Multilocus sequence analysis of putative Vibrio mediterranei strains and description of Vibrio thalassae sp. nov

Novel metagenomics analysis of stony coral tissue loss disease

Stony coral tissue loss disease (SCTLD) has devastated coral reefs off the coast of Florida and continues to spread throughout the Caribbean. Although a number of bacterial taxa have consistently been associated with SCTLD, no pathogen has been definitively implicated in the etiology of SCTLD. Previous studies have predominantly focused on the prokaryotic community through 16S rRNA sequencing of healthy and affected tissues. Here, we provide a different analytical approach by applying a bioinformatics pipeline to publicly available metagenomic sequencing samples of SCTLD lesions and healthy tissues from four stony coral species. To compensate for the lack of coral reference genomes, we used data from apparently healthy coral samples to approximate a host genome and healthy microbiome reference. These reads were then used as a reference to which we matched and removed reads from diseased lesion tissue samples, and the remaining reads associated only with disease lesions were taxonomically classified at the DNA and protein levels. For DNA classifications, we used a pathogen identification protocol originally designed to identify pathogens in human tissue samples, and for protein classifications, we used a fast protein sequence aligner. To assess the utility of our pipeline, a species-level analysis of a candidate genus, Vibrio, was used to demonstrate the pipeline's effectiveness. Our approach revealed both complementary and unique coral microbiome members compared to a prior metagenome analysis of the same dataset.

Vibrio methylphosphonaticus sp. nov., a methylphosphonate-decomposing bacterium isolated from surface seawater in the Xisha Islands, PR China

A Gram-stain-negative, facultative anaerobic, methylphosphonate-decomposing, motile by a polar flagellum and rod-shaped marine bacterium, designated S4B1T, was isolated from the surface seawater collected from the Yongle Atoll (Xisha Islands, PR China). The pairwise alignment showed the highest sequence similarity of 97.5 and 96.6 % to Vibrio aestuarianus subsp. cardii 12_122_3T3T and Vibrio atypicus HHS02T, respectively. Phylogenetic analysis based on 16S rRNA gene and the phylogenomic analysis of single-copy genes showed that strain S4B1T belonged to the genus Vibrio and formed a close branch with Vibrio qingdaonensis ZSDZ65T. Growth of strain S4B1T occurred at 4-30 °C (optimum, 28 °C), at pH 6.0-8.0 (optimum, pH 7.0) and in the presence of 2-7 % (w/v) NaCl (optimum, 3 %). The predominant fatty acids (>10 %) were C16 : 0, iso-C16 : 0 and summed feature 3 (C16 : 1  ω7c or/and C16 : 1  ω6c). The DNA G+C content of the assembled genomic sequence was 44.3 mol%. Average nucleotide identity (ANI) values between S4B1T and its reference species were lower than the threshold for species delineation (95-96 %), in which its highest ANI value with V. qingdaonensis ZSDZ65T was 87.0 %. In silico DNA-DNA hybridization further showed that strain S4B1T had less than 70 % similarity to its relatives. On the basis of the polyphasic evidence, strain S4B1T is proposed to represent a novel species of the genus Vibrio, for which the name Vibrio methylphosphonaticus sp. nov. is proposed. The type strain is S4B1T (=KCTC 92311T=MCCC 1K06168T).

Multipathogen infections and multifactorial pathogenesis involved in noble pen shell (Pinna nobilis) mass mortality events: Background and current pathologic approaches

Disease outbreaks in several ecologically or commercially important invertebrate marine species have been reported in recent years all over the world. Mass mortality events (MMEs) have affected the noble pen shell (Pinna nobilis), causing its near extinction. Our knowledge of the dynamics of diseases affecting this species is still unclear. Early studies investigating the causative etiological agent focused on a novel protozoan parasite, Haplosporidium pinnae, although further investigations suggested that concurrent polymicrobial infections could have been pivotal in some MMEs, even in the absence of H. pinnae. Indeed, moribund specimens collected during MMEs in Italy, Greece, and Spain demonstrated the presence of a bacteria from within the Mycobacterium simiae complex and, in some cases, species similar to Vibrio mediterranei. The diagnostic processes used for investigation of MMEs are still not standardized and require the expertise of veterinary and para-veterinary pathologists, who could simultaneously evaluate a variety of factors, from clinical signs to environmental conditions. Here, we review the available literature on mortality events in P. nobilis and discuss approaches to define MMEs in P. nobilis. The proposed consensus approach should form the basis for establishing a foundation for future studies aimed at preserving populations in the wild.

