Multilocus sequence analysis of the central clade of the genus Vibrio by using the 16S rRNA, recA, pyrH, rpoD, gyrB, rctB and toxR genes

Isolation optimization and screening of halophilic enzymes and antimicrobial activities of halophilic archaea from the high-altitude, hypersaline Da Qaidam Salt Lake, China

AIM

The aim of this study is to increase the diversity of culturable halophilic archaea by comparing various isolation conditions and to explore the application of halophilic archaea for enzyme-producing activities and antimicrobial properties.

METHODS AND RESULTS

We systematically compared the isolation performance of various archaeal and bacterial media by isolating halophilic archaea from the Da Qaidam Salt Lake, a magnesium sulfate subtype hypersaline lake on the Qinghai-Tibet Plateau, China, using multiple enrichment culture and gradient dilution conditions. A total of 490 strains of halophilic archaea were isolated, which belonged to five families and 11 genera within the order Halobacteriales of the class Halobacteria of the phylum Euryarchaeota. The 11 genera consisted of nine known genera and two potentially new genera, the former including Halorubrum, Natranaeroarchaeum, Haloplanus, Haloarcula, Halorhabdus, Halomicrobium, Halobacterium, Natrinema, and Haloterrigene. Halorubrum was the dominant genus with a relative abundance of 78.98%. By comparing different culture conditions, we found that bacterial media 2216E and R2A showed much better isolation performance than all archaeal media, and enrichment culture after 60 d and dilution gradients of 10-1 and 10-2 were best fitted for halophilic archaea cultivation. The screening of 40 halophilic archaeal strains of different species indicated that these halophilic archaea had great extracellular enzyme activities, including amylase (62.5%), esterase (50.0%), protease (27.5%), and cellulase (15.0%), and possessed great antimicrobial activities against human pathogens. A total of 34 strains exhibited antimicrobial activity against four or more pathogens, and 19 strains exhibited antimicrobial activity against all six pathogens.

CONCLUSIONS

The diversity of culturable halophilic archaea was significantly increased by enrichment culture and selection of bacterial media, and screening of representative strains showed that halophilic archaea have multiple extracellular enzyme activities and broad-spectrum antimicrobial activity against human pathogens.

Polyphasic identification of Vibrio species from aquatic sources using mass spectrometry, housekeeping gene sequencing and whole genome analysis

Accurate bacterial identification is essential for determining the causative agent of an infection, thus facilitating appropriate treatment and management strategies in both human and animal health contexts. Some species in the Vibrio genus are recognized pathogens, associated with a variety of infections. However, identification of these bacteria is oftentimes controversial. Therefore, we aimed to evaluate different identification approaches in terms of their reliability in distinguishing Vibrio species. To achieve this, we selected a set of 40 Vibrio isolates previously recovered from water and floating plastic samples in a large bay environment and identified them employing MALDI-TOF mass spectrometry, and rrs and pyrH gene sequencing. A subset of isolates was also submitted to whole genome sequencing. Overall, MALDI-TOF was found to be a fast-screening methodology for identification, notably at genus-level. However, for better species discrimination, pyrH gene sequencing stood out as a more reliable tool in contrast to rrs gene sequencing and MALDI-TOF, as corroborated by whole genome sequencing analysis.

Investigating dynamics, etiology, pathology, and therapeutic interventions of Caligus clemensi and Vibrio alginolyticus co-infection in farmed marine fish

This study investigated a disease outbreak characterized by caligid copepod infestations and subsequent secondary bacterial infections in European seabass (Dicentrarchus labrax) and flathead grey mullet (Mugil cephalus) cultivated at a private facility in the Deeba Triangle region of Egypt. Moribund fish displayed brown spots on the skin, tongue, and gills, along with lethargy and excess mucus. The fish suffered severe infections, exhibiting external hemorrhages, ulcers, and ascites. The fish had pale, enlarged livers with hemorrhaging. Comprehensive parasitological, bacteriological, molecular, immunity and histopathological analyses were conducted to identify the etiological agents and pathological changes. Caligid copepod infestation was observed in wet mounts from the buccal and branchial cavities of all examined fish, and the caligids were identified as Caligus clemensi through COI gene sequencing and phylogenetic analysis. Vibrio alginolyticus was confirmed as a secondary bacterial infection through biochemical tests, recA gene sequencing, and phylogenetic analyses. Antibiotic susceptibility testing revealed resistance to β-lactams, aminoglycosides, and trimethoprim-sulfamethoxazole in V. alginolyticus isolates. Upregulation of the inflammatory marker IL-1β in gill and skin tissues indicated a robust cell-mediated immune response against the pathogens. Histopathological examination revealed severe tissue damage, hyperplasia, hemorrhage, and congestion in the gills, along with hepatocellular degeneration and steatosis in the liver, providing initial insights into this outbreak. A comprehensive therapeutic regimen was implemented, comprising prolonged hydrogen peroxide immersion baths, followed by the application of the nature-identical plant-based compound Lice-less and probiotic Sanolife Pro-W supplementation. This integrated approach effectively eliminated C. clemensi infestations, controlled secondary bacterial infections, and restored fish health, reducing morbidity and mortality rates to minimal levels.

Multidrug-Resistance of Vibrio Species in Bivalve Mollusks from Southern Thailand: Isolation, Identification, Pathogenicity, and Their Sensitivity toward Chitooligosaccharide-Epigallocatechin-3-Gallate Conjugate

Vibrio spp. is a Gram-negative bacteria known for its ability to cause foodborne infection in association with eating raw or undercooked seafood. The majority of these foodborne illnesses are caused by mollusks, especially bivalves. Thus, the prevalence of Vibrio spp. in blood clams (Tegillarca granosa), baby clams (Paphia undulata), and Asian green mussels (Perna viridis) from South Thailand was determined. A total of 649 Vibrio spp. isolates were subjected to pathogenicity analysis on blood agar plates, among which 21 isolates from blood clams (15 isolates), baby clams (2 isolates), and green mussels (4 isolates) showed positive β-hemolysis. Based on the biofilm formation index (BFI) of β-hemolysis-positive Vibrio strains, nine isolates exhibited a strong biofilm formation capacity, with a BFI in the range of 1.37 to 10.13. Among the 21 isolates, 6 isolates (BL18, BL82, BL84, BL85, BL90, and BL92) were tlh-positive, while trh and tdh genes were not detected in all strains. Out of 21 strains, 5 strains showed multidrug resistance (MDR) against amoxicillin/clavulanic acid, ampicillin/sulbactam, cefotaxime, cefuroxime, meropenem, and trimethoprim/sulfamethoxazole. A phylogenetic analysis of MDR Vibrio was performed based on 16s rDNA sequences using the neighbor-joining method. The five MDR isolates were identified to be Vibrio neocaledonicus (one isolate), Vibrio fluvialis (one isolate) and, Vibrio cidicii (three isolates). In addition, the antimicrobial activity of chitooligosaccharide-epigallocatechin gallate (COS-EGCG) conjugate against MDR Vibrio strains was determined. The minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) of COS-EGCG conjugate were in the range of 64-128 µg/mL. The antimicrobial activity of the conjugate was advocated by the cell lysis of MDR Vibrio strains, as elucidated by scanning electron microscopic images. Vibrio spp. isolated from blood clams, baby clams, and Asian green mussels were highly pathogenic, exhibiting the ability to produce biofilm and being resistant to antibiotics. However, the COS-EGCG conjugate could be used as a potential antimicrobial agent for controlling Vibrio in mollusks.

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.

Vibrio intestinalis sp. nov., isolated from intestine of seahorse

A novel Gram-stain-negative, catalase- and oxidase-positive, facultatively anaerobic, and rod-shaped motile bacterial strain, designated as YLB-11^T, was isolated from seahorse intestine. The 16S rRNA gene sequencing analysis showed that YLB-11^T was most closely related Vibrio mytili LMG 19157^T (98.9 % nucleotide sequence identity). Phylogenetic analysis placed strain YLB-11^T within the genus Vibrio. The major cellular fatty acids were summed feature 3 (C_16: 1 ω6c/C_16 : 1 ω7c, 36.4 %), C_16 : 0 (19.1 %) and summed feature 8 (C_18:1 ω6c/C_18:1 ω7c, 12.3 %). The DNA G+C content of YLB-11^T was 44.7 mol %. The in silico DNA-DNA hybridization and average nucleotide identity values for whole-genome sequence comparisons between YLB-11^T and related species were clearly below the thresholds used for the delineation of a novel species. Therefore, YLB-11^T is considered to represent novel species of the genus Vibrio, for which the name Vibrio intestinalis sp. nov. is proposed. The type strain is YLB-11^T (=MCCC 1A17441^T=KCTC 72604^T).

