Polaribacter ponticola sp. nov., isolated from seawater, reclassification of Polaribacter undariae as a later heterotypic synonym of Polaribacter sejongensis, and emended description of Polaribacter sejongensis Kim et al. 2013

A Gram-stain-negative, yellow-pigmented, and strictly aerobic bacterium, designated as strain MSW5T, was isolated from seawater of the Yellow Sea in South Korea. The cells were non-motile rods exhibiting oxidase- and catalase-positive activities. Growth was observed at 15-25 °C (optimum, 25 °C) and pH 5.0-9.0 (optimum, pH 7.0-8.0) and in the presence of 1.0-5.0% (w/v) NaCl (optimum, 2.0%). Menaquinone-6 was the sole respiratory quinone, and iso-C15 : 0, summed feature 3 (C16 : 1  ω7c and/or C16 : 1  ω6c), iso-C15 : 0 3-OH, and C15 : 1  ω6c were the major cellular fatty acids. Major polar lipids included phosphatidylethanolamine, two unidentified aminolipids, and three unidentified lipids. Phylogenetic analyses based on 16S rRNA gene sequences and 92 concatenated core protein sequences revealed that strain MSW5T formed a distinct lineage within the genus Polaribacter. The genome of strain MSW5T was 3582 kb in size with a 29.1 mol% G+C content. Strain MSW5T exhibited the highest similarity to Polaribacter atrinae WP25T, with a 97.9% 16S rRNA gene sequence similarity. However, the average nucleotide identity and digital DNA-DNA hybridization values were 79.4 and 23.3%, respectively, indicating that strain MSW5T represents a novel species. Based on its phenotypic, chemotaxonomic, and phylogenetic characteristics, strain MSW5T is proposed to represent a novel species, with the name Polaribacter ponticola sp. nov. The type strain is MSW5T (=KACC 22340T=NBRC 116025T). In addition, whole genome sequence comparisons and phenotypic features suggested that Polaribacter sejongensis and Polaribacter undariae belong to the same species, with P. undariae proposed as a later heterotypic synonym of P. sejongensis. An emended description of Polaribacter sejongensis is also proposed.

Colwellia maritima sp. nov. and Polaribacter marinus sp. nov., isolated from seawater

Two Gram-stain-negative, catalase- and oxidase-positive, and aerobic bacteria, strains MSW7^T and MSW13^T, were isolated from seawater. Cells of strains MSW7^T and MSW13^T are motile and non-motile rods, respectively. Strain MSW7^T optimally grew at 25 °C and pH 7.0 and in the presence of 3 % (w/v) NaCl, whereas strain MSW13^T optimally grew at 25 °C and pH 6.0-7.0 and in the presence of 2 % NaCl. As the sole respiratory quinone and the major fatty acids and polar lipids, strain MSW7^T contained ubiquinone-8, C_16 : 0, C_15 : 1  ω8c, C_17 : 1  ω8c and summed feature 3 (C_16 : 1  ω7c and/or C_16 : 1  ω6c), and phosphatidylethanolamine and phosphatidylglycerol, respectively, whereas strain MSW13^T contained menaquinone-6, C_15 : 1  ω6c, iso-C_15 : 0, anteiso-C_15 : 0, and iso-C_15 : 0 3-OH, and phosphatidylethanolamine, respectively. The DNA G+C contents of strains MSW7^T and MSW13^T were 37.3 and 29.9 %, respectively. Phylogenetic analyses based on 16S rRNA gene sequences showed that strains MSW7^T and MSW13^T were most closely related to Colwellia echini A3^T and Polaribacter atrinae WP25^T with 98.8 and 98.1 % sequence similarities, respectively. The average nucleotide identity and digital DNA-DNA hybridization values between strain MSW7^T and C. echini A3^T and between strain MSW13^T and P. atrinae KACC 17473^T were 73.6 and 22.6 % and 80.4 and 23.8 %, respectively. Based on phenotypic, chemotaxonomic and phylogenetic data, strains MSW7^T and MSW13^T represent novel species of the genera Colwellia and Polaribacter, respectively, for which the names Colwellia maritima sp. nov. and Polaribacter marinus sp. nov. are proposed, respectively. The type strains of C. maritima sp. nov. and P. marinus sp. nov. are MSW7^T (=KACC 22339^T=JCM 35001^T) and MSW13^T (=KACC 22341^T=JCM 35021^T), respectively.

