Thalassospira aquimaris sp. nov. and Winogradskyella marincola sp. nov. two marine bacteria isolated from an agar-degrading co-culture

Two novel Gram-stain-negative, aerobic, and non-motile strains, designated FZY0004T and YYF002T, were isolated from an agar-degrading co-culture, which was obtained from seawater of the intertidal zone of Yancheng City, the Yellow Sea of China. Strain FZY0004T optimally grew at 28 °C, pH 7.0, and 2-6% NaCl, while strain YYF002T optimally grew at 28 °C, pH 7.5, and 2-4% NaCl. Strain FZY0004T possessed Q-9 as the major respiratory quinone, and its major fatty acids (> 10%) were summed feature 8 (C18:1 ω7c), C16:0, and summed feature 3 (C16:1 ω7c/C16:1 ω6c). The polar lipids identified in strain FZY0004T were phosphatidylethanolamine (PE), phosphatidylglycerol (PG), and several unidentified phospholipids (PL) and lipids (L). On the other hand, strain YYF002T had MK-6 as the predominant respiratory quinone and its major fatty acids consisted of iso-C15:0, iso-C15:1 G, and iso-C15:0 3-OH. The polar lipids identified in strain YYF002T were aminolipid (AL), PE, and several unidentified lipids. Strain FZY0004T shared 99.5% 16S rRNA gene sequence similarity and 90.1% average nucleotide identity (ANI) with T. povalilytica Zumi 95T, and strain YYF002T shared 99.2% 16S rRNA gene sequence similarity and 88.2% ANI with W. poriferorum JCM 12885T. The genomic DNA G + C contents of strains FZY0004T and YYF002T were 54.5% and 33.5%, respectively. The phylogenetic, phenotypic, and physiological characteristics permitted the distinction of the two strains from their neighbors, and we thus propose the names Thalassospira aquimaris sp. nov. (type strain FZY0004T = JCM 35895T = MCCC 1K08380T) and Winogradskyella marincola sp. nov. (type strain YYF002T = JCM 35950T = MCCC 1K08382T).

Curvivirga aplysinae gen. nov., sp. nov., a marine bacterium isolated from the sea sponge Aplysina fistularis

A Gram-stain-negative, strictly aerobic, motile bacterium, designated strain RKSG073^T, was isolated from the sea sponge Aplysina fistularis, collected off the west coast of San Salvador, The Bahamas. Cells were curved-to-spiral rods with single, bipolar (amphitrichous) flagella, oxidase- and catalase-positive, non-nitrate-reducing and required salt for growth. RKSG073^T grew optimally at 30-37 °C, pH 6-7, and with 2-3 % (w/v) NaCl. The predominant fatty acids of RKSG073^T were summed feature 8 (C_18 : 1ω6c and/or C_18 : 1ω7c) and C_16 : 0. Major isoprenoid quinones were identified as Q-10 and Q-9. Phylogenetic analyses of nearly complete 16S rRNA genes and genome sequences positioned strain RKSG073^T in a clade with its closest relative Aestuariispira insulae AH-MY2^T (92.1 % 16S rRNA gene sequence similarity), which subsequently clustered with Hwanghaeella grinnelliae Gri0909^T, Marivibrio halodurans ZC80^T and type species of the genera Kiloniella, Thalassospira and Terasakiella. The DNA G+C content calculated from the genome of RKSG073^T was 42.2 mol%. On the basis of phylogenetic distinctiveness and polyphasic analysis, here we propose that RKSG073^T (culture deposit numbers: ATCC collection = TSD-74^T, BCCM collection = LMG 29869^T) represents the type strain of a novel genus and species within the family Kiloniellaceae, order Rhodospirillales and class Alphaproteobacteria, for which the name Curvivirga aplysinae 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.