Identification and Characterization of Infectious Pathogens Associated with Mass Mortalities of Pacific Oyster (Crassostrea gigas) Cultured in Northern China

The Pacific oyster (Crassostrea gigas) aquaculture industry increased rapidly in China with the introduction and promotion of triploid oysters in recent years. Mass mortalities affecting different life stages of Pacific oysters emerged periodically in several important production areas of Northern China. During 2020 and 2021, we conducted a passive two-year investigation of infectious pathogens linked to mass mortality. Ostreid herpesvirus-1 (OsHV-1) was detected to be associated with mass mortalities of hatchery larvae, but not juveniles and adults in the open sea. Protozoan parasites, such as Marteilia spp., Perkinsus spp. and Bonamia spp. were not detected. Bacterial isolation and identification revealed that Vibrio natriegens and Vibrio alginolyticus were the most frequently (9 out of 13) identified two dominant bacteria associated with mass mortalities. Pseudoalteromonas spp. was identified as the dominant bacteria in three mortality events that occurred during the cold season. Further bacteriological analysis was conducted on two representative isolates of V. natriegens and V. alginolyticus, designated as CgA1-1 and CgA1-2. Multisequence analysis (MLSA) showed that CgA1-1 and CgA1-2 were closely related to each other and nested within the Harveyi clade. Bacteriological investigation revealed faster growth, and more remarkable haemolytic activity and siderophore production capacity at 25 °C than at 15 °C for both CgA1-1 and CgA1-2. The accumulative mortalities of experimental immersion infections were also higher at 25 °C (90% and 63.33%) than at 15 °C (43.33% and 33.33%) using both CgA1-1 and CgA1-2, respectively. Similar clinical and pathological features were identified in samples collected during both naturally and experimentally occurring mortalities, such as thin visceral mass, discolouration, and connective tissue and digestive tube lesions. The results presented here highlight the potential risk of OsHV-1 to hatchery production of larvae, and the pathogenic role of V. natriegens and V. alginolyticus during mass mortalities of all life stages of Pacific oysters in Northern China.

Pathogenic and Opportunistic Vibrio spp. Associated with Vibriosis Incidences in the Greek Aquaculture: The Role of Vibrio harveyi as the Principal Cause of Vibriosis

A monitoring program to follow vibriosis incidents in the Greek marine aquaculture was implemented over the past 13 years. 273 isolates, from various cases originating from eight regions and nine hosts, were collected and characterized. The main aquaculture species of the survey were the European seabass (Dicentrarchus labrax) and the gilthead seabream (Sparus aurata). Various species of Vibrionaceae were associated with vibriosis. Vibrio harveyi had the highest prevalence and was isolated throughout the year from all hosts. During the warm months, Vibrio harveyi prevailed with frequent co-isolations of Photobacterium damselae subsp. damselae and Vibrio alginolyticus, while during spring, other Vibrio species were more abundant, such as Vibrio lentus, Vibrio cyclitrophicus, and Vibrio gigantis. Phylogenetic analysis using the mreB gene and the metabolic fingerprint of the isolates showed great variability within the species of the collection. The severity of the disease and the frequency of outbreaks make vibriosis (that is, mainly attributed to V. harveyi) an important concern for the regional aquaculture sector.

Antibiotic resistance, virulence and genetic characteristics of Vibrio alginolyticus isolates from aquatic environment in costal mariculture areas in China

Vibrio alginolyticus has been the second most common Vibrio species in the world and mainly grows in the ocean or estuary environment, which can induce epidemics outbreaks under marine organisms, and causing serious economic losses in aquaculture industry. In this study, the genetic populations and evolutionary relationship analysis of V. alginolyticus isolated from different geographical locations in China with typical interannual differences were exhibited originally genetic diversity. Then the virulence genes prevalence, antibiotic resistance phenotype, and antimicrobial resistance genes risk diversity of V. alginolyticus were analyzed by phenotypic and molecular typing methods. And they were complex correlations among antibiotic phenotypes, resistance and virulence genes under different genotype of V. alginolyticus. The results provide a theoretical foundation for further understanding the genetic and metabolic diversity among V. alginolyticus in China, and lay a theoretical foundation for the transmission risk assessment and regional diagnosis of Vibrio in aquatic animals.

Kribbellichelins A and B, Two New Antibiotics from Kribbella sp. CA-293567 with Activity against Several Human Pathogens

Current needs in finding new antibiotics against emerging multidrug-resistant superbugs are pushing the scientific community into coming back to Nature for the discovery of novel active structures. Recently, a survey of halophilic actinomyectes from saline substrates of El Saladar del Margen, in the Cúllar-Baza depression (Granada, Spain), led us to the isolation and identification of 108 strains from the rhizosphere of the endemic plant Limonium majus. Evaluation of the potential of these strains to produce new anti-infective agents against superbug pathogens was performed through fermentation in 10 different culture media using an OSMAC approach and assessment of the antibacterial and antifungal properties of their acetone extracts. The study allowed the isolation of two novel antibiotic compounds, kribbellichelin A (1) and B (2), along with the known metabolites sandramycin (3), coproporphyrin III (4), and kribelloside C (5) from a bioassay-guided fractionation of scaled-up active extracts of the Kribbella sp. CA-293567 strain. The structures of the new molecules were elucidated by ESI-qTOF-MS/MS, 1D and 2D NMR, and Marfey’s analysis for the determination of the absolute configuration of their amino acid residues. Compounds 1–3 and 5 were assayed against a panel of relevant antibiotic-resistant pathogenic strains and evaluated for cytotoxicity versus the human hepatoma cell line HepG2 (ATCC HB-8065). Kribbellichelins A (1) and B (2) showed antimicrobial activity versus Candida albicans ATCC-64124, weak potency against Acinetobacter baumannii MB-5973 and Pseudomonas aeruginosa MB-5919, and an atypical dose-dependent concentration profile against Aspergillus fumigatus ATCC-46645. Sandramycin (3) confirmed previously reported excellent growth inhibition activity against MRSA MB-5393 but also presented clear antifungal activity against C. albicans ATCC-64124 and A. fumigatus ATCC-46645 associated with lower cytotoxicity observed in HepG2, whereas Kribelloside C (5) displayed high antifungal activity only against A. fumigatus ATCC-46645. Herein, we describe the processes followed for the isolation, structure elucidation, and potency evaluation of these two new active compounds against a panel of human pathogens as well as, for the first time, the characterization of the antifungal activities of sandramycin (3).

Prevalence, Antibiotics Resistance and Plasmid Profiling of Vibrio spp. Isolated from Cultured Shrimp in Peninsular Malaysia

Vibrio is the most common bacterium associated with diseases in crustaceans. Outbreaks of vibriosis pose a serious threat to shrimp production. Therefore, antibiotics are commonly used as preventative and therapeutic measures. Unfortunately, improper use of antibiotics leads to antibiotic resistance. Nevertheless, information on the occurrence of Vibrio spp. and antibiotic use in shrimp, particularly in Malaysia, is minimal. This study aimed to provide information on the occurrence of Vibrio spp., its status of antibiotic resistance and the plasmid profiles of Vibrio spp. isolated from cultured shrimp in Peninsular Malaysia. Shrimp were sampled from seven farms that were located in different geographical regions of Peninsular Malaysia. According to the observations, 85% of the shrimp were healthy, whereas 15% were unhealthy. Subsequently, 225 presumptive Vibrio isolates were subjected to biochemical tests and molecular detection using the pyrH gene. The isolates were also tested for antibiotic susceptibility against 16 antibiotics and were subjected to plasmid profiling. Eventually, 13 different Vibrio spp. were successfully isolated and characterized using the pyrH gene. They were the following: V. parahaemolyticus (55%), V. communis (9%), V. campbellii (8%), V. owensii (7%), V. rotiferianus (5%), Vibrio spp. (4%), V. alginolyticus (3%), V. brasiliensis (2%), V. natriegens (2%), V. xuii (1%), V. harveyi (1%), V. hepatarius (0.4%) and P. damselae (3%). Antibiotic susceptibility profiles revealed that all isolates were resistant to penicillin G (100%), but susceptible to norfloxacin (96%). Furthermore, 16% of the isolates revealed MAR of less than 0.2, while 84% were greater than 0.2. A total of 125 isolates harbored plasmids with molecular weights between 1.0 and above 10 kb, detected among the resistant isolates. The resistant isolates were mediated by both chromosomal and plasmid factors. These findings support the use of surveillance data on the emerging patterns of antimicrobial-resistance and plasmid profiles of Vibrio spp. in shrimp farms. The findings from this study can be used to develop a better disease management strategy for shrimp farming.