The microbiome of cryospheric ecosystems

The melting of the cryosphere is among the most conspicuous consequences of climate change, with impacts on microbial life and related biogeochemistry. However, we are missing a systematic understanding of microbiome structure and function across cryospheric ecosystems. Here, we present a global inventory of the microbiome from snow, ice, permafrost soils, and both coastal and freshwater ecosystems under glacier influence. Combining phylogenetic and taxonomic approaches, we find that these cryospheric ecosystems, despite their particularities, share a microbiome with representatives across the bacterial tree of life and apparent signatures of early and constrained radiation. In addition, we use metagenomic analyses to define the genetic repertoire of cryospheric bacteria. Our work provides a reference resource for future studies on climate change microbiology.

The cryosphere includes those parts of Earth where water or soil is frozen, such as snow, ice, glaciers and permafrost soils. Here, the authors present a global inventory of cryospheric microbial communities and their genetic repertoires.

Quantifying dominant bacterial genera detected in metagenomic data from fish eggs and larvae using genus-specific primers

The goal of this study was to design genus-specific primers for rapid evaluation of the most abundant bacterial genera identified using amplicon-based sequencing of the 16S rRNA gene in fish-related samples and surrounding water. Efficient genus-specific primers were designed for 11 bacterial genera including Alkalimarinus, Colwellia, Enterovibrio, Marinomonas, Massilia, Oleispira, Phaeobacter, Photobacterium, Polarbacerium, Pseudomonas, and Psychrobium. The specificity of the primers was confirmed by the phylogeny of the sequenced polymerase chain reaction (PCR) amplicons that indicated primers were genus-specific except in the case of Colwellia and Phaeobacter. Copy number of the 16S rRNA gene obtained by quantitative PCR using genus-specific primers and the relative abundance obtained by 16S rRNA gene sequencing using universal primers were well correlated for the five analyzed abundant bacterial genera. Low correlations between quantitative PCR and 16S rRNA gene sequencing for Pseudomonas were explained by the higher coverage of known Pseudomonas species by the designed genus-specific primers than the universal primers used in 16S rRNA gene sequencing. The designed genus-specific primers are proposed as rapid and cost-effective tools to evaluate the most abundant bacterial genera in fish-related or potentially other metagenomics samples.

Comparison of Alginate Utilization Pathways in Culturable Bacteria Isolated From Arctic and Antarctic Marine Environments

Alginate, mainly derived from brown algae, is an important carbon source that can support the growth of marine microorganisms in the Arctic and Antarctic regions. However, there is a lack of systematic investigation and comparison of alginate utilization pathways in culturable bacteria from both polar regions. In this study, 88 strains were isolated from the Arctic and Antarctic regions, of which 60 strains could grow in the medium with alginate as the sole carbon source. These alginate-utilizing strains belong to 9 genera of the phyla Proteobacteria and Bacteroidetes. The genomes of 26 alginate-utilizing strains were sequenced and genomic analyses showed that they all contain the gene clusters related to alginate utilization. The alginate transport systems of Proteobacteria differ from those of Bacteroidetes and there may be unique transport systems among different genera of Proteobacteria. The biogeographic distribution pattern of alginate utilization genes was further investigated. The alginate utilization genes are found to cluster according to bacterial taxonomy rather than geographic location, indicating that the alginate utilization genes do not evolve independently in both polar regions. This study systematically illustrates the alginate utilization pathways in culturable bacteria from the Arctic and Antarctic regions, shedding light into the distribution and evolution of alginate utilization pathways in polar bacteria.