Thalassospira marina sp. nov., isolated from surface seawater

Two novel marine bacteria, designated strains CSC3H3^T and CSC1P2, were isolated from surface seawater of the South China Sea. Both strains were Gram-negative, oxidase-positive, catalase-positive, curved rods and motile. They grew at 10-40 °C, pH 5-10 and in the presence of 0-15 % (w/v) NaCl. Their 16S rRNA gene sequences were identical to each other. Phylogenetic analysis based on 16S rRNA gene sequences indicated that they belong to the genus Thalassospira, and shared 97.5-98.3 % sequence similarity to all other validly type strains of the genus Thalassospira, and the highest similarity was to the type strain Thalassospira povalilyticaZumi 95^T (98.3 %), followed by Thalassospira australica NP3b2^T (98.2 %). The digital DNA-DNA hybridization value between the two strains was 80.4 %, while the values with T. povalilyticaZumi 95^T and T. australica NP3b2^T were only 20.5-20.7 % and 20.4-20.5 %, respectively. The two strains possess similar major cellular fatty acids including C18 : 1ω7c, C16 : 0, C19 : 0ω8c cyclo, C18 : 1 2-OH and C17 : 0 cyclo. The G+C contents of the chromosomal DNA of strains CSC3H3^T and CSC1P2 were 54.6 and 54.5 mol%, respectively. The major respiratory quinone was ubiquinone 10. Phosphatidylethanolamine, phosphatidylglycerol and several unidentified phospholipids, aminolipid and lipids were present in both strains. Based on phenotypic and genotypic characteristics, the two strains represent a novel species within the genus Thalassospira, for which the name Thalassospira marina sp. nov. is proposed. The type strain is CSC3H3^T (=MCCC 1A11786^T=KCTC 62333^T).

Thalassospira indica sp. nov., isolated from deep seawater

A taxonomic study using a polyphasic approach was carried out on strain PB8BT, which was isolated from the deep water of the Indian Ocean. Cells of the bacterium were Gram-stain-negative, oxidase- and catalase-positive, curved rods and motile. Growth was observed at salinities of 0-15 % and at temperatures of 10-41°C. The isolate could reduce nitrate to nitrite and degrade Tween 80, but not degrade gelatin. Phylogenetic analysis based on 16S rRNA gene sequences indicated that strain PB8BT belonged to the genus Thalassospira, with the highest sequence similarity to the closely related type strain Thalassospira tepidiphila 1-1BT (99.7 %), followed by Thalassospira profundimaris WP0211T (99.6 %). Multilocus sequence analysis demonstrated low similarities of 94.1 and 93.7 % between strain PB8BT and the two reference type strains. Digital DNA-DNA hybridization values between strain PB8BT and the two above-mentioned type strains were, respectively, 56.3 and 55.3 %. The principal fatty acids of strain PB8BT were C18 : 1ω6c/C18 : 1ω7c, C19 : 0 cyclo ω8c and C16 : 0. The G+C content of the chromosomal DNA was 54.9 mol%. The quinone was determined to be Q-10 (100 %). Phosphatidylglycerol, phosphatidylethanolamine, and several unidentified phospholipids and lipids were present. Based on phenotypic and genotypic characteristics, strain PB8BT represents a novel species within the genus Thalassospira, for which the name Thalassospira indica sp. nov. is proposed. The type strain of the novel species is PB8BT (=MCCC 1A01103T=LMG 29620T).

Limibacillus halophilus gen. nov., sp. nov., a moderately halophilic bacterium in the family Rhodospirillaceae isolated from reclaimed land