Integrative omics analysis highlights the immunomodulatory effects of the parasitic dinoflagellate hhematodinium on crustacean hemocytes

Parasitic dinoflagellates in genus Hematodinium have caused substantial economic losses to multiple commercially valuable marine crustaceans around the world. Recent efforts to better understand the life cycle and biology of the parasite have improved our understanding of the disease ecology. However, studies on the host-parasite interaction, especially how Hematodinium parasites evade the host immune response are lacking. To address this shortfall, we used the comprehensive omics approaches (miRNA transcriptomics, iTRAQ-based proteomics) to get insights into the host-parasite interaction between hemocytes from Portunus trituberculatus and Hematodinium perezi in the present study. The parasitic dinoflagellate H. perezi remodeled the miRNome and proteome of hemocytes from challenged hosts, modulated the host immune response at both post-transcriptional and translational levels and caused post-transcriptional regulation to the host immune response. Multiple important cellular and humoral immune-related pathways (ex. Apoptosis, Endocytosis, ECM-receptor interaction, proPO activation pathway, Toll-like signaling pathway, Jak-STAT signaling pathway) were significantly affected by Hematodinium parasites. Through modulation of the host miRNome, the host immune responses of nodulation, proPO activation and antimicrobial peptides were significantly suppressed. Cellular homeostasis was imbalanced via post-transcriptional dysregulation of the phagosome and peroxisome pathways. Cellular structure and communication was seriously impacted by post-transcriptional downregulation of ECM-receptor interaction and focal adhesion pathways. In conclusion, H. perezi parasites could trigger striking changes in the miRNome and proteome of crustacean hemocytes, and this parasite exhibited multifaceted immunomodulatory effects and potential immune-suppressive mechanisms in crustacean hosts.

An Integrated Monitoring Approach to the Evaluation of the Environmental Impact of an Inshore Mariculture Plant (Mar Grande of Taranto, Ionian Sea)

The results of an ex-ante survey aiming to assess the impact of a fish farm in the Mar Grande of Taranto (southern Italy, Mediterranean Sea) on the surrounding environment are reported. There, the implementation of an innovative IMTA plant was planned, with the goals of environment bioremediation and commercially exploitable biomass production. Analyses were conducted in February and July 2018. Both seawater and sediments were sampled at the four corners of the fish farm to detect the existing biological and physico-chemical features. The investigation was performed to identify the best area of the farming plant for positioning the bioremediating system, but also to obtain a data baseline, to compare to the environmental status after the bioremediating action. Data were also analyzed by canonical analysis of principal coordinates (CAP). All the measurements, in particular, microbiology and macrobenthic community characterization using AZTI's Marine Biotic Index (AMBI) and the Multivariate-AMBI (M-AMBI) indices, suggest that the effect of fish farm waste was concentrated and limited to a small portion of the investigated area in relation to the direction of the main current. A site named A3, which was found to be the most impacted by the aquaculture activities, especially during the summer season, was chosen to place the bioremediation system.

An Integrative, Multiparametric Approach for the Comprehensive Assessment of Microbial Quality and Pollution in Aquaculture Systems

As the aquaculture sector significantly expanded worldwide in the past decades, the concept of sustainable aquaculture has developed with the challenge of not only maximizing benefits but also minimizing the negative impacts on the environment assuring, at the same time, food security. In this framework, monitoring and improving the microbiological water quality and animal health are a central topic. In the present study, we evaluated the seawater microbiological quality in a mariculture system located in a Mediterranean coastal area (Northern Ionian Sea, Italy). We furnished, for the first time, a microbial inventory based on conventional culture-based methods, integrated with the 16S rRNA gene metabarcoding approach for vibrios identification and diversity analyses, and further implemented with microbial metabolic profiling data obtained from the Biolog EcoPlate system. Microbiological pollution indicators, vibrios diversity, and microbial metabolism were determined in two different times of the year (July and December). All microbial parameters measured in July were markedly increased compared to those measured in December. The presence of potentially pathogenic vibrios is discussed concerning the risk of fish disease and human infections. Thus, the microbial inventory here proposed might represent a new multiparametric approach for the suitable surveillance of the microbial quality in a mariculture system. Consequently, it could be useful for ensuring the safety of both the reared species and the consumers in the light of sustainable, eco-friendly aquaculture management.

Isolation and Characterization of Vibrio kanaloae as a Major Pathogen Associated with Mass Mortalities of Ark Clam, Scapharca broughtonii, in Cold Season

High temperature is a risk factor for vibriosis outbreaks. Most vibrios are opportunistic pathogens that cause the mortality of aquatic animals at the vibrio optimal growth temperature (~25 °C), whereas a dominant Vibrio kanaloae strain SbA1-1 is isolated from natural diseased ark clams (Scapharca broughtonii) during cold seasons in this study. Consistent symptoms and histopathological features reappeared under an immersion infection with SbA1-1 performed at 15 °C. The pathogenicity difference of SbA1-1 was assessed under different temperatures (15 °C and 25 °C). The cumulative mortality rates of ark clams were significantly higher at the low temperature (15 °C) than at the high temperature (25 °C); up to 98% on 16th day post SbA1-1 infection. While the growth ratio of SbA1-1 was retarded at the low temperature, the hemolytic activity and siderophores productivity of SbA1-1 were increased. This study constitutes the first isolation of V. kanaloae from the natural diseased ark clams (S. broughtonii) in cold seasons and the exposition of the dissimilar pathogenicity of SbA1-1 at a different temperature. All the above indicates that V. kanaloae constitutes a threat to ark clam culture, especially in cold seasons.

Characterization of a novel shrimp pathogen, Vibrio brasiliensis, isolated from Pacific white shrimp, Penaeus vannamei

A novel pathogenic strain Vibrio 20190611023 was isolated from the hepatopancreas of moribund cultured Penaeus vannamei suffering from black gill disease. This strain was identified as V. brasiliensis based on the phylogenetic analyses of 16S rDNA gene and five other housekeeping genes (i.e., gapA, ftsZ, mreB, topA and gyrB). Some biochemical features of this strain were determined with an API 20NE system, and its haemolytic activity was determined using a sheep blood agar plate. The pathogenicity of this isolate 20190611023 was confirmed by the experimental challenge tests and histopathological examinations. P. vannamei were challenged via reverse gavage with different doses of bacterial suspensions. The calculated median lethal dose (LD₅₀ ) was (3.16 ± 1.78) × 10⁵  CFU/g (body weight). Moreover, antibiotic susceptibility tests were performed, the results of which showed that the strain 20190611023 was sensitive to chloramphenicol, compound sulphamethoxazole, ciprofloxacin, doxycycline and oxacillin, but resistant to erythromycin, kanamycin, gentamicin, cefoperazone, ceftriaxone, cefamezin and piperacillin. To our knowledge, this is the first report for demonstrating V. brasiliensis as a shrimp pathogen, which expands the host range of V. brasiliensis infection. The present study highlights that more attention should be paid to this novel pathogen in intensive shrimp aquaculture.