Analysis of 1,000 Type-Strain Genomes Improves Taxonomic Classification of Bacteroidetes

Although considerable progress has been made in recent years regarding the classification of bacteria assigned to the phylum Bacteroidetes, there remains a need to further clarify taxonomic relationships within a diverse assemblage that includes organisms of clinical, piscicultural, and ecological importance. Bacteroidetes classification has proved to be difficult, not least when taxonomic decisions rested heavily on interpretation of poorly resolved 16S rRNA gene trees and a limited number of phenotypic features. Here, draft genome sequences of a greatly enlarged collection of genomes of more than 1,000 Bacteroidetes and outgroup type strains were used to infer phylogenetic trees from genome-scale data using the principles drawn from phylogenetic systematics. The majority of taxa were found to be monophyletic but several orders, families and genera, including taxa proposed long ago such as Bacteroides, Cytophaga, and Flavobacterium but also quite recent taxa, as well as a few species were shown to be in need of revision. According proposals are made for the recognition of new orders, families and genera, as well as the transfer of a variety of species to other genera. In addition, emended descriptions are given for many species mainly involving information on DNA G+C content and (approximate) genome size, both of which can be considered valuable taxonomic markers. We detected many incongruities when comparing the results of the present study with existing classifications, which appear to be caused by insufficiently resolved 16S rRNA gene trees or incomplete taxon sampling. The few significant incongruities found between 16S rRNA gene and whole genome trees underline the pitfalls inherent in phylogenies based upon single gene sequences and the impediment in using ordinary bootstrapping in phylogenomic studies, particularly when combined with too narrow gene selections. While a significant degree of phylogenetic conservation was detected in all phenotypic characters investigated, the overall fit to the tree varied considerably, which is one of the probable causes of misclassifications in the past, much like the use of plesiomorphic character states as diagnostic features.

Description of Polaribacter aestuariivivens sp. nov., isolated from a tidal flat

A bacterial strain, DBTF-3T, was isolated from a tidal flat of Republic of Korea. Phylogenetic trees of 16S rRNA gene sequences showed that strain DBTF-3T belonged to the genus Polaribacter. Strain DBTF-3T exhibited 16S rRNA gene sequence similarities of 97.1-98.1% to type strains of P. dokdonensis, P. haliotis, P. marinaquae, P. insulae, P. vadi, P. glomeratus, P. irgensii and P. reichenbachii, and 94.0-96.9% to those of the other Polaribacter species. DNA-DNA relatedness values of strain DBTF-3T with type strains of P. marinaquae and P. insulae were 14-19%. Average nucleotide identity and digital DNA-DNA hybridization values between strain DBTF-3T and type strains of six other Polaribacter species were 76.5-83.5% and 20.9-27.1%, respectively. Strain DBTF-3T contained MK-6 as the predominant menaquinone, and iso-C15:0, summed feature 3, iso-C15:1 G and iso-C15:0 3-OH as the major fatty acids. The major polar lipids were phosphatidylethanolamine and one unidentified lipid. Differential phenotypic properties, together with its phylogenetic and genetic distinctiveness, revealed that strain DBTF-3T is separated from Polaribacter species. On the basis of the data presented, strain DBTF-3T (= KACC 19612T = NBRC 113191T) represents a novel species of the genus Polaribacter, for which the name Polaribacter aestuariivivens sp. nov. is proposed.

Vibrio zhugei sp. nov., a moderately halophilic bacterium isolated from pickling sauce

