strains. Moreover, the whole-genome average nucleotide identity (ANI) values (ANI > 97.7%) against four V. gigantis strains above the species demarcation limit unambiguously identified the C24 isolate as a member of this species. A preliminary virulence-gene analysis showed that the V. gigantis isolate C24 encoded at least three exotoxins, including two aerolysins and a thermolabile hemolysin. The experimental infection showed that the C24 isolate exhibited low to moderate virulence in experimentally infected European seabass juveniles. Interestingly, antimicrobial susceptibility testing revealed that the C24 isolate was susceptible to nalidixic acid, ciprofloxacin, and several other antibiotics but resistant to tilmicosin, kanamycin, streptomycin, and ampicillin. To our knowledge, this study is the first to report that V. gigantis could be considered an emerging bacterial pathogen in Türkiye, and it may threaten the international European seabass production.

PlzD modifies Vibrio vulnificus foraging behavior and virulence in response to elevated c-di-GMP

IMPORTANCE

Many free-swimming bacteria propel themselves through liquid using rotary flagella, and mounting evidence suggests that the inhibition of flagellar rotation initiates biofilm formation, a sessile lifestyle that is a nearly universal surface colonization paradigm in bacteria. In general, motility and biofilm formation are inversely regulated by the intracellular second messenger bis-(3´-5´)-cyclic dimeric guanosine monophosphate (c-di-GMP). Here, we identify a protein, PlzD, bearing a conserved c-di-GMP binding PilZ domain that localizes to the flagellar pole in a c-di-GMP-dependent manner and alters the foraging behavior, biofilm, and virulence characteristics of the opportunistic human pathogen, Vibrio vulnificus. Our data suggest that PlzD interacts with components of the flagellar stator to decrease bacterial swimming speed and changes in swimming direction, and these activities are enhanced when cellular c-di-GMP levels are elevated. These results reveal a physical link between a second messenger (c-di-GMP) and an effector (PlzD) that promotes transition from a motile to a sessile state in V. vulnificus.

Curcumin Alleviates Singapore Grouper Iridovirus-Induced Intestine Injury in Orange-Spotted Grouper (Epinephelus coioides)

Singapore grouper iridovirus (SGIV) is a new ranavirus species in the Iridoviridae family, whose high lethality and rapid spread have resulted in enormous economic losses for the aquaculture industry. Curcumin, a polyphenolic compound, has been proven to possess multiple biological activities, including antibacterial, antioxidant, and antiviral properties. This study was conducted to determine whether curcumin protected orange-spotted grouper (Epinephelus coioides) from SGIV-induced intestinal damage by affecting the inflammatory response, cell apoptosis, oxidative stress, and intestinal microbiota. Random distribution of healthy orange-spotted groupers (8.0 ± 1.0 cm and 9.0 ± 1.0 g) into six experimental groups (each group with 90 groupers): Control, DMSO, curcumin, SGIV, DMSO + SGIV, and curcumin + SGIV. The fish administered gavage received DMSO dilution solution or 640 mg/L curcumin every day for 15 days and then were injected intraperitoneally with SGIV 24 h after the last gavage. When more than half of the groupers in the SGIV group perished, samples from each group were collected for intestinal health evaluation. Our results showed that curcumin significantly alleviated intestine damage and repaired intestinal barrier dysfunction, which was identified by decreased intestine permeability and serum diamine oxidase (DAO) activity and increased expressions of tight junction proteins during SGIV infection. Moreover, curcumin treatment suppressed intestinal cells apoptosis and inflammatory response caused by SGIV and protected intestinal cells from oxidative injury by enhancing the activity of antioxidant enzymes, which was related to the activation of nuclear factor erythroid 2-related factor 2 (Nrf2) signaling. Moreover, we found that curcumin treatment restored the disruption of the intestinal microbiota caused by SGIV infection. Our study provided a theoretical basis for the functional development of curcumin in aquaculture by highlighting the protective effect of curcumin against SGIV-induced intestinal injury.

Assessment of Vibrio populations in a transect of Rhizophora mangle in Punta Galeta, Panamá: culture-dependent analyses reveal biotechnological applications

Introduction

Rhizophora mangle is considered an ecological niche for microorganisms with potentially novel and complex degrading enzymes.

Objective

To characterize Vibrio populations using culture-dependent methods, using samples collected from sediments and water along a red mangrove transect composed of three sites.