Characterization of Vibrio mediterranei Isolates as Causative Agents of Vibriosis in Marine Bivalves

Marine bivalves include species important globally for aquaculture and estuary ecology. However, epizootics of variable etiologies often pose a threat to the marine fishery industry and ecosystem by causing significant mortalities in related species. One of such diseases is larval vibriosis caused by bacteria of the genus Vibrio, which frequently occurs and causes mass mortalities in bivalve larvae and juveniles in hatcheries. During a mass mortality of razor clam, Sinonovacula constricta, juveniles in a shellfish hatchery in 2019, Vibrio mediterranei was identified as a dominant bacterial species in diseased animals and their rearing water. In this study, we selected and characterized 11 V. mediterranei isolates and studied their pathogenicity to the larvae and juveniles of S. constricta and Crossostrea sikamea. We found that V. mediterranei isolates showed various degrees of pathogenicity to the experimental animals by immersion. Injection of the extracellular products (ECPs) of the strains into clam juveniles resulted in similar pathogenicity with strain immersion. Furthermore, the measurements of enzyme activity suggested the existence of virulence factors in the ECPs of disease-causing V. mediterranei strains. Additionally, proteomic analysis revealed that more than 700 differentially expressed proteins were detected in the ECPs among V. mediterranei strains with different levels of virulence, and the higher expressed proteins in the ECPs of highly virulent strains were involved mainly in the virulence-related pathways. This research represented the first characterization of the V. mediterranei strains as causative agents for larval bivalve vibriosis. The mechanisms underlying the pathogenicity and related strain variability are under further study. IMPORTANCE In the marine environment, Vibrio members have a significant impact on aquatic organisms. Larval vibriosis, caused by bacteria of the genus Vibrio, often poses a threat to the marine fishery industry and ecosystem by causing the mortality of bivalves. However, the emerging pathogens of larval vibriosis in bivalves have not been explored fully. Vibrio mediterranei, the dominant bacterium isolated from moribund clam juveniles in a mortality event, may be responsible for the massive mortality of bivalve juveniles and vibriosis occurrence. Thus, it is necessary to study the pathogenic mechanisms of V. mediterranei to bivalve larvae. We found that V. mediterranei was the pathogen of larval bivalve vibriosis, and its extracellular products contributed a critical role for virulence in juveniles. This research is the first report of V. mediterranei as a causative agent for vibriosis in bivalve juveniles. Our results provide valuable information for understanding the pathogenic mechanism of V. mediterranei to bivalve larvae.

Transcriptomic identification of key genes in Pacific oysters Crassostrea gigas responding to major abiotic and biotic stressors

Oysters are commercially important intertidal filter-feeding species. Mass mortality events of oysters often occur due to environmental stresses, such as exposure to fluctuating temperatures, salinity, and air, as well as to metal pollution and pathogen infection. Here, RNA-seq data were used to identify shared and specific responsive genes by differential gene expression analysis and weighted gene co-expression network analysis. A total of 18 up-regulated and 10 down-regulated shared responsive genes were identified corresponding to five different stressors. Total 27 stressor-specific genes for temperature, 11 for salinity, 80 for air exposure, 51 for metal pollution, and 636 for Vibrio mediterranei pathogen stress were identified in oysters. Elongin-β was identified as a crucial gene for thermal stress response. Some HSP70s were determined to be shared responsive genes while others were specific to thermal tolerance. The proteins encoded by these stress-related genes should be further investigated to characterize their physiological functions. In addition, the uncharacterized proteins and ncRNAs that were identified may be involved in species-specific stress-response and regulatory mechanisms. This study identified specific genes related to stressors relevant to oyster cultivation. These findings provide useful information for new selective breeding strategies using a data driven method.

Draft Genome Sequence of Vibrio mediterranei Strain CyArs1

Here, we report on the draft genome sequence of Vibrio mediterranei strain CyArs1, isolated from the marine sponge Cinachyrella sp. Genome annotation revealed multiple genomic features, including eukaryotic-like repeat protein- and multidrug resistance-encoding genes, potentially involved in symbiotic relationships with the sponge host.

Vibrio mediterranei, a potential emerging pathogen of marine fauna: investigation of pathogenicity using a bacterial challenge in Pinna nobilis and development of a species-specific PCR

AIMS

Extreme mortality events affecting Pinna nobilis, some associated to Vibrio mediterranei, have depleted many populations of this bivalve. The objective of this study was to demonstrate pathogenicity of V. mediterranei in the host P. nobilis by performing a bacterial challenge in P. nobilis to understand if V. mediterranei has specific virulence in this host. To assist this objective, a secondary objective was to develop a species-specific DNA diagnostic test.