Strain HBUAS61001^T was isolated from the pickling sauce used to make a traditional fermented food product, datoucai, in China. The strain belonged to the genus Vibrio, but was placed in a clade separate from any known Vibrio species based on the 16S rRNA gene and MLSA results. The genome consisted of two chromosomes: chromosome I was 2 901 449 bp long with a G+C content of 45.4 mol%; and chromosome II was 1 107 930 bp long with a G+C content of 45.5 mol%. The most abundant fatty acids were C16 : 0 (28.1 %), summed feature 3 (C16 : 1ω7c and/or C16 : 1ω6c, 29.4 %) and summed feature 8 (C18 : 1ω7c and/or C18 : 1ω6c, 10.1 %). The isoprenoid quinones detected were Q7 and Q8. The predominant polar lipids were diphosphatidylglycerol, phosphatidylethanolamine and phosphatidylglycerol. Strain HBUAS61001^T could grow in the presence of up to 17 % NaCl. The calculated average nucleotide identity and in silico DNA-DNA hybridization (GGDC) values of the strain against the closest related type strains were all lower than 95 and 70 %, respectively. Putative genes in the genome associated with survival under high salinity stress were identified. Based on whole genome sequence analysis and phenotypic characteristics, strain HBUAS61001^T is a new species in the genus Vibrio, and the name Vibrio zhugei (=GDMCC 1.1416^T=KCTC 62784^T) is proposed.

Polaribacter insulae sp. nov., isolated from a tidal flat

A Gram-stain-negative, aerobic, non-motile and ovoid or rod-shaped bacterial strain, designated OITF-22^T, was isolated from a tidal flat of Oido, an island of South Korea, and subjected to a polyphasic taxonomic study. Strain OITF-22^T grew optimally at 25 °C, at pH 7.0-8.0 and in the presence of 2.0-3.0 % (w/v) NaCl. The phylogenetic trees based on 16S rRNA gene sequences showed that strain OITF-22^T fell within the clade comprising the type strains of Polaribacter species. Strain OITF-22^T exhibited 16S rRNA gene sequence similarity values of 97.2-99.4 % to the type strains of Polaribacter vadi, P. haliotis, P. atrinae, P. dokdonensis, P. litorisediminis,P. reichenbachii, P. irgensii and P. marinaquae, and of 93.0-96.9 % to the type strains of the other Polaribacter species. Strain OITF-22^T contained MK-6 as the predominant menaquinone and iso-C15 : 0 and iso-C15 : 0 3-OH as the major fatty acids. The major polar lipids detected in strain OITF-22^T were phosphatidylethanolamine and one unidentified lipid. The DNA G+C content of strain OITF-22^T was 32.3 mol% and its DNA-DNA relatedness values with the type strains of the eight phylogenetically most closely related Polaribacter species were 9-32 %. Differential phenotypic properties, together with phylogenetic and genetic distinctiveness, revealed that strain OITF-22^T is separated from recognized species of the genus Polaribacter. On the basis of the data presented, strain OITF-22^T is considered to represent a novel species of the genus Polaribacter, for which the name Polaribacter insulae sp. nov. is proposed. The type strain is OITF-22^T (=KCTC 52658^T=NBRC 112706^T).

Polaribacter pacificus sp. nov., isolated from a deep-sea polymetallic nodule from the Eastern Pacific Ocean

A Gram-staining-negative, yellow-colony-forming, rod-shaped, non-flagellated and facultatively aerobic strain, designed HRA130-1T, was isolated from a deep-sea polymetallic nodule from the Pacific Clarion-Clipperton Fracture Zone (CCFZ). Phylogenetic analysis based on 16S rRNA gene sequences indicated that strain HRA130-1T belonged to the genus Polaribacter (96.3-93.2 % 16S rRNA gene sequence similarity), and exhibited 94 % 16S rRNA gene sequence similarity to Polaribacter filamentus KCTC 23135T (type species) and the highest sequence similarity to Polaribacter huanghezhanensis KCTC 32516T (96.3 %). Optimal growth occurred in the presence of 4 % (w/v) NaCl, at pH 7.0 and 16 °C. The DNA G+C content of strain HRA130-1T was 35.9 mol%. The major fatty acid was iso-C15 : 0. The predominant respiratory quinone was menaquinone-6 (MK-6). The major polar lipids were phosphatidylethanolamine, phosphatidylglycerol, one unidentified phospholipid and an unidentified aminolipid. On the basis of data from the present taxonomic study using a polyphasic approach, strain HRA130-1T represents a novel species of the genus Polaribacter, for which the name Polaribacter pacificus sp. nov. is proposed. The type strain is HRA130-1T (=KCTC 52370T=MCCC 1K03199T=JCM 31460T=CGMCC 1.15763T).