Disentangling the abundance and structure of Vibrio communities in a semi-enclosed Bay with mariculture (Dongshan Bay, Southern China)

The genus Vibrio contains a diverse group of heterotrophic bacteria, which are members of ubiquitous and abundant microbial communities in coastal ecosystems. Vibrio has been frequently found in a wide range of marine environments either by employing Vibrio-specific 16S rRNA sequencing or culturing methods. A combination of molecular and cultivation-dependent methods was developed to more precisely discriminate between different members of the genus Vibrio in seawater. This newly developed assay was subsequently applied to characterize Vibrio community composition in surface water at 18 mariculture sites. It Substantially improved the taxonomic resolution of Vibrio species when compared to traditional 16S rRNA analysis. Our qPCR and cultivation analyses revealed that average Vibrio abundance (Vibrio 16S rRNA gene copy numbers: 3.46 × 10⁶ to 6.70 × 10⁶ copies L⁻¹) and live cell numbers (5.65 × 10⁴–5.75 × 10⁵ cfu mL⁻¹) are significantly related to pH. Total bacteria and Vibrio-specific 16S rRNA metabarcode sequenceing resulted in a total of 10 and 32 operational taxonomic units (OTUs), respectively, and 15 Vibrio species were identified by targeted cultivation of Vibrio strains, with Vibrio fortis and V. brasiliensis dominating in the mariculture areas. The purpose of this study was to combine several analytical methods to improve current sequence-based Vibrio community surveys, and to prove for the effectiveness of this methodological approach comprehensively testing for Vibrio dynamics in different coastal environments.

Delineating virulence of Vibrio campbellii: a predominant luminescent bacterial pathogen in Indian shrimp hatcheries

Luminescent vibriosis is a major bacterial disease in shrimp hatcheries and causes up to 100% mortality in larval stages of penaeid shrimps. We investigated the virulence factors and genetic identity of 29 luminescent Vibrio isolates from Indian shrimp hatcheries and farms, which were earlier presumed as Vibrio harveyi. Haemolysin gene-based species-specific multiplex PCR and phylogenetic analysis of rpoD and toxR identified all the isolates as V. campbellii. The gene-specific PCR revealed the presence of virulence markers involved in quorum sensing (luxM, luxS, cqsA), motility (flaA, lafA), toxin (hly, chiA, serine protease, metalloprotease), and virulence regulators (toxR, luxR) in all the isolates. The deduced amino acid sequence analysis of virulence regulator ToxR suggested four variants, namely A123Q150 (AQ; 18.9%), P123Q150 (PQ; 54.1%), A123P150 (AP; 21.6%), and P123P150 (PP; 5.4% isolates) based on amino acid at 123rd (proline or alanine) and 150th (glutamine or proline) positions. A significantly higher level of the quorum-sensing signal, autoinducer-2 (AI-2, p = 2.2e-12), and significantly reduced protease activity (p = 1.6e-07) were recorded in AP variant, whereas an inverse trend was noticed in the Q150 variants AQ and PQ. The pathogenicity study in Penaeus (Litopenaeus) vannamei juveniles revealed that all the isolates of AQ were highly pathogenic with Cox proportional hazard ratio 15.1 to 32.4 compared to P150 variants; PP (5.4 to 6.3) or AP (7.3 to 14). The correlation matrix suggested that protease, a metalloprotease, was positively correlated with pathogenicity (p > 0.05) and negatively correlated (p < 0.05) with AI-2 and AI-1. The syntenic organization of toxS-toxR-htpG operon in V. campbellii was found to be similar to pathogenic V. cholerae suggesting a similar regulatory role. The present study emphasizes that V. campbellii is a predominant pathogen in Indian shrimp hatcheries, and ToxR plays a significant role as a virulence regulator in the quorum sensing-protease pathway. Further, the study suggests that the presence of glutamine at 150th position (Q150) in ToxR is crucial for the pathogenicity of V. campbellii.

Root Endophytes and Ginkgo biloba Are Likely to Share and Compensate Secondary Metabolic Processes, and Potentially Exchange Genetic Information by LTR-RTs

Ginkgo biloba is a pharmaceutical resource for terpenes and flavonoids. However, few insights discussed endophytes' role in Ginkgo, and whether genetic exchange happens between Ginkgo and endophytes remains unclear. Herein, functional gene profiles and repetitive sequences were analyzed to focus on these issues. A total of 25 endophyte strains were isolated from the Ginkgo root and distributed in 16 genera of 6 phyla. Significant morphological diversities lead to the diversity in the COG functional classification. KEGG mapping revealed that endophytic bacteria and fungi potentially synthesize chalcone, while endophytic fungi might also promote flavonoid derivatization. Both bacteria and fungi may facilitate the lignin synthesis. Aspergillus sp. Gbtc_1 exhibited the feasibility of regulating alcohols to lignans. Although Ginkgo and the endophytes have not observed the critical levopimaradiene synthase in ginkgolides synthesis, the upstream pathways of terpenoid precursors are likely intact. The MVK genes in Ginkgo may have alternative non-homologous copies or be compensated by endophytes in long-term symbiosis. Cellulomonas sp. Gbtc_1 became the only bacteria to harbor both MEP and MVA pathways. Endophytes may perform the mutual transformation of IPP and DMAPP in the root. Ginkgo and bacteria may lead to the synthesis and derivatization of the carotenoid pathway. The isoquinoline alkaloid biosynthesis seemed lost in the Ginkgo root community, but L-dopa is more probably converted into dopamine as an essential signal-transduction substance. So, endophytes may participate in the secondary metabolism of the Ginkgo in a shared or complementary manner. Moreover, a few endophytic sequences predicted as Ty3/Gypsy and Ty1/Copia superfamilies exhibited extremely high similarity to those of Ginkgo. CDSs in such endophytic LTR-RT sequences were also highly homologous to one Ginkgo CDS. Therefore, LTR-RTs may be a rare unit flowing between the Ginkgo host and endophytes to exchange genetic information. Collectively, this research effectively expanded the insight on the symbiotic relationship between the Ginkgo host and the endophytes in the root.

Isolation and characterization of marine bioluminescent bacteria for toxicity bioassays and biotechnological applications

Toxic heavy metals pollution posed severe health hazards to the environment and biodiversity. Therefore, the development of rapid and non-invasive bioassays is in the race to monitor toxic chemicals using novel approaches. This study isolated and characterized an intense blue luminescence-producing marine bacteria, Vibrio campbellii STF1, for biosensing applications. Species-level identification of this strain was confirmed based on various phenotypic tests and multilocus sequence approach using 16s rRNA, toxR, and luxA gene sequence analysis. Fatty acid methyl ester analysis revealed the presence of three predominant fatty acids C_{15:0 anteiso} (21.73%), C_{17:0 anteiso} (11.27%), and C_{19:0 anteiso} (9.08%) in STF1. Luciferase enzyme from V. campbellii STF1 was extracted, partially purified, and molecular masses (alpha subunit 40 kDa and beta subunit 37 kDa) were determined by SDS-PAGE gel for in vivo assays. MALDI-TOF-MS analysis of V. campbellii cells' protein extracts showed distinct mass spectral peaks at m/z of 2615, 3948, and 4232 da. V. campbellii STF1 is resistant to heavy metal lead, while other metals such as cadmium, copper, and mercury inhibited its growth and luminescence. Crude ethyl acetate extraction of V. campbellii demonstrated antibacterial activity against Shigella dysenteriae type 5 with a maximum inhibition zone of 27.0±1.0 mm.

Virulence properties and pathogenicity of multidrug-resistant Vibrio harveyi associated with luminescent vibriosis in pacific white shrimp, Penaeus vannamei

Global high demand for pacific white shrimp Penaeus vannamei has led to intensified cultivation and a wide range of disease problems, including bacterial diseases due to vibrios. Three presumptive luminescent Vibrio harveyi strains (Vh5, Vh8 and Vh10) were isolated from the hepatopancreas (Vh5) and haemolymph (Vh8 and Vh10) of diseased growout pacific white shrimp from a farm in Setiu, Terengganu, Malaysia, using Vibrio harveyi agar (VHA) differential medium. All three strains were identified as V. harveyi by biochemical characteristics. 16S rRNA gene-based phylogenetic analyses by neighbour-joining, maximum likelihood and maximum parsimony methods showed all three strains in the V. harveyi cluster. All three strains were β-haemolytic and positive for motility, biofilm formation and extracellular products (caseinase, gelatinase, lipase, DNase, amylase and chitinase). Vh10 was subjected to pathogenicity test in pacific white shrimp by immersion challenge and determined to have a LC₅₀ of 6.0 × 10⁸ CFU mL^-1 after 168 h of exposure. Antibiotic susceptibility tests showed that all strains were resistant to oxytetracycline (OXT30), oleandomycin (OL15), amoxicillin (AML25), ampicillin (AMP10) and colistin sulphate (CT25) but sensitive to doxycycline (DO30), flumequine (UB30), oxolinic acid (OA2), chloramphenicol (C30), florfenicol (FFC30), nitrofurantoin (F5) and fosfomycin (FOS50). Each strain was also resistant to a slightly different combination of eight other antibiotics, with an overall multiple antibiotic resistance (MAR) index of 0.40, suggesting prior history of heavy exposure to the antibiotics. Vh10 infection resulted in pale or discoloured hepatopancreas, empty guts, reddening, necrosis and luminescence of uropods, as well as melanized lesions in tail muscle. Histopathological examination showed necrosis of intertubular connective tissue and tubule, sloughing of epithelial cells in hepatopancreatic tubule, haemocytic infiltration, massive vacuolation and loss of hepatopancreatic tubule structure.