METHODS AND RESULTS

Pinna nobilis collected from local bays were used in a challenge experiment with V. mediterranei (strain IRTA18-108). The virulence in the host background of P. nobilis was demonstrated at doses of 10³ CFUs per animal. An alignment of published Vibrio sp. atpA sequences was used to design V. mediterranei-specific primers. Furthermore, data mining of published literature and V. mediterranei genomes identified multiple virulence-related genes (vir genes) from which specific primers were designed for PCR detection of selected genes.

CONCLUSION

Vibrio mediterranei strain IRTA18-108 is pathogenic in the host P. nobilis. The virulence genes sod, rtx and mshA were identified in this strain. Temperatures of 24°C or higher appear to trigger onset of virulence. Sensitivity and specificity of the Vm atpA PCR is useful for diagnosis of Vibriosis in shellfish.

SIGNIFICANCE AND IMPACT OF THE STUDY

The presence of previously described virulence genes have been confirmed in this strain. The specific Vm atpA PCR assay will aid management of future epizootics of this emerging pathogen of aquatic fauna, and improve surveillance capabilities for mortality events where Vibrios are suspect.

AHL-lactonase expression in three marine emerging pathogenic Vibrio spp. reduces virulence and mortality in brine shrimp (Artemia salina) and Manila clam (Venerupis philippinarum)

Bacterial infectious diseases produced by Vibrio are the main cause of economic losses in aquaculture. During recent years it has been shown that the expression of virulence genes in some Vibrio species is controlled by a population-density dependent gene-expression mechanism known as quorum sensing (QS), which is mediated by the diffusion of signal molecules such as N-acylhomoserine lactones (AHLs). QS disruption, especially the enzymatic degradation of signalling molecules, known as quorum quenching (QQ), is one of the novel therapeutic strategies for the treatment of bacterial infections. In this study, we present the detection of AHLs in 34 marine Vibrionaceae strains. Three aquaculture-related pathogenic Vibrio strains, V. mediterranei VibC-Oc-097, V. owensii VibC-Oc-106 and V. coralliilyticus VibC-Oc-193 were selected for further studies based on their virulence and high production of AHLs. This is the first report where the signal molecules have been characterized in these emerging marine pathogens and correlated to the expression of virulence factors. Moreover, the results of AHL inactivation in the three selected strains have been confirmed in vivo against brine shrimps (Artemia salina) and Manila clams (Venerupis philippinarum). This research contributes to the development of future therapies based on AHL disruption, the most promising alternatives for fighting infectious diseases in aquaculture.

Vibrio barjaei sp. nov., a new species of the Mediterranei clade isolated in a shellfish hatchery

Seven isolates were obtained from different culture stages of carpet shell clam (Ruditapes decussatus) reared in a bivalve hatchery (Galicia, NW Spain). Three groups were differentiated by genotyping techniques and phenotypic profiles and representative trains were selected to further taxonomic studies. These strains were studied by a polyphasic approach and in basis of the phylogenetic analysis based on concatenated sequences of the five housekeeping genes ftsZ, gyrB, pyrH, recA and rpoA formed a tight group into the Mediterranei clade of the genus Vibrio. Percentages of genomic resemblance, including average nucleotide identity, in silico genome-to-genome comparison and wet DNA-DNA hybridization between the type strain and the closest relatives Vibrio mediterranei and Vibrio thalassae were below of the proposed boundaries for the definition of species. The novel isolates could be also differentiated from the related taxa on the basis of several phenotypic traits and fatty acid profiles. Results obtained support the description of a novel species into the Mediterranei clade, for which the name Vibrio barjaei sp. nov. is proposed, with strain 3062^T (=CECT 9090^T=CAIM 1921T^T=LMG 29358^T) as the type strain.