Polaribacter litorisediminis sp. nov., isolated from a tidal flat

A Gram-stain-negative, aerobic, non-motile and ovoid or rod-shaped bacterial strain, designated OITF-11T, was isolated from a tidal flat in Oido, an island of South Korea, and subjected to a polyphasic taxonomic study. Strain OITF-11T grew optimally at 25 °C, at pH 7.0-8.0 and in the presence of 2.0 % (w/v) NaCl. The phylogenetic trees based on 16S rRNA gene sequences showed that strain OITF-11T belonged to the genus Polaribacter. Strain OITF-11T exhibited 16S rRNA gene sequence similarity values of 97.4-98.1 % to Polaribacter haliotis RA4-7T, Polaribacter atrinae KACC 17473T, Polaribacter dokdonensis DSW-5T and Polaribacter marinaquae KCTC 42664T, and of 94.1-96.9 % to the type strains of the other Polaribacter species. Strain OITF-11T contained menaquinone MK-6 as the predominant menaquinone and iso-C15 : 0, iso-C15 : 1 G, iso-C15 : 0 3-OH, iso-C17 : 0 3-OH and C15 : 1ω6c as the major fatty acids. The major polar lipids detected in strain OITF-11T were phosphatidylethanolamine, phosphatidylmonomethylethanolamine and one unidentified lipid. The DNA G+C content of strain OITF-11T was 32.2 mol% and its DNA-DNA relatedness values with the type strains of P. haliotis, P. atrinae, P. dokdonensis and P. marinaquae were 14-33 %. Differential phenotypic properties, together with its phylogenetic and genetic distinctiveness, revealed that strain OITF-11T is separated from recognized species of the genus Polaribacter. On the basis of the data presented, strain OITF-11T is considered to represent a novel species of the genus Polaribacter, for which the name Polaribacter litorisediminis sp. nov. is proposed. The type strain is OITF-11T (=KCTC 52500T=NBRC 112457T).

Genome-Based Taxonomic Classification of Bacteroidetes

The bacterial phylum Bacteroidetes, characterized by a distinct gliding motility, occurs in a broad variety of ecosystems, habitats, life styles, and physiologies. Accordingly, taxonomic classification of the phylum, based on a limited number of features, proved difficult and controversial in the past, for example, when decisions were based on unresolved phylogenetic trees of the 16S rRNA gene sequence. Here we use a large collection of type-strain genomes from Bacteroidetes and closely related phyla for assessing their taxonomy based on the principles of phylogenetic classification and trees inferred from genome-scale data. No significant conflict between 16S rRNA gene and whole-genome phylogenetic analysis is found, whereas many but not all of the involved taxa are supported as monophyletic groups, particularly in the genome-scale trees. Phenotypic and phylogenomic features support the separation of Balneolaceae as new phylum Balneolaeota from Rhodothermaeota and of Saprospiraceae as new class Saprospiria from Chitinophagia. Epilithonimonas is nested within the older genus Chryseobacterium and without significant phenotypic differences; thus merging the two genera is proposed. Similarly, Vitellibacter is proposed to be included in Aequorivita. Flexibacter is confirmed as being heterogeneous and dissected, yielding six distinct genera. Hallella seregens is a later heterotypic synonym of Prevotella dentalis. Compared to values directly calculated from genome sequences, the G+C content mentioned in many species descriptions is too imprecise; moreover, corrected G+C content values have a significantly better fit to the phylogeny. Corresponding emendations of species descriptions are provided where necessary. Whereas most observed conflict with the current classification of Bacteroidetes is already visible in 16S rRNA gene trees, as expected whole-genome phylogenies are much better resolved.

