Occurrence of antibiotic-resistant bacteria in the sea surface microlayer of coastal waters in the southern North Sea

The emergence of antibiotic-resistant bacteria in coastal waters is a global health problem posing potential risks to the health of humans who depend on coastal resources. Monitoring and increased efforts are needed to maintain the health of marine ecosystems. The sea surface microlayer (SML) is poorly studied for antibiotic resistance of the inhabiting bacteria. Therefore, we examined the antibiotic resistance patterns of 41 bacterial strains isolated from the SML in a harbor in the southern North Sea. The strains are affiliated with 17 genera typically found in the marine environment. Using the disc diffusion assay, we found extensive resistance, particularly to gentamycin, kanamycin, nalidixic acid, penicillin, sulfadimidine, and streptomycin. A broth microdilution assay showed high minimum inhibitory concentrations (MICs) for most isolates for amikacin, aztreonam, ceftazidime, cefepime, minocycline, and tobramycin. Genome analysis of three strains affiliated with the genera Pseudoseohaeicola, Nereida, and Vibrio, all showing a highly resistant phenotype, revealed the presence of 57, 42, and 90 genes, respectively, associated with antibiotic resistance. Over 50 % of these genes are multidrug efflux pumps. Our study shows that the SML in anthropogenic-influenced coastal regions harbors a wide diversity of antibiotic-resistant bacteria equipped with a broad range of multidrug efflux pumps.

Identification and genomic analysis of Pseudosulfitobacter koreense sp. nov. isolated from toxin-producing dinoflagellate Alexandrium pacificum

The bacterial strain AP-MA-4^T isolated from the marine dinoflagellate Alexandrium pacificum (KCTC AG60911), was subjected to a taxonomic analysis. Cells of strain AP-MA-4^T were Gram-stain-negative, aerobic, rod-shaped, optimum growth at 20 °C, pH 7.0, in the presence of 5% (w/v) NaCl. Strain AP-MA-4^T shared the highest 16S rRNA gene sequence similarity to Pseudosulfitobacter pseudonitzschiae DSM 26824^T (98.5%), followed by Ascidiaceihabitans donghaensis RSS1-M3^T (96.3%), Pseudoseohaeicola caenipelagi BS-W13^T (95.7%), and Sulfitobacter pontiacus CHLG 10^T (95.3%). Based on 16S rRNA phylogeny, strain AP-MA-4^T is phylogenetically closely related to Pseudosulfitobacter pseudonitzschiae (type species of Pseudosulfitobacter) and could be distinguished from the type species based on their phenotypic properties. The genome length of strain AP-MA-4^T was 3.48 Mbp with a 62.9% G + C content. The average nucleotide identity (ANI) and digital DNA-DNA hybridization (dDDH) values between strain AP-MA-4 ^T and its closely related type strains were 72.2-83.3 and 18.2-27.6%, respectively. Summed feature 8 (C_18:1ω7c and/or C_18:1ω6c) was identified the major fatty acids (> 10%). Phosphatidylglycerol (PG), phosphatidylethanolamine (PE), and phospholipid (PL) were demonstrated as the major polar lipids. The major respiratory quinone is ubiquinone-10 (Q-10). Based on genotypic and phenotypic features, strain AP-MA-4^T (= KCTC 92289^T = GDMCC 1.3585^T) represents a new Pseudosulfitobacter species, in which the name Pseudosulfitobacter koreense sp. nov. is proposed.

Roseitranquillus sediminis gen. nov., sp. nov. a novel genus and species of the family Rhodobacteraceae, isolated from sediment of an Arctic fjord

A Gram-negative, aerobic, non-motile, oxidase-positive, catalase-positive, rod-shaped bacterium, designated strain MCCB 386^T was isolated from sediment samples collected from Kongsfjorden, an Arctic fjord. The strain MCCB 386^T showed growth at 4-37 °C (optimum 27°C) in the presence of 1-8% NaCl (w/v, optimum 3.5%) and at pH 6.0-8.0 (optimum pH 7.0). The major fatty acids were C_18:1ω7c (54.0%) and 11-methyl C_18:1ω7c (22.6%). The dominant respiratory quinone was Q-10. The major polar lipids comprised of phosphatidylcholine (PC), diphosphatidylglycerol (DPG), phosphatidylglycerol (PG), phosphoglycolipid (PGL), one unidentified aminolipid, two glycolipids and two unidentified lipids. The genomic G+C content of the strain MCCB 386^T was 68.1 mol%. The 16 S rRNA gene sequences based phylogenetic analysis of MCCB 386^T showed that Psychromarinibacter halotolerans YBW34^T (95.88%) is the most closely related species. In addition, overall genome relatedness indices (OGRI) of MCCB 386^T with closely related strains were lower than threshold level for species and genus delineation. The analysis of Biosynthetic Gene clusters (BGCs) revealed the potential of this strain for production of novel bioactive secondary metabolites. As per polyphasic taxonomic characterisation, strain MCCB 386^T represents a novel species of a novel genus for which the name Roseitranquillus sediminis gen. nov., sp. nov. is suggested. The type strain of the species is MCCB 386^T (= JCM 33,538^T= KACC 21,531^T).