Vibrio sonorensis sp. nov. isolated from a cultured oyster Crassostrea gigas

Strain CAIM 1076^T was isolated from a cultured oyster Crassostrea gigas in Puerto Peñasco, Sonora state, México. The strain was taxonomically characterised by means of a genomic approach, comprising 16S rRNA gene sequence analysis, multilocus sequence analysis (MLSA), the DNA G+C content and whole genome analyses (ANI and GGDC), and by phenotypic characterisation. Strain CAIM 1076^T was found to be catalase and oxidase positive, and cells were observed to be motile and facultative anaerobic. Analysis of the almost-complete 16S rRNA gene sequence placed this strain within the genus Vibrio; closely related species were Vibrio maritimus, Vibrio variabilis, Vibrio proteolyticus, and Vibrio nigripulchritudo with similarity values of 98.9, 98.5, 98.1, and 98.0 %, respectively. MLSA of six housekeeping genes (ftsZ, gapA, gyrB, recA, rpoA and topA) was performed with the closely related species. A draft genome sequence of strain CAIM 1076^T was obtained. The DNA G+C content of this strain was determined to be 44.5 mol %. The genomic similarity values with V. maritimus were 71.6 % (ANIb), 85.1 % (ANIm) and a GGDC value of 20.3 ± 2.3 %; with V. variabilis the genomic similarities were 71.8 % (ANIb), 85.4 % (ANIm) and 20.0 ± 2.3 % (GGDC); with V. proteolyticus, 71.6 % (ANIb), 84.1 % (ANIm) and 18.8 ± 2.2 % (GGDC); and with V. nigripulchritudo, 70.8 % (ANIb), 84.9 % (ANIm) and 20.5 ± 2.3 % (GGDC). These ANI and GGDC values are below the thresholds for the delimitation of prokaryotic species, i.e., 95-96 and 70 %, respectively. Phenotypic characters also showed differences with the closely related species analysed. The results presented here support the description of a novel species, for which the name Vibrio sonorensis sp. nov. is proposed, with strain CAIM 1076^T (=CECT 9100^T, =DSM 102190^T) as the type strain.

The Role of Vibrios in Diseases of Corals

The tissue, skeleton, and secreted mucus of corals supports a highly dynamic and diverse community of microbes, which play a major role in the health status of corals such as the provision of essential nutrients or the metabolism of waste products. However, members of the Vibrio genus are prominent as causative agents of disease in corals. The aim of this chapter is to review our understanding of the spectrum of disease effects displayed by coral-associated vibrios, with a particular emphasis on the few species where detailed studies of pathogenicity have been conducted. The role of Vibrio shilonii in seasonal bleaching of Oculina patagonica and the development of the coral probiotic hypothesis is reviewed, pointing to unanswered questions about this phenomenon. Detailed consideration is given to studies of V. coralliilyticus and related pathogens and changes in the dominance of vibrios associated with coral bleaching. Other Vibrio-associated disease syndromes discussed include yellow band/blotch disease and tissue necrosis in temperate gorgonian corals. The review includes analysis of the role of enzymes, resistance to oxidative stress, and quorum sensing in virulence of coral-associated vibrios. The review concludes that we should probably regard most-possibly all-vibrios as "opportunistic" pathogens which, under certain environmental conditions, are capable of overwhelming the defense mechanisms of appropriate hosts, leading to rapid growth and tissue destruction.

Vibrio renipiscarius sp. nov., isolated from cultured gilthead sea bream (Sparus aurata)

Two strains of Gram-negative, facultatively anaerobic, slightly halophilic bacteria, isolated from healthy gilthead sea bream (Sparus aurata) cultured in Spanish Mediterranean fish farms, were different from their closest relatives, Vibrio scophthalmi and V. ichthyoenteri, by phenotypic, phylogenetic and genomic standards. The strains were negative for decarboxylase tests and lacked extracellular hydrolytic activities, but were able to ferment d-mannitol, sucrose, cellobiose and d-gluconate, among other carbohydrates. The major cellular fatty acids were C16: 1 and C16: 0, in agreement with other species of the genus Vibrio. Their 16S rRNA gene sequences were 98.4 and 97.2 % similar to those of the type strains of V. scophthalmi and V. ichthyoenteri, and the similarities using other housekeeping genes (ftsZ, rpoD, recA, mreB and gyrB) and indices of genomic resemblance (average nucleotide identity and estimated DNA–DNA hybridization) between the isolates and those type strains were clearly below intraspecific levels, supporting the recognition of the strains as members of a separate novel species. Thus, we propose the name Vibrio renipiscarius sp. nov., with DCR 1-4-2T ( = CECT 8603T = KCTC 42287T) as the type strain.