American Lobsters (Homarus Americanus) not Surviving During Air Transport: Evaluation of Microbial Spoilage

Eighteen American lobsters (Homarus americanus), dead during air transport, were analysed in order to evaluate the microbial population of meat, gills and gut: no specific studies have ever been conducted so far on the microbiological quality of American lobsters’ meats in terms of spoilage microbiota. The meat samples showed very limited total viable counts, in almost all the cases below the level of 6 Log CFU/g, while higher loads were found, as expected, in gut and gills, the most probable source of contamination. These data could justify the possibility to commercialise these not-surviving subjects, without quality concerns for the consumers. Most of the isolates resulted to be clustered with type strains of Pseudoalteromonas spp. (43.1%) and Photobacterium spp. (24.1%), and in particular to species related to the natural marine environment. The distribution of the genera showed a marked inhomogeneity among the samples. The majority of the isolates identified resulted to possess proteolytic (69.3%) and lipolytic ability (75.5%), suggesting their potential spoilage ability. The maintanance of good hygienical practices, especially during the production of ready-to-eat lobsters-based products, and a proper storage could limit the possible replication of these microorganisms.

Aurantivirga profunda gen. nov., sp. nov., isolated from deep-seawater, a novel member of the family Flavobacteriaceae

A Gram-stain-negative, aerobic, proteorhodopsin-containing, orange, rod-shaped bacterium, designated SAORIC-234T, was isolated from deep seawater in the Pacific Ocean. 16S rRNA gene sequence analysis revealed that the strain could be affiliated with the family Flavobacteriaceae of the phylum Bacteroidetes and shared less than 94.6 % similarity with other species of the family with validly published names. The phenotypic characteristics of this novel isolate, such as growth properties and enzyme activities, could be differentiated from those of other species. The strain was non-motile, oxidase-positive and catalase-negative. The G+C content of the genomic DNA was determined to be 34.8 mol% and menaquinone-6 (MK-6) was the predominant isoprenoid quinone. The predominant fatty acids were iso-C15 : 0, iso-C15 : 1 G, iso-C16 : 0 3-OH, iso-C17 : 0 3-OH and iso-C15 : 0 3-OH. The major polar lipids comprised phosphatidylethanolamine, three unknown aminolipids and three unknown lipids. On the basis of the taxonomic data collected in this study, it was concluded that strain SAORIC-234T represents a novel genus and species in the family Flavobacteriaceae, for which the name Aurantivirga profunda gen. nov., sp. nov. is proposed. The type strain of the type species, Aurantivirga profunda sp. nov., is SAORIC-234T ( = NBRC 110606T = KACC 18400T).

Polaribacter undariae sp. nov., isolated from a brown alga reservoir

A Gram-stain-negative, non-flagellated, non-gliding, aerobic and rod-shaped or ovoid bacterial strain, designated W-BA7(T), was isolated from a brown alga reservoir on the South Sea in South Korea. This strain grew optimally at 25 °C, at pH 7.0-8.0 and in the presence of approximately 2.0% (w/v) NaCl. A neighbour-joining phylogenetic tree based on 16S rRNA gene sequences showed that strain W-BA7(T) belonged to the genus Polaribacter, clustering coherently with the type strain of Polaribacter sejongensis, showing 99.3% sequence similarity. Strain W-BA7(T) exhibited 16S rRNA gene sequence similarity of 93.4-98.6% to the type strains of the other species of the genus Polaribacter. Strain W-BA7(T) contained MK-6 as the predominant menaquinone and iso-C15 : 0 3-OH and anteiso-C15 : 0 as the major fatty acids. The major polar lipids of strain W-BA7(T) were phosphatidylethanolamine, three unidentified lipids, one unidentified glycolipid, one unidentified aminolipid and one unidentified aminophospholipid. The DNA G+C content of strain W-BA7(T) was 31.9 mol%, and the mean DNA-DNA relatedness with the type strains of four phylogenetically related species of the genus Polaribacter was 12-27%. Differential phenotypic properties, together with its phylogenetic and genetic distinctiveness, revealed that strain W-BA7(T) is separated from recognized species of the genus Polaribacter. On the basis of the data presented, strain W-BA7(T) is considered to represent a novel species of the genus Polaribacter, for which the name Polaribacter undariae sp. nov. is proposed. The type strain is W-BA7(T) ( =KCTC 42175(T) =CECT 8670(T)).