Comparative evaluation of Vibrio delineation methodologies in post-genomic era

Vibrios are widespread in both marine and coastal water environments and are recognized as one of the most important prokaryotic pathogens because they may potentially threaten the health of both aquacultures and human beings. However, owing to highly similar physiological and biochemical properties, accurate classification and identification of Vibrio strains remains challenging. This hampers further research on the physiology, pathogeny, genomics, epidemics, and ecology of vibrios. Here, we comparatively evaluated multiple approaches including 16S rRNA gene identity, average nucleotide identity (ANI), gene content similarity and mutilocus sequence analysis (MLSA) to investigate their ability in delineating Vibrio strains. In addition, we also evaluated the possibility of applying bacterial prophages in classifying and identifying Vibrio strains. Our results showed that MLSA outperformed other methods in discriminating Vibrio species, suggesting that the other four approaches should be used with cautions in Vibrio delineation. Interestingly, we also found that prophages identified in Vibrio strains were highly specific at strain- and species-level, suggesting that prophages held the potential to be used for microbial species, sub-species, and strain-level identifications. This study is expected to provide valuable insights into the taxonomic identification and classification of complex microbial groups in the post-genomic era.

Phylogenetic Revision of the Genus Aliivibrio: Intra- and Inter-Species Variance Among Clusters Suggest a Wider Diversity of Species

Genus Aliivibrio is known to harbor species exhibiting bioluminescence as well as pathogenic behavior affecting the fish farming industry. Current phylogenetic understanding of Aliivibrio has largely remained dormant after reclassification disentangled it from the Vibrio genus in 2007. There is growing evidence of wider diversity, but until now the lack of genomes and selective use of type strains have limited the ability to compare and classify strains firmly. In this study, a total of 143 bacterial strains, including 51 novel sequenced strains, were used to strengthen phylogenetic relationships in Aliivibrio by exploring intra-species and inter-species relations. Multilocus sequence analysis (MLSA), applying the six housekeeping genes 16S ribosomal RNA (rRNA), gapA, gyrB, pyrH, recA, and rpoA, inferred 12 clades and a singular branch in Aliivibrio. Along with four new phylogenetic clades, the MLSA resolved prior inconsistencies circumscribing Aliivibrio wodanis and formed a unique clade we propose as the novel species Aliivibrio sp. “friggae.” Furthermore, phylogenetic assessment of individual marker genes showed gyrB, pyrH, and recA superior to the 16S rRNA gene, resolving accurately for most species clades in Aliivibrio. In this study, we provide a robust phylogenetic groundwork for Aliivibrio as a reference point to classification of species.

Vibrio and major commercially important vibriosis diseases in decapod crustaceans

Bacteria fromthe Vibriogenus are autochthonous to aquatic environments and ubiquitous in aquaculture production systems. Many Vibrio species are non-pathogenic and can be commonly found in healthy farmed aquatic animals. However, some Vibrio species and strains are pathogenic leading to a variety of 'vibriosis' diseases. These diseases can have a significant negative impact on animal production, including farmed crustaceans such as shrimps, lobsters, and crabs. As such, vibriosis can pose a threat to meeting growing food demand and global food security. Preventive management is essential to avoid the onset of vibriosis. This includes a robust health management plan, the use of prophylaxis and treatment measures, and enhancing animal health through nutrition. Furthermore, the use of probiotics, prebiotics, synbiotics, quorum sensing disruption, green water, biofloc, bacteriophages, and immune priming could also play a role in preventing and controlling a vibriosis outbreak. This review aims to inform and update the reader about the current state of knowledge about Vibrio and associated vibriosis in farmed crustaceans (i.e. shrimp, lobster, and crabs). Furthermore, the review will identify potential knowledge gaps in the literature, which serves as a basis for future research priorities.

Pseudomonas pratensis sp. nov., Isolated from Grassland Soil from Inner Mongolia, China

A novel bacterial strain, designated MHJ-10J^T, was isolated from a soil sample obtained from a grassland in Inner Mongolia, China. MHJ-10J^T strain could grow at 4-37 °C (optimum: 30 °C) and pH 4-9 (optimum: pH 6), as well as in the presence of 0-6% NaCl (optimum: 1%). Cells of strain MHJ-10J^T are Gram-negative, rod-shaped, and motile. Phylogenetic analysis based on 16S rRNA gene sequences indicated that strain MHJ-10J^T was most closely related to Pseudomonas lutea OK2^T (98.5% 16S rRNA gene sequence similarity). The values of the average nucleotide identities (ANI) and digital DNA-DNA hybridization (dDDH) between strain MHJ-10J^T and its related species were all below 80.5% and 24.4%, respectively, which are significantly lower than the thresholds of 95% for ANI and 70% for DDH for species delineation. The genomic G + C content of the MHJ-10J^T strain is 64.8 mol%. Based on the phenotypic, genotypic, chemotaxonomic, and phylogenetic analyses, strain MHJ-10J^T can be assigned to the genus Pseudomonas. In this study, we propose that strain MHJ-10J^T be classified as a novel species belonging to the genus Pseudomonas with the species name Pseudomonas pratensis sp. nov. The type strain of the proposed novel species is MHJ-10J^T (= KCTC 82206^T = CGMCC 17322^T).

Vibrio areninigrae as a pathogenic bacterium in a crustacean

The occurrence of infectious diseases poses a significant threat to the aquaculture industry worldwide. Therefore, characterization of potentially harmful pathogens is one of the most important strategies to control disease outbreaks. In the present study, we investigated for the first time the pathogenicity of two Vibrio species, Vibrio metschnikovii, a foodborne pathogen that causes fatalities in humans, and Vibrio areninigrae, a bacteria isolated from black sand in Korea, using a crustacean model, the signal crayfish Pacifastacus leniusculus. Mortality challenges indicated that injection of V. metschnikovii (10⁸ CFU/crayfish) has a mortality percentage of 22% in crayfish. In contrast, injection of P. leniusculus with 10⁸ or 10⁷ CFU of V. areninigrae resulted in 100% mortality within one and two days post-injection, respectively. V. areninigrae was successfully re-isolated from hepatopancreas of infected crayfish and caused 100% mortality when reinjected into new healthy crayfish. As a consequence of this infection, histopathological analysis revealed nodule formation in crayfish hepatopancreas, heart, and gills, as well as sloughed cells inside hepatopancreatic tubules and atrophy. Moreover, extracellular crude products (ECP's) were obtained from V. areninigrae in order to investigate putative virulence factors. In vivo challenges with ECP's caused >90% mortalities within the first 24 h. In vitro challenges with ECP's of hemocytes induced cytotoxicity of hemocytes within the first hour of exposure. These findings represent the first report that V. areninigrae is a highly pathogenic bacterium that can cause disease in crustaceans. On the contrary, V. metschnikovii could not represent a threat for freshwater crayfish.

Antimicrobial resistance in Aeromonas species isolated from aquatic environments in Brazil

AIM

The current study was conducted to determine the antimicrobial resistance profile and genetic relatedness of Aeromonas sp. isolated from healthcare and urban effluents, wastewater treatment plant (WWTP) and river water.

METHODS AND RESULTS

We detected the presence of genes conferring resistance to β-lactam, quinolone and aminoglycoside. Multilocus sequence typing was carried out to differentiate the strains, and multilocus phylogenetic analysis was used to identify the species. A total of 28 cefotaxime-resistant Aeromonas sp. strains were identified, harbouring uncommon Guiana-extended-spectrum (GES)-type β-lactamases (GES-1, GES-5, GES-7 and GES-16). Multidrug-resistant Aeromonas sp. were found in hospital wastewater, WWTP and sanitary effluent, and A. caviae was identified as the most prevalent species (85·7%).