Multilocus Sequence Analysis of the redefined clade Scophthalmi in the genus Vibrio

A Multilocus Sequence Analysis (MLSA) was performed on members of the Scophthalmi clade in the genus Vibrio, including type and reference strains of the species V. scophthalmi, V. ichthyoenteri, and 39 strains phenotypically identified as Vibrio ichthyoenteri-like, with the aim of better defining boundaries between these two closely related, fish-associated species. The type strain of V. ponticus, recently added to the clade Scophthalmi, was also included. The study was based on partial sequences of the protein-coding housekeeping genes rpoD, mreB, recA, ftsZ, and gyrB, and the 16S rRNA. While the 16S rRNA gene-based trees were unable to pull apart members of V. scophthalmi or V. ichthyoenteri, both the other individual gene trees and the trees obtained from the five-genes concatenated sequences were able to consistently differentiate four subclades within the main clade, corresponding to the bona fide V. scophthalmi, V. ichthyoenteri, and two small ones that may represent a new species each. The best genes to differentiate V. scophthalmi from V. ichthyoenteri were rpoD, recA, and mreB. Vibrio ponticus failed to associate to the clade in the MLSA and in most single gene trees for which it should not be considered part of it. In this study we also confirm using genomic indexes that V. ichthyoenteri and V. scophthalmi are two separate species.

Bioinformatic genome comparisons for taxonomic and phylogenetic assignments using Aeromonas as a test case

Prokaryotic taxonomy is the underpinning of microbiology, as it provides a framework for the proper identification and naming of organisms. The “gold standard” of bacterial species delineation is the overall genome similarity determined by DNA-DNA hybridization (DDH), a technically rigorous yet sometimes variable method that may produce inconsistent results. Improvements in next-generation sequencing have resulted in an upsurge of bacterial genome sequences and bioinformatic tools that compare genomic data, such as average nucleotide identity (ANI), correlation of tetranucleotide frequencies, and the genome-to-genome distance calculator, or in silico DDH (isDDH). Here, we evaluate ANI and isDDH in combination with phylogenetic studies using Aeromonas, a taxonomically challenging genus with many described species and several strains that were reassigned to different species as a test case. We generated improved, high-quality draft genome sequences for 33 Aeromonas strains and combined them with 23 publicly available genomes. ANI and isDDH distances were determined and compared to phylogenies from multilocus sequence analysis of housekeeping genes, ribosomal proteins, and expanded core genes. The expanded core phylogenetic analysis suggested relationships between distant Aeromonas clades that were inconsistent with studies using fewer genes. ANI values of ≥96% and isDDH values of ≥70% consistently grouped genomes originating from strains of the same species together. Our study confirmed known misidentifications, validated the recent revisions in the nomenclature, and revealed that a number of genomes deposited in GenBank are misnamed. In addition, two strains were identified that may represent novel Aeromonas species.

Improvements in DNA sequencing technologies have resulted in the ability to generate large numbers of high-quality draft genomes and led to a dramatic increase in the number of publically available genomes. This has allowed researchers to characterize microorganisms using genome data. Advantages of genome sequence-based classification include data and computing programs that can be readily shared, facilitating the standardization of taxonomic methodology and resolving conflicting identifications by providing greater uniformity in an overall analysis. Using Aeromonas as a test case, we compared and validated different approaches. Based on our analyses, we recommend cutoff values for distance measures for identifying species. Accurate species classification is critical not only to obviate the perpetuation of errors in public databases but also to ensure the validity of inferences made on the relationships among species within a genus and proper identification in clinical and veterinary diagnostic laboratories.

List of new names and new combinations previously effectively, but not validly, published

The purpose of this announcement is to effect the valid publication of the following effectively published new names and new combinations under the procedure described in the Bacteriological Code (1990 Revision). Authors and other individuals wishing to have new names and/or combinations included in future lists should send three copies of the pertinent reprint or photocopies thereof, or an electronic copy of the published paper to the IJSEM Editorial Office for confirmation that all of the other requirements for valid publication have been met. It is also a requirement of IJSEM and the ICSP that authors of new species, new subspecies and new combinations provide evidence that types are deposited in two recognized culture collections in two different countries. It should be noted that the date of valid publication of these new names and combinations is the date of publication of this list, not the date of the original publication of the names and combinations. The authors of the new names and combinations are as given below. Inclusion of a name on these lists validates the publication of the name and thereby makes it available in the nomenclature of prokaryotes. The inclusion of a name on this list is not to be construed as taxonomic acceptance of the taxon to which the name is applied. Indeed, some of these names may, in time, be shown to be synonyms, or the organisms may be transferred to another genus, thus necessitating the creation of a new combination.