Niches of two polysaccharide-degrading Polaribacter isolates from the North Sea during a spring diatom bloom

Members of the flavobacterial genus Polaribacter thrive in response to North Sea spring phytoplankton blooms. We analyzed two respective Polaribacter species by whole genome sequencing, comparative genomics, substrate tests and proteomics. Both can degrade algal polysaccharides but occupy distinct niches. The liquid culture isolate Polaribacter sp. strain Hel1_33_49 has a 3.0-Mbp genome with an overall peptidase:CAZyme ratio of 1.37, four putative polysaccharide utilization loci (PULs) and features proteorhodopsin, whereas the agar plate isolate Polaribacter sp. strain Hel1_85 has a 3.9-Mbp genome with an even peptidase:CAZyme ratio, eight PULs, a mannitol dehydrogenase for decomposing algal mannitol-capped polysaccharides but no proteorhodopsin. Unlike other sequenced Polaribacter species, both isolates have larger sulfatase-rich PULs, supporting earlier assumptions that Polaribacter take part in the decomposition of sulfated polysaccharides. Both strains grow on algal laminarin and the sulfated polysaccharide chondroitin sulfate. For strain Hel1_33_49, we identified by proteomics (i) a laminarin-induced PUL, (ii) chondroitin sulfate-induced CAZymes and (iii) a chondroitin-induced operon that likely enables chondroitin sulfate recognition. These and other data suggest that strain Hel1_33_49 is a planktonic flavobacterium feeding on proteins and a small subset of algal polysaccharides, while the more versatile strain Hel1_85 can decompose a broader spectrum of polysaccharides and likely associates with algae.

Multilocus sequence analysis of the marine bacterial genus Tenacibaculum suggests parallel evolution of fish pathogenicity and endemic colonization of aquaculture systems

The genus Tenacibaculum, a member of the family Flavobacteriaceae, is an abundant component of marine bacterial ecosystems that also hosts several fish pathogens, some of which are of serious concern for marine aquaculture. Here, we applied multilocus sequence analysis (MLSA) to 114 representatives of most known species in the genus and of the worldwide diversity of the major fish pathogen Tenacibaculum maritimum. Recombination hampers precise phylogenetic reconstruction, but the data indicate intertwined environmental and pathogenic lineages, which suggests that pathogenicity evolved independently in several species. At lower phylogenetic levels recombination is also important, and the species T. maritimum constitutes a cohesive group of isolates. Importantly, the data reveal no trace of long-distance dissemination that could be linked to international fish movements. Instead, the high number of distinct genotypes suggests an endemic distribution of strains. The MLSA scheme and the data described in this study will help in monitoring Tenacibaculum infections in marine aquaculture; we show, for instance, that isolates from tenacibaculosis outbreaks in Norwegian salmon farms are related to T. dicentrarchi, a recently described species.

Polaribacter atrinae sp. nov., isolated from the intestine of a comb pen shell, Atrina pectinata

A novel Gram-staining-negative, aerobic, non-motile, yellow-to-orange carotenoid-type-pigmented and rod-shaped bacterium, designated strain WP25T, was isolated from the intestine of a comb pen shell, Atrina pectinata, which was collected from the South Sea near Yeosu in Korea. The isolate grew optimally at 20 °C, at pH 7 and with 2 % (w/v) NaCl. 16S rRNA gene sequence analysis showed that strain WP25T belonged to the genus Polaribacter in the family Flavobacteriaceae and the highest sequence similarity was shared with the type strain of Polaribacter sejongensis (98.5 %). The major cellular fatty acids were iso-C15 : 0, anteiso-C15 : 0, C15 : 1ω6c and iso-C15 : 0 3-OH. The main respiratory quinone was menaquinone MK-6. The polar lipids of strain WP25T were phosphatidylethanolamine, two unidentified aminolipids, an unidentified phospholipid and four unidentified lipids. The genomic DNA G+C content was 31.2 mol%. DNA–DNA hybridization experiments indicated <12.6 % genomic relatedness with closely related strains. Based on phylogenetic, phenotypic and genotypic analyses, strain WP25T represents a novel species in the genus Polaribacter , for which the name Polaribacter atrinae sp. nov. is proposed, with the type strain WP25T ( = KACC 17473T = JCM 19202T).