A Gram-stain-negative, aerobic, non-motile, non-spore-forming and short rod-shaped bacterial strain, designated CAU 1121T, was isolated from reclaimed land in the Republic of Korea and its taxonomic position was investigated using a polyphasic approach. The bacterium grew optimally at 37 °C, at pH 6.5 and in the presence of 2 % (w/v) NaCl. Based on 16S rRNA gene sequence similarity, the novel isolate belonged to the family Rhodospirillaceae within the class Alphaproteobacteria and formed an independent lineage within the evolutionary radiation encompassed by the phylum Proteobacteria. Strain CAU 1121T exhibited very low levels of 16S rRNA gene sequence similarity with its phylogenetic neighbours Pelagibius litoralis (similarity, 92.5 %), Fodinicurvata fenggangensis (similarity, 91.4 %), Fodinicurvata sediminis (similarity, 90.7 %) and Tistlia consotensis (similarity, 91.0 %). Strain CAU 1121T contained ubiquinone-10 as the only respiratory quinone and C18 : 1ω7c as the major cellular fatty acid. The DNA G+C content of the strain was 65 mol%. On the basis of phylogenetic inference, and physiological and chemotaxonomic data, it is proposed that strain CAU 1121T represents a novel genus and novel species in the family Rhodospirillaceae, for which the name Limibacillus halophilus gen. nov., sp. nov. is suggested. The type strain is CAU 1121T ( = KCTC 42420T = CECT 8803T = NBRC 110928T).

Cultivation-dependent and cultivation-independent characterization of hydrocarbon-degrading bacteria in Guaymas Basin sediments

Marine hydrocarbon-degrading bacteria perform a fundamental role in the biodegradation of crude oil and its petrochemical derivatives in coastal and open ocean environments. However, there is a paucity of knowledge on the diversity and function of these organisms in deep-sea sediment. Here we used stable-isotope probing (SIP), a valuable tool to link the phylogeny and function of targeted microbial groups, to investigate polycyclic aromatic hydrocarbon (PAH)-degrading bacteria under aerobic conditions in sediments from Guaymas Basin with uniformly labeled [¹³C]-phenanthrene (PHE). The dominant sequences in clone libraries constructed from ¹³C-enriched bacterial DNA (from PHE enrichments) were identified to belong to the genus Cycloclasticus. We used quantitative PCR primers targeting the 16S rRNA gene of the SIP-identified Cycloclasticus to determine their abundance in sediment incubations amended with unlabeled PHE and showed substantial increases in gene abundance during the experiments. We also isolated a strain, BG-2, representing the SIP-identified Cycloclasticus sequence (99.9% 16S rRNA gene sequence identity), and used this strain to provide direct evidence of PHE degradation and mineralization. In addition, we isolated Halomonas, Thalassospira, and Lutibacterium sp. with demonstrable PHE-degrading capacity from Guaymas Basin sediment. This study demonstrates the value of coupling SIP with cultivation methods to identify and expand on the known diversity of PAH-degrading bacteria in the deep-sea.

Multilocus sequence analysis for assessment of phylogenetic diversity and biogeography in Thalassospira bacteria from diverse marine environments

Thalassospira bacteria are widespread and have been isolated from various marine environments. Less is known about their genetic diversity and biogeography, as well as their role in marine environments, many of them cannot be discriminated merely using the 16S rRNA gene. To address these issues, in this report, the phylogenetic analysis of 58 strains from seawater and deep sea sediments were carried out using the multilocus sequence analysis (MLSA) based on acsA, aroE, gyrB, mutL, rpoD and trpB genes, and the DNA-DNA hybridization (DDH) and average nucleotide identity (ANI) based on genome sequences. The MLSA analysis demonstrated that the 58 strains were clearly separated into 15 lineages, corresponding to seven validly described species and eight potential novel species. The DDH and ANI values further confirmed the validity of the MLSA analysis and eight potential novel species. The MLSA interspecies gap of the genus Thalassospira was determined to be 96.16–97.12% sequence identity on the basis of the combined analyses of the DDH and MLSA, while the ANIm interspecies gap was 95.76–97.20% based on the in silico DDH analysis. Meanwhile, phylogenetic analyses showed that the Thalassospira bacteria exhibited distribution pattern to a certain degree according to geographic regions. Moreover, they clustered together according to the habitats depth. For short, the phylogenetic analyses and biogeography of the Thalassospira bacteria were systematically investigated for the first time. These results will be helpful to explore further their ecological role and adaptive evolution in marine environments.