Loktanella marina sp. nov., isolated from seawater

Roseobacters in a Sea of Poly- and Paraphyly: Whole Genome-Based Taxonomy of the Family Rhodobacteraceae and the Proposal for the Split of the "Roseobacter Clade" Into a Novel Family, Roseobacteraceae fam. nov

The family Rhodobacteraceae consists of alphaproteobacteria that are metabolically, phenotypically, and ecologically diverse. It includes the roseobacter clade, an informal designation, representing one of the most abundant groups of marine bacteria. The rapid pace of discovery of novel roseobacters in the last three decades meant that the best practice for taxonomic classification, a polyphasic approach utilizing phenotypic, genotypic, and phylogenetic characteristics, was not always followed. Early efforts for classification relied heavily on 16S rRNA gene sequence similarity and resulted in numerous taxonomic inconsistencies, with several poly- and paraphyletic genera within this family. Next-generation sequencing technologies have allowed whole-genome sequences to be obtained for most type strains, making a revision of their taxonomy possible. In this study, we performed whole-genome phylogenetic and genotypic analyses combined with a meta-analysis of phenotypic data to review taxonomic classifications of 331 type strains (under 119 genera) within the Rhodobacteraceae family. Representatives of the roseobacter clade not only have different environmental adaptions from other Rhodobacteraceae isolates but were also found to be distinct based on genomic, phylogenetic, and in silico-predicted phenotypic data. As such, we propose to move this group of bacteria into a new family, Roseobacteraceae fam. nov. In total, reclassifications resulted to 327 species and 128 genera, suggesting that misidentification is more problematic at the genus than species level. By resolving taxonomic inconsistencies of type strains within this family, we have established a set of coherent criteria based on whole-genome-based analyses that will help guide future taxonomic efforts and prevent the propagation of errors.

Spatiotemporal Changes in the Bacterial Community of the Meromictic Lake Uchum, Siberia

Lake Uchum is a newly defined meromictic lake in Siberia with clear seasonal changes in its mixolimnion. This study characterized the temporal dynamics and vertical profile of bacterial communities in oxic and anoxic zones of the lake across all four seasons: October (autumn), March (winter), May (spring), and August (summer). Bacterial richness and diversity in the anoxic zone varied widely between time points. Proteobacteria was the dominant bacterial phylum throughout the oxic and anoxic zones across all four seasons. Alphaproteobacteria (Loktanella) and Gammaproteobacteria (Aliidiomarina) exhibited the highest abundance in the oxic and anoxic zone, respectively. Furthermore, there was a successional shift in sulfate-reducing bacteria (SRB) and sulfur-oxidizing bacteria in the anoxic zone across the seasons. The most dominant SRB, Desulfonatronovibrio sp., is likely one of the main producers of hydrogen sulfide (H₂S) and typically accumulates the most H₂S in winter. The representative anoxygenic phototrophic bacterial group in Lake Uchum was purple sulfur bacteria (PSB). PSB were dominant (60.76%) in summer, but only had 0.2-1.5% relative abundance from autumn to spring. Multivariate analysis revealed that the abundance of these SRB and PSB correlated to the concentration of H₂S in Lake Uchum. Taken together, this study provides insights into the relationships between changes in bacterial community and environmental features in Lake Uchum.

Loktanella acticola sp. nov., isolated from seawater

A Gram-stain-negative, aerobic, non-motile and coccoid, ovoid or rod-shaped bacterial strain, designated OISW-6^T, was isolated from seawater near Oido, a South Korean island, and subjected to a polyphasic taxonomic study. Strain OISW-6^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 OISW-6^T fell within the clade comprising the type strains of Loktanella species. Strain OISW-6^T exhibited 16S rRNA gene sequence similarity values of 97.0-98.9 % to Loktanellamaricola, Loktanellatamlensis, Loktanellarosea, Loktanellamaritima, Loktanellasediminilitoris and Loktanellalitorea, and of 94.0-96.3 % to the type strains of the other Loktanella species. Strain OISW-6^T contained Q-10 as the predominant ubiquinone and C18 : 1ω7c as the major fatty acid. The major polar lipids detected in strain OISW-6^T were phosphatidylcholine, phosphatidylglycerol and one unidentified aminolipid. The DNA G+C content of strain OISW-6^T was 57.3 mol% and its DNA-DNA relatedness values with the type strains of the six phylogenetically closely related Loktanella species were 8-25 %. Differential phenotypic properties, together with its phylogenetic and genetic distinctiveness, revealed that strain OISW-6^T is separated from recognized species of the genus Loktanella. On the basis of the data presented, strain OISW-6^T is considered to represent a novel species of the genus Loktanella, for which the name Loktanellaacticola sp. nov. is proposed. The type strain is OISW-6^T (=KCTC 52837^T=NBRC 112781^T).