CONCLUSION

The release of untreated healthcare effluents, presence of antimicrobials in the environment, in addition to multidrug-resistant Aeromonas sp., are all potential factors for the spread of resistance.

SIGNIFICANCE AND IMPACT OF THE STUDY

We identified a vast repertoire of antimicrobial resistance genes (ARG) in Aeromonas sp. from diverse aquatic ecosystems, including those that encode enzymes degrading broad-spectrum antimicrobials widely used to treat healthcare-associated infections. Hospital and sanitary effluents serve as potential sources of bacteria harbouring ARG and are a threat to public health.

Isolation of Harveyi clade Vibrio spp. collected in aquaculture farms: How can the identification issue be addressed?

Aquaculture is a fast growing industry with its development hampered by bacterial diseases. Vibriosis caused by Harveyi clade strains is known for causing heavy loss especially in shrimp aquaculture farms. For farm treatment and pathogen spread management, veterinarians and researchers need reliable bacterial identification tools. A range of identification methods have been presented for Vibrio spp. in recent literature but little feedback on their performance have been made available to this day. This study aims at comparing Vibrio spp. identification methods and providing guidance on their use. Fifty farms were sampled and bacterial colonies were isolated using specific culture media before microscopic analysis and genomic profiling using ERIC-PCR. A preliminary identification step was carried out using MALDI-ToF mass spectrometry. Four methods were compared for strain identification on 14 newly isolated Harveyi clade Vibrio spp. strains: whole genome sequencing (digital DNA DNA Hybridization (dDDH)), 5 MLSA schemes, ferric uptake regulation (fur) and lecithin-dependent haemolysin (ldh) single gene based identification methods. Apart from dDDH which is a reference method, no technique could identify all the isolates to the species level. The other tested techniques allowed a faster, cheaper but sub genus clade identification which can be interesting when absolute precision is not required. In this regard, MALDI-ToF and fur based identification seemed especially promising.

Multilocus Genotyping Reveals New Molecular Markers for Differentiating Distinct Genetic Lineages among "Candidatus Phytoplasma Solani" Strains Associated with Grapevine Bois Noir

Grapevine Bois noir (BN) is associated with infection by “Candidatus Phytoplasma solani” (CaPsol). In this study, an array of CaPsol strains was identified from 142 symptomatic grapevines in vineyards of northern, central, and southern Italy and North Macedonia. Molecular typing of the CaPsol strains was carried out by analysis of genes encoding 16S rRNA and translation elongation factor EF-Tu, as well as eight other previously uncharacterized genomic fragments. Strains of tuf-type a and b were found to be differentially distributed in the examined geographic regions in correlation with the prevalence of nettle and bindweed. Two sequence variants were identified in each of the four genomic segments harboring hlyC, cbiQ-glyA, trxA-truB-rsuA, and rplS-tyrS-csdB, respectively. Fifteen CaPsol lineages were identified based on distinct combinations of sequence variations within these genetic loci. Each CaPsol lineage exhibited a unique collective restriction fragment length polymorphism (RFLP) pattern and differed from each other in geographic distribution, probably in relation to the diverse ecological complexity of vineyards and their surroundings. This RFLP-based typing method could be a useful tool for investigating the ecology of CaPsol and the epidemiology of its associated diseases. Phylogenetic analyses highlighted that the sequence variants of the gene hlyC, which encodes a hemolysin III-like protein, separated into two clusters consistent with the separation of two distinct lineages on the basis of tufB gene sequences. Alignments of deduced full protein sequences of elongation factor-Tu (tufB gene) and hemolysin III-like protein (hlyC gene) revealed the presence of critical amino acid substitutions distinguishing CaPsol strains of tuf-type a and b. Findings from the present study provide new insights into the genetic diversity and ecology of CaPsol populations in vineyards.

Diverse Horizontally-Acquired Gene Clusters Confer Sucrose Utilization to Different Lineages of the Marine Pathogen Photobacterium damselae subsp. damselae

The ability to metabolize sucrose is a variable trait within the family Vibrionaceae. The marine bacterium Photobacterium damselae subsp. damselae (Pdd), pathogenic for marine animals and humans, is generally described as negative for sucrose utilization (Scr⁻). Previous studies have reported sucrose-utilizing isolates (Scr⁺), but the genetic basis of this variable phenotype remains uncharacterized. Here, we carried out the genome sequencing of five Scr⁺ and two Scr⁻Pdd isolates and conducted a comparative genomics analysis with sixteen additional Pdd genomes sequenced in previous studies. We identified two different versions of a four-gene cluster (scr cluster) exclusive of Scr⁺ isolates encoding a PTS system sucrose-specific IIBC component (scrA), a fructokinase (scrK), a sucrose-6-phosphate hydrolase (scrB), and a sucrose operon repressor (scrR). A scrA deletion mutant did not ferment sucrose and was impaired for growth with sucrose as carbon source. Comparative genomics analyses suggested that scr clusters were acquired by horizontal transfer by different lineages of Pdd and were inserted into a recombination hot-spot in the Pdd genome. The incongruence of phylogenies based on housekeeping genes and on scr genes revealed that phylogenetically diverse gene clusters for sucrose utilization have undergone extensive horizontal transfer among species of Vibrio and Photobacterium.

Delineating the key virulence factors and intraspecies divergence of Vibrio harveyi via whole-genome sequencing

Vibrio harveyi is one of the major pathogens in aquaculture. To identify the key virulence factors affecting pathogenesis of V. harveyi towards fish, we conducted a field investigation for three representative fish farms infected with V. harveyi. Multilocus sequence typing (MLST) and whole-genome sequencing were conducted to delineate the phylogenetic relationship and genetic divergence of V. harveyi. A total of 25 V. harveyi strains were isolated from the diseased fish and groundwater and were subtyped into 12 sequence types by MLST. Five virulence genes, mshB, pilA, hutR, ureB, and ureG, were variably presented in the sequenced strains. The virulence gene profiles strongly correlated with the distinct pathogenicity of V. harveyi strains, with a strain harboring all five genes exhibiting the highest virulence towards fish. Phenotype assay confirmed that reduced virulence correlated with decreased motility and biofilm formation ability. Additionally, three types of type VI secretion system, namely T6SS1, T6SS2, and T6SS3, were identified in V. harveyi strains, which can be classified into six, four, and 12 subtypes, respectively. In conclusion, the results indicated that the virulence level of V. harveyi is mainly determined by the above virulence genes, which may play vital roles in environmental adaptation for V. harveyi.

Determination of the Infectious Agent of Translucent Post-Larva Disease (TPD) in Penaeus vannamei

A new emerging disease called “translucent post-larvae disease” (TPD) or “glass post-larvae disease” (GPD) of Penaeus vannamei, characterized by pale or colorless hepatopancreas and digestive tract, has become an urgent threat to the shrimp farming industry. Following this clue that treatment of an antibacterial agent could alleviate the disease, systematic investigation of the potential infectious agent of TPD was conducted using bacterial identification and artificial challenge tests to fulfill Koch’s postulates. A dominant bacterial isolate, Vp-JS20200428004-2, from the moribund individuals was isolated and identified as Vibrio parahaemolyticus based on multi-locus sequence analysis. However, Vp-JS20200428004-2 differed from the V. parahaemolyticus that caused typical acute hepatopancreatic necrosis disease. Immersion challenge tests revealed that Vp-JS20200428004-2 could cause 100% mortality within 40 h at a dose of 1.83 × 10⁶ CFU/mL, and experimental infected shrimp showed similar clinical signs of TPD. The Vp-JS20200428004-2 could be re-isolated and identified from the experimental infected individuals. Moreover, histopathological analysis of diseased samples indicated that Vp-JS20200428004-2 caused severe necrosis and sloughing of epithelial cells of the hepatopancreas and midgut in shrimp individuals both naturally and experimentally infected. Our present results indicated that Vp-JS20200428004-2 is a highly virulent infectious agent associated with the TPD and deserves further attention.