Wenyingzhuangia marina gen. nov., sp. nov., a member of the family Flavobacteriaceae isolated from a recirculating mariculture system

A Gram-stain-negative, strictly aerobic and heterotrophic bacterial strain, designed strain D1T, was isolated from a recirculating mariculture system in Tianjin, China. Its taxonomic position was determined using a polyphasic approach. Cells of strain D1T were non-flagellated short rods, 0.3–0.5 µm wide and 0.5–1.0 µm long. Growth was observed at 15–30 °C (optimum, 25 °C), at pH 5.5–9.0 (optimum, pH 6.5–7.0) and in the presence of 1–8 % (w/v) NaCl (optimum, 2–3 %). Cells contained carotenoid pigments but not flexirubin-type pigments. Strain D1T contained MK-6 as the sole menaquinone and phosphatidylethanolamine (PE) as the sole phospholipid and four unidentified lipids. The major cellular fatty acids (>10 %) were iso-C15 : 0 (23.2 %), iso-C17 : 0 3-OH (15.2 %), C16 : 1ω7c/C16 : 1ω6c (14.3 %), iso-C15 : 0 3-OH (13.5 %) and iso-C15 : 1 G (10.8 %). 16S rRNA gene sequence analyses indicated that strain D1T belonged to the family Flavobacteriaceae and showed closest phylogenetic relationship to the genus Lutibacter , with highest sequence similarity to Lutibacter aestuarii MA-My1T (92.2 %). The DNA G+C content of strain D1T was 35.9 mol%. On the basis of phenotypic, chemotaxonomic and phylogenetic data, strain D1T was considered to represent a novel species in a new genus of the family Flavobacteriaceae , for which the name Wenyingzhuangia marina gen. nov., sp. nov. is proposed. The type strain of the type species is D1T ( = CGMCC 1.12162T = JCM 18494T).

Polaribacter huanghezhanensis sp. nov., isolated from Arctic fjord sediment, and emended description of the genus Polaribacter

A Gram-negative, orange-colony-forming, aerobic and non-flagellated bacterium, designated strain SM1202(T), was isolated from marine sediment of Kongsfjorden, Svalbard. Analysis of 16S rRNA gene sequences revealed that strain SM1202(T) was phylogenetically closely related to the genus Polaribacter. It shared the highest 16S rRNA gene sequence similarity with the type strain of Polaribacter dokdonensis (94.2 %) and 92.7-93.9 % sequence similarity with type strains of other known species of the genus Polaribacter. The strain grew at 4-35 °C and with 1.0-5.0 % (w/v) NaCl. It contained iso-C15 : 0, iso-C15 : 0 3-OH, iso-C13 : 0, C15 : 0, iso-C15 : 1 G, iso-C17 : 0 3-OH and C15 : 1ω6c as predominant cellular fatty acids and menaquinone-6 (MK-6) as the major respiratory quinone. The polar lipids of strain SM1202(T) were phosphatidylethanolamine, one unidentified lipid, two unidentified aminophospholipids and one unidentified aminolipid. The genomic DNA G+C content of strain SM1202(T) was 36.4 mol%. On the basis of the data from this polyphasic taxonomic study, strain SM1202(T) represents a novel species in the genus Polaribacter of the family Flavobacteriaceae, for which the name Polaribacter huanghezhanensis sp. nov. is proposed. The type strain of Polaribacter huanghezhanensis is SM1202(T) ( = CCTCC AB 2013148(T) = KCTC 32516(T)). An emended description of the genus Polaribacter is also presented.