Kangsaoukella pontilimi gen. nov., sp. nov., a new member of the family Rhodobacteraceae isolated from a tidal mudflat

A strictly aerobic, Gram-stain-negative, non-motile, ovoid- and rod-shaped bacterium, designated strain GH1-50^T, was isolated from a tidal mudflat sample collected from Dongmak seashore on Gangwha Island, Republic of Korea. The organism showed growth at 20-40 °C (optimum, 30 °C), pH 7-8 (optimum, pH 7) and 2-6  % (w/v) NaCl (optimum, 5 %). The pufLM genes were present but bacteriochlorophyll a was not detected. The major isoprenoid quinone was Q-10. The polar lipids were phosphatidylcholine, phosphatidylglycerol, phosphatidylinositol, an unidentified aminolipid and five unidentified lipids. The predominant cellular fatty acids were C_18 : 1  ω7c, C_18 : 1  ω7c 11-methyl and C_18 : 0. Phylogenetic analysis based on 16S rRNA gene sequence comparisons revealed that the isolate belonged to the family Rhodobacteraceae and was loosely associated with members of the recognized genera. The closest relative was the type strain of Pseudoruegeria marinistellae (96.8 % similarity) followed by Boseongicola aestuarii (96.4 %). Other members of the family shared 16S rRNA gene similarity values below 96.0 % to the novel isolate. The DNA G+C content calculated from the draft genome sequence was 64.0 %. The average amino acid identity, average nucleotide identity and digital DNA-DNA hybridization values between genome sequences of strain GH1-50^T and all the type strains of the recognized taxa compared were <70.0, <84.1 and <20.5 %, respectively. Based on data obtained by a polyphasic approach, strain GH1-50^T (=KCTC 72224^T=NBRC 113929^T) represents a novel species of a new genus in the family Rhodobacteraceae, for which the name Kangsaoukella pontilimi gen. nov., sp. nov. is proposed.

Analysis of 1,000+ Type-Strain Genomes Substantially Improves Taxonomic Classification of Alphaproteobacteria

The class Alphaproteobacteria is comprised of a diverse assemblage of Gram-negative bacteria that includes organisms of varying morphologies, physiologies and habitat preferences many of which are of clinical and ecological importance. Alphaproteobacteria classification has proved to be difficult, not least when taxonomic decisions rested heavily on a limited number of phenotypic features and interpretation of poorly resolved 16S rRNA gene trees. Despite progress in recent years regarding the classification of bacteria assigned to the class, there remains a need to further clarify taxonomic relationships. Here, draft genome sequences of a collection of genomes of more than 1000 Alphaproteobacteria 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 recognized as problematic long ago 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 and of a variety of genera to other families. In addition, emended descriptions are given for many species mainly involving information on DNA G+C content and (approximate) genome size, both of which are confirmed as valuable taxonomic markers. Similarly, analysis of the gene content was shown to provide valuable taxonomic insights in the class. Significant incongruities between 16S rRNA gene and whole genome trees were not found in the class. The incongruities that became obvious when comparing the results of the present study with existing classifications appeared to be caused mainly by insufficiently resolved 16S rRNA gene trees or incomplete taxon sampling. Another probable cause of misclassifications in the past is the partially low overall fit of phenotypic characters to the sequence-based tree. Even though a significant degree of phylogenetic conservation was detected in all characters investigated, the overall fit to the tree varied considerably.

Litorivita pollutaquae gen. nov., sp. nov., a marine bacterium in the family Rhodobacteraceae isolated from surface seawater of Xiamen Port, China

A Gram-stain-negative Rhodobacterales strain, designated as FSX-11^T, was isolated from surface seawater of Xiamen port in China. Strain FSX-11^T showed less than 96.5 % 16S rRNA gene sequence similarity to the type strains of species with validly published names. Phylogenetic analysis based on 16S rRNA gene sequences revealed that the novel isolate formed a distinct monophyletic clade within the family Rhodobacteriaceae and clustered distantly with the genera Thalassobius and Marivita. Cells of strain FSX-11^T were non-motile, oval-shaped and facultative anaerobic. Optimal growth occurred at 20-30 °C, at pH 7.0-8.0 and in the presence of 2-3 % NaCl (w/v). The major respiratory quinone was ubiquinone-10. Summed feature 8 (C18 : 1ω7c and/or C18 : 1ω6c), 11-methyl C18 : 1ω7c and C16 : 0 were the major fatty acids. The DNA G+C content of strain FSX-11^T was 58.7 mol%. On the basis of phylogenetic analysis, phenotypic and chemotaxonomic characteristics and 16S rRNA gene signature nucleotide patterns, strain FSX-11^T represents a novel species in a novel genus within the family Rhodobacteraceae, for which the name Litorivita pollutaquae gen. nov., sp. nov. is proposed. The type strain is FSX-11^T (=JCM 32715^T=MCCC 1K03503^T).