Depuration processes affect the Vibrio community in the microbiota of the Manila clam, Ruditapes philippinarum

As filter-feeders, bivalve molluscs accumulate Vibrio into edible tissues. Consequently, an accurate assessment of depuration procedures and the characterization of the persistent Vibrio community in depurated shellfish represent a key issue to guarantee food safety in shellfish products. The present study investigated changes in the natural Vibrio community composition of the Ruditapes philippinarum microbiota with specific focus on human pathogenic species. For this purpose, the study proposed a MLSA-NGS approach (rRNA 16S, recA and pyrH) for the detection and identification of Vibrio species. Clam microbiota were analysed before and after depuration procedures performed in four depuration plants, using culture-dependent and independent approaches. Microbiological counts and NGS data revealed differences in terms of both contamination load and Vibrio community between depuration plants. The novel MLSA-NGS approach allowed for a clear definition of the Vibrio species specific to each depuration plant. Specifically, depurated clam microbiota showed presence of human pathogenic species. Ozone treatments and the density of clams in the depuration tank probably influenced the level of contamination and the Vibrio community composition. The composition of Vibrio community specific to each plant should be carefully evaluated during the risk assessment to guarantee a food-safe shellfish-product for the consumer.

Pseudomonas glycinae sp. nov. isolated from the soybean rhizosphere

Strains MS586T and MS82, which are aerobic, Gram-negative, rod-shaped, and polar-flagellated bacteria, were isolated from the soybean rhizosphere in Mississippi. Taxonomic positions of MS586T and MS82 were determined using a polyphasic approach. 16S rRNA gene sequence analyses of the two strains showed high pairwise sequence similarities (>98%) to some Pseudomonas species. Analysis of the concatenated 16S rRNA, rpoB, rpoD, and gyrB gene sequences indicated that the strains belonging to the Pseudomonas koreensis subgroup (SG) shared the highest similarity with Pseudomonas kribbensis strain 46-2T . Analyses of average nucleotide identity (ANI), genome-to-genome distance, delineated MS586T and MS82 from other species within the genus Pseudomonas. The predominant quinone system of the strain was ubiquinone 9 (Q-9), and the DNA G+C content was 60.48 mol%. The major fatty acids were C16:0 , C17:0 cyclo, and the summed features 3 and 8 consisting of C16:1 ω7c/C16:1 ω6c and C18:1 ω7c/C18:1 ω6c, respectively. The major polar lipids were phosphatidylglycerol, phosphatidylethanolamine, and diphosphatidylglycerol. Based on these data, it is proposed that strains MS586T and MS82 represent a novel species within the genus Pseudomonas. The proposed name for the new species is Pseudomonas glycinae, and the type strain is MS586T (accession NRRL B-65441 = accession LMG 30275).

What drives changes in the virulence and antibiotic resistance of Vibrio harveyi in the South China Sea?

To understand the driving environmental factors in changes of bacterial virulence and antibiotic resistance, we determined the prevalence, antibiotic resistance and antibiotic resistance and virulence genes of Vibrio harveyi isolated from diseased marine fish in south coastal China. We isolated 2, 52 and 53 V. harveyi strains from Fujian, Hainan and Guangdong, respectively, and identified them by multilocus sequence analysis of 16S rRNA-toxR_Vh -rctB. Nine typical virulence genes were represented at a higher average in Hainan (7.39 ± 0.24) than in Guangdong (6.91 ± 0.28). Five atypical virulence genes were detected in some isolates. In particular, flaC and vvh were detected in more than 60% of isolates. Their average number was significantly higher in Hainan (2.30 ± 0.20) than in Guangdong (1.70 ± 0.10). Multidrug resistance was widespread with an average resistance to 4.57 ± 0.18 of 15 antibiotics. Both the average number of antibiotic resistance and antibiotic resistance genes were higher in Hainan (5.25 ± 0.27 and 1.11 ± 0.15, respectively) than in Guangdong (3.87 ± 0.21 and 0.75 ± 0.10, respectively). This study demonstrated that there were more virulence genes and greater drug resistance in Hainan than in Guangdong, suggesting that warmer temperature and antibiotics pollutants probably enhance antibiotic resistance and bacterial infection.

High diversity of Vibrio spp. associated with different ecological niches in a marine aquaria system and description of Vibrio aquimaris sp. nov

The aim of the study was to characterise the diversity and niche-specific colonization of Vibrio spp. in a marine aquaria system by a cultivation-dependent approach. A total of 53 Vibrio spp. isolates were cultured from different ecological niches in a marine aquarium including microplastic (MP) and sandy sediment particles (12 weeks after added sterile to the system), detritus, and the surrounding aquarium water. Based on the 16S rRNA gene sequence phylogeny and multilocus sequence analysis (MLSA) the isolates were assigned to seven different phylotypes. Six phylotypes were identified by high probability to the species level. The highest phylotype diversity was cultured from detritus and water (six out of seven phylotypes), while only two phylotypes were cultured from MP and sediment particles. Genomic fingerprinting indicated an even higher genetic diversity of Vibrio spp. at the strain (genotype) level. Again, the highest diversity of genotypes was recovered from detritus and water while only few partially particle-type specific genotypes were cultured from MP and sediment particles. Phylotype V-2 formed an independent branch in the MLSA tree and could not be assigned to a described Vibrio species. Isolates of this phylotype showed highest 16S rRNA gene sequence similarity to type strains of Vibrio japonicus (98.5%) and Vibrio caribbeanicus (98.4%). A representative isolate, strain THAF100^T, was characterised by a polyphasic taxonomic approach and Vibrio aquimaris sp. nov., with strain THAF100^T (=DSM 109633^T=LMG 31434^T=CIP 111709^T) as type strain, is proposed as novel species.

Bacterial Exposure Mediates Developmental Plasticity and Resistance to Lethal Vibrio lentus Infection in Purple Sea Urchin (Strongylocentrotus purpuratus) Larvae

Exposure to and colonization by bacteria during development have wide-ranging beneficial effects on animal biology but can also inhibit growth or cause disease. The immune system is the prime mediator of these microbial interactions and is itself shaped by them. Studies using diverse animal taxa have begun to elucidate the mechanisms underlying the acquisition and transmission of bacterial symbionts and their interactions with developing immune systems. Moreover, the contexts of these associations are often confounded by stark differences between "wild type" microbiota and the bacterial communities associated with animals raised in conventional or germ-free laboratories. In this study, we investigate the spatio-temporal kinetics of bacterial colonization and associated effects on growth and immune function in larvae of the purple sea urchin (Strongylocentrotus purpuratus) as a model for host-microbe interactions and immune system development. We also compare the host-associated microbiota of developing embryos and larvae raised in natural seawater or exposed to adult-associated bacteria in the laboratory. Bacteria associated with zygotes, embryos, and early larvae are detectable with 16S amplicon sequencing, but 16S-FISH indicates that the vast majority of larval bacterial load is acquired after feeding begins and is localized to the gut lumen. The bacterial communities of laboratory-cultured embryos are significantly less diverse than the natural microbiota but recapitulate its major components (Alphaproteobacteria, Gammaproteobacteria, and Bacteroidetes), suggesting that biologically relevant host-microbe interactions can be studied in the laboratory. We also demonstrate that bacterial exposure in early development induces changes in morphology and in the immune system. In the absence of bacteria, larvae grow larger at the 4-arm stage. Additionally, bacteria-exposed larvae are significantly more resistant to lethal infection with the larva-associated pathogen Vibrio lentus suggesting that early exposure to high levels of microbes, as would be expected in natural conditions, affects the immune state in later larvae. These results expand our knowledge of microbial influences on early sea urchin development and establish a model in which to study the interactions between the developing larval immune system and the acquisition of larval microbiota.