Methods

Strains were characterized according to their distribution, capacity to degrade of organic matter and other environmental parameters. Additionally the sequence diversity was assessed using 16S rRNA sequencing.

Results

Bacterial densities were strongly associated with temperature and salinity. A total of 87 good-quality sequences representing the isolates from the three sites, were binned into eight OTUs (Operational taxonomic units). Taxonomic assignment indicated that the dominant members were Vibrionaceae. Beta diversity analyses showed that bacterial communities clustered by sample source rather than spatial distribution, and that alpha diversity was found to be higher in water than in sediment. Three percent of the strains from water samples could degrade carboxyl-methyl cellulose with the smallest enzymatic indexes compared to 4 % of the strains from sediment samples that showed the highest enzymatic indexes. Two strains identified as Vibrio agarivorans degraded cellulose and agarose, producing the highest enzymatic indexes.

Conclusions

We found higher bacterial densities and diversity in the bacterial communities of the water samples compared to the sediment, with different OTUs including those similar to Ferrimonas, Providencia, or Shewanella which were not isolated in the sediment. Vibrio OTUs were shown to degrade cellulose in both sample types. The results of this study highlight the importance of red mangroves as Vibrio habitats and as reservoirs of potential enzyme sources with biotechnological applications.

Purification and Characterization of the Lecithin-Dependent Thermolabile Hemolysin Vhe1 from the Vibrio sp. Strain MA3 Associated with Mass Mortality of Pearl Oyster (Pinctada fucata)

In a previous study, we isolated a Vibrio sp. strain MA3 and its virulence factor, a hemolysin encoded by vhe1. This strain is associated with mass mortalities of the pearl oyster Pinctada fucata. In the present study, the vhe1 gene from strain MA3 was cloned and its encoded product was purified and characterized. Our results show that the vhe1 gene encodes a protein of 417 amino acids with an estimated molecular mass of 47.2 kDa and a pI of 5.14. The deduced protein, Vhe1, was found to contain the conserved amino acid sequence (GDSL motif) of the hydrolase/esterase superfamily and five conserved blocks characteristic of SGNH hydrolases. A BLAST homology search indicated that Vhe1 belongs the lecithin-dependent hemolysin/thermolabile hemolysin (LDH/TLH) family. In activity analyses, the optimal temperature for both the hemolytic and phospholipase activities of Vhe1 was 50 °C. Vhe1 hemolytic activity and phospholipase activity were highest at pH 8.5 and pH 8.0, respectively. However, both enzymatic activities sharply decreased at high temperature (> 50 °C) and pH < 7.0. Compared with previously reported hemolysins, Vhe1 appeared to be more thermal- and pH-labile. Both its hemolytic activity and phospholipase activity were significantly inhibited by CuCl2, CdCl2, ZnCl2, and NiCl2, and slightly inhibited by MnCl2 and CoCl2. Vhe1 showed higher phospholipase activity toward medium-chain fatty acids (C8-C12) than toward shorter- and longer-chain fatty acids. These results accumulate knowledge about the LDH/TLH of V. alginolyticus, which detailed characterization has not been reported, and contribute to solving of the mass mortality of pearl oyster.

Attenuation of a DNA cruciform by a conserved regulator directs T3SS1 mediated virulence in Vibrio parahaemolyticus

Pathogenic Vibrio species account for 3-5 million annual life-threatening human infections. Virulence is driven by bacterial hemolysin and toxin gene expression often positively regulated by the winged helix-turn-helix (wHTH) HlyU transcriptional regulator family and silenced by histone-like nucleoid structural protein (H-NS). In the case of Vibrio parahaemolyticus, HlyU is required for virulence gene expression associated with type 3 Secretion System-1 (T3SS1) although its mechanism of action is not understood. Here, we provide evidence for DNA cruciform attenuation mediated by HlyU binding to support concomitant virulence gene expression. Genetic and biochemical experiments revealed that upon HlyU mediated DNA cruciform attenuation, an intergenic cryptic promoter became accessible allowing for exsA mRNA expression and initiation of an ExsA autoactivation feedback loop at a separate ExsA-dependent promoter. Using a heterologous E. coli expression system, we reconstituted the dual promoter elements which revealed that HlyU binding and DNA cruciform attenuation were strictly required to initiate the ExsA autoactivation loop. The data indicate that HlyU acts to attenuate a transcriptional repressive DNA cruciform to support T3SS1 virulence gene expression and reveals a non-canonical extricating gene regulation mechanism in pathogenic Vibrio species.