Rhodosalinus sediminis gen. nov., sp. nov., isolated from marine saltern

A novel Gram-stain-negative, moderately halophilic, motile, facultatively anaerobic and rod-shaped strain, designated WDN1C137^T, was isolated from a marine saltern at Wendeng, PR China. Optimal growth occurred at 40 °C, pH 7.5 and with 7.0 % (w/v) NaCl. Q-10 was the sole respiratory quinone. The major cellular fatty acids (>10.0 %) in WDN1C137^T were C18 : 1ω7c (46.2 %), cyclo C19 : 0ω8c (18.7 %) and C16 : 0 (12.3 %). The major polar lipids were phosphatidylglycerol, phosphoglycolipid, phosphatidylcholine, one unidentified glycolipid, one unidentified lipid, one unidentified aminolipid and two unidentified phospholipids. The genomic DNA G+C content was 70.9 mol%. Phylogenetic analysis based on 16S rRNA gene sequences revealed that WDN1C137^T shared the highest similarity (94.5 %) to Roseivivax jejudonensis KCTC 42110^T, followed by Roseivivax halodurans JCM 10272^T (94.2 %) and Roseivivax roseus DSM 23042^T (94.1 %). WDN1C137^T formed a separate branch from the closely related genera Roseivivax, Loktanella, Paracoccus and Cribrihabitans within the family Rhodobacteraceae, which indicated that it represented a novel genus in the phylogenetic tree. On the basis of the data from the current polyphasic study, the isolate is proposed to represent a novel species of a novel genus within the family Rhodobacteraceae, with the name Rhodosalinus sediminis gen. nov., sp. nov. The type strain of the type species is WDN1C137^T (=KCTC 52478^T=MCCC 1H00170^T).

Psychromarinibacter halotolerans gen. nov., sp. nov., isolated from seawater of the Yellow Sea

A Gram-stain-negative, strictly aerobic, motile, non-gliding, oxidase-positive, catalase-positive, rod-shaped bacterium, designated strain YBW34T, was isolated from seawater from the bottom of the Yellow Sea at station H12 (-73m in depth). Growth occurred at 10-45 °C (optimum 28 °C), in the presence of 1-12 % NaCl (w/v, optimum 4 %) and at pH 6.0-8.0 (optimum pH 7.0). The major fatty acids (>10 %) were C18 : 1 ω7c and C16 : 0. The major polar lipids comprised phosphatidylcholine, phosphatidylglycerol, phosphatidylethanolamine and three unidentified aminolipids. The major respiratory quinone was ubiquinone-10 (Q-10). The DNA G+C content of strain YBW34T was 64.2 mol%. The most closely related species was Tropicimonas isoalkanivorans JCM 14837T with 95.8 % sequence similarity in Alphaproteobacteria. It showed 16S rRNA gene sequence similarities of 93.03-95.49, 93.03-95.49 and 95.31-95.32 % to species of genera Rhodovulum, Lutimaribacter and Oceanicola, respectively. Nevertheless, strain YBW34T formed a distinct lineage in the trees which did not join the genera mentioned above in the phylogenetic dendrogram based on 16S rRNA gene sequences. The phenotypic, chemotaxonomic and phylogenetic data indicated that strain YBW34T represents a novel genus and species, for which the name Psychromarinibacter halotolerans gen. nov., sp. nov. is proposed. The type strain is YBW34T (=JCM 31462T=KCTC 52366T=MCCC 1K03203T).

Jindonia aestuariivivens gen. nov., sp. nov., isolated from a tidal flat on the south-western sea in Republic of Korea

A Gram-stain-negative, aerobic, non-flagellated, and coccoid, ovoid or rod-shaped bacterium, designated JDTF-65^T, was isolated from a tidal flat on the south-western sea in Republic of Korea. Strain JDTF-65^T grew optimally at 25°C, at pH 7.0-8.0 and in the presence of 2.0% (w/v) NaCl. Strain JDTF-65^T exhibited 16S rRNA gene sequence similarities of 97.1-97.6% to the type strains of 'Aliisedimentitalea scapharcae', Phaeobacter gallaeciensis, Phaeobacter inhibens, Leisingera aquimarina, Tropicibacter litoreus, Sulfitobacter pseudonitzschiae, and Pseudoseohaeicola caenipelagi. Phylogenetic trees based on 16S rRNA gene sequences showed that strain JDTF-65^T forms an independent lineage within the radiation enclosed by the family Rhodobacteraceae. Strain JDTF-65^T contained Q-10 as the predominant ubiquinone and C_18:1 ω7c as the major fatty acid. The major polar lipids of strain JDTF-65^T were phosphatidylcholine, phosphatidylethanolamine, phosphatidylglycerol, one unidentified aminolipid, and one unidentified lipid. The DNA G+C content of strain JDTF-65^T was 56.8 mol% and its DNA-DNA relatedness values with the type strains of the phylogenetically related species were 13-27%. Differential phenotypic properties revealed that strain JDTF-65^T is separated from representatives of some phylogenetically related taxa. On the basis of the data presented, strain JDTF-65^T represents a new genus and species within the family Rhodobacteraceae, for which the name Jindonia aestuariivivens gen. nov., sp. nov. is proposed. The type strain of Jindonia aestuariivivens is JDTF-65^T (=KCTC 52564^T =NBRC 112534^T).