A New High Throughput Sequencing Assay for Characterizing the Diversity of Natural Vibrio Communities and Its Application to a Pacific Oyster Mortality Event

The Vibrio genus is notable for including several pathogens of marine animals and humans, yet characterization of Vibrio diversity using routine 16S rRNA sequencing methods is often constrained by poor resolution beyond the genus level. Here, a new high throughput sequencing approach targeting the heat shock protein (hsp60) as a phylogenetic marker was developed to more precisely discriminate members of the Vibrio genus in environmental samples. The utility of this new assay was tested using mock communities constructed from known dilutions of Vibrio isolates. Relative to standard and Vibrio-specific 16S rRNA sequencing assays, the hsp60 assay delivered high levels of fidelity with the mock community composition at the species level, including discrimination of species within the Vibrio harveyi clade. This assay was subsequently applied to characterize Vibrio community composition in seawater and delivered substantially improved taxonomic resolution of Vibrio species compared to 16S rRNA analysis. Finally, this assay was applied to examine patterns in the Vibrio community within oysters during a Pacific oyster mortality event. In these oysters, the hsp60 assay identified species-level Vibrio community shifts prior to disease onset, pinpointing V. harveyi as a putative pathogen. Given that shifts in the Vibrio community can precede, cause, and follow disease onset in numerous marine organisms, there is a need for an accurate high throughput assay for defining Vibrio community composition in natural samples. This Vibrio-centric hsp60 sequencing assay offers the potential for precise high throughput characterization of Vibrio diversity, providing an enhanced platform for dissecting Vibrio dynamics in the environment.

Prevalence, antimicrobial susceptibility and plasmid profiling of Vibrio spp. isolated from cultured groupers in Peninsular Malaysia

BACKGROUND

Numerous prevalence studies of Vibrio spp. infection in fish have been extensively reported worldwide, including Malaysia. Unfortunately, information on the prevalence of Vibrio spp. in groupers (Epinephelus spp.) is limited. In this study, groupers obtained from nine farms located at different geographical regions in Malaysia were sampled for the presence of pathogenic Vibrio spp. and their susceptibility profiles against seven antibiotics.

RESULTS

Out of 270 grouper samples, 195 (72%) were detected with the presence of Vibrio spp. Vibrio communis showed highest prevalence in grouper (28%), followed by V. parahaemolyticus (25%), V. alginolyticus (19%), V. vulnificus (14%), V. rotiferianus (3%), Vibrio sp. (3%), V. campbellii (2%), V. mytili (2%), V. furnissii (2%), V. harveyi (1%), V. tubiashii (1%), V. fluvialis (0.3%) and V. diabolicus (0.3%). Assessment on the antibiotic susceptibility profiles of the Vibrio spp. revealed that majority of the isolates were susceptible to tetracycline, streptomycin, erythromycin and bacitracin, but resistance to ampicillin, penicillin G and vancomycin. The mean MAR index of the Vibrio isolates was 0.51, with 85% of the isolates showed MAR index value of higher than 0.2. Results indicate that the Vibrio spp. were continuously exposed to antibiotics. Furthermore, the plasmid profiles of Vibrio spp. showed that 38.7% of the isolates harbored plasmid with molecular weight of more than 10 kb, while 61.3% were without plasmid. During curing process, Vibrio spp. lost their plasmid, but remained resistant to ampicillin, penicillin G, bacitracin and vancomycin while a few isolates remained resistant to erythromycin, streptomycin and tetracycline. The results suggested that the resistance to antibiotics in isolated Vibrio spp. might be due to chromosomal and plasmid borne.

CONCLUSIONS

This study demonstrates the prevalence of Vibrio spp. in groupers and the distribution of multidrug resistance strains that could be of concern to the farmers in Malaysia. In addition, data from this study can be further used in fish disease management plan.

A modified culture medium for improved isolation of marine vibrios

Marine Vibrio members are of great interest for both ecological and biotechnological research, which often relies on their isolation. Whereas many efforts have been made for the detection of food‐borne pathogenic species, much less is known about the performances of standard culture media toward environmental vibrios. We show that the isolation/enumeration of marine vibrios using thiosulfate‐citrate‐bile salts‐sucrose agar (TCBS) as selective medium may be hampered by the variable adaptability of different taxa to the medium, which may result even in isolation failure and/or in substantial total count underestimation. We propose a modified TCBS as isolation medium, adjusted for marine vibrios requirements, which greatly improved their recovery in dilution plate counts, compared with the standard medium. The modified medium offers substantial advantages over TCBS, providing more accurate and likely estimations of the actual presence of vibrios. Modified TCBS allowed the recovery of otherwise undetected vibrios, some of which producing biotechnologically valuable enzymes, thus expanding the isolation power toward potentially new enzyme‐producers Vibrio taxa. Moreover, we report a newly designed Vibrio‐specific PCR primers pair, targeting a unique rpoD sequence, useful for rapid confirmation of isolates as Vibrio members and subsequent genetic analyses.

Possible transmission routes of Vibrio spp. in tropical cage-cultured marine fishes

This study investigates the possible transmission routes of Vibrio spp. in a tropical cage-cultured marine fishes. Samplings of cultured Asian seabass, red snapper, hybrid grouper, wild fish, trash fish, fish fry, water and sediment samples were conducted from December 2016 to August 2017. All fish were dissected in situ and swabs were taken aseptically from the skin, eye, liver and kidney for bacterial isolation and identification. Bacterial isolation and identification from water, sediment and trash fish were also made. A total of 261 Vibrio spp. isolates recovered from the cultured, wild and fry fish, as well as from the sediment and water of the farm environment were analysed. Sequences of the pyrH gene were used to investigate the degree of relatedness and possible transmission routes existing between the isolated Vibrio spp. The population tree revealed the existence of selected Vibrio spp. that possibly transmitted between the newly introduced fish fry and wild fish into the cultured fish, while water also might possibly serves as natural transmission medium of certain Vibrio spp. in this fish farm. SIGNIFICANCE AND IMPACT OF THE STUDY: The source of transmission of Vibrio spp. into farmed marine fish remains unclear. This study highlights the possible transmission routes of Vibrio into cage-cultured marine fishes via newly introduced fish fry and wild fish. Understanding the routes of transmission of Vibrio spp. might help in controlling the disease in the near future.

Genome-informed Bradyrhizobium taxonomy: where to from here?

Bradyrhizobium is thought to be the largest and most diverse rhizobial genus, but this is not reflected in the number of described species. Although it was one of the first rhizobial genera recognised, its taxonomy remains complex. Various contemporary studies are showing that genome sequence information may simplify taxonomic decisions. Therefore, the growing availability of genomes for Bradyrhizobium will likely aid in the delineation and characterization of new species. In this study, we addressed two aims: first, we reviewed the availability and quality of available genomic resources for Bradyrhizobium. This was achieved by comparing genome sequences in terms of sequencing technologies used and estimated level of completeness for inclusion in genome-based phylogenetic analyses. Secondly, we utilized these genomes to investigate the taxonomic standing of Bradyrhizobium in light of its diverse lifestyles. Although genome sequences differed in terms of their quality and completeness, our data indicate that the use of these genome sequences is adequate for taxonomic purposes. By using these resources, we inferred a fully resolved, well-supported phylogeny. It separated Bradyrhizobium into seven lineages, three of which corresponded to the so-called supergroups known for the genus. Wide distribution of key lifestyle traits such as nodulation, nitrogen fixation and photosynthesis revealed that these traits have complicated evolutionary histories. We present the first robust Bradyrhizobium species phylogeny based on genome sequence information for investigating the evolution of this important assemblage of bacteria. Furthermore, this study provides the basis for using genome sequence information as a resource to make important taxonomic decisions, particularly at the species and genus levels.

Simulated Marine Heat Wave Alters Abundance and Structure of Vibrio Populations Associated with the Pacific Oyster Resulting in a Mass Mortality Event

Marine heat waves are predicted to become more frequent and intense due to anthropogenically induced climate change, which will impact global production of seafood. Links between rising seawater temperature and disease have been documented for many aquaculture species, including the Pacific oyster Crassostrea gigas. The oyster harbours a diverse microbial community that may act as a source of opportunistic pathogens during temperature stress. We rapidly raised the seawater temperature from 20 °C to 25 °C resulting in an oyster mortality rate of 77.4%. Under the same temperature conditions and with the addition of antibiotics, the mortality rate was only 4.3%, strongly indicating a role for bacteria in temperature-induced mortality. 16S rRNA amplicon sequencing revealed a change in the oyster microbiome when the temperature was increased to 25 °C, with a notable increase in the proportion of Vibrio sequences. This pattern was confirmed by qPCR, which revealed heat stress increased the abundance of Vibrio harveyi and Vibrio fortis by 324-fold and 10-fold, respectively. Our findings indicate that heat stress-induced mortality of C. gigas coincides with an increase in the abundance of putative bacterial pathogens in the oyster microbiome and highlights the negative consequences of marine heat waves on food production from aquaculture.