Leibniz Institute for Baltic Sea Research Warnemünde, Rostock, Germany.
mBio. 2013 May 28;4(3):e00569-12. doi: 10.1128/mBio.00569-12.
The verrucomicrobial subdivision 2 class Spartobacteria is one of the most abundant bacterial lineages in soil and has recently also been found to be ubiquitous in aquatic environments. A 16S rRNA gene study from samples spanning the entire salinity range of the Baltic Sea indicated that, in the pelagic brackish water, a phylotype of the Spartobacteria is one of the dominating bacteria during summer. Phylogenetic analyses of related 16S rRNA genes indicate that a purely aquatic lineage within the Spartobacteria exists. Since no aquatic representative from the Spartobacteria has been cultured or sequenced, the metabolic capacity and ecological role of this lineage are yet unknown. In this study, we reconstructed the genome and metabolic potential of the abundant Baltic Sea Spartobacteria phylotype by metagenomics. Binning of genome fragments by nucleotide composition and a self-organizing map recovered the near-complete genome of the organism, the gene content of which suggests an aerobic heterotrophic metabolism. Notably, we found 23 glycoside hydrolases that likely allow the use of a variety of carbohydrates, like cellulose, mannan, xylan, chitin, and starch, as carbon sources. In addition, a complete pathway for sulfate utilization was found, indicating catabolic processing of sulfated polysaccharides, commonly found in aquatic phytoplankton. The high frequency of glycoside hydrolase genes implies an important role of this organism in the aquatic carbon cycle. Spatiotemporal data of the phylotype's distribution within the Baltic Sea indicate a connection to Cyanobacteria that may be the main source of the polysaccharide substrates.
疣微菌亚纲 2 级 Spartobacteria 是土壤中最丰富的细菌谱系之一，最近也被发现广泛存在于水生环境中。一项涵盖波罗的海整个盐度范围的样本 16S rRNA 基因研究表明，在海洋性半咸水中，Spartobacteria 的一个种型是夏季占主导地位的细菌之一。相关 16S rRNA 基因的系统发育分析表明，Spartobacteria 中存在一个纯粹的水生谱系。由于尚未培养或测序到 Spartobacteria 的水生代表，因此该谱系的代谢能力和生态作用尚不清楚。在本研究中，我们通过宏基因组学重建了丰富的波罗的海 Spartobacteria 种型的基因组和代谢潜力。通过核苷酸组成和自组织图对基因组片段进行分箱，恢复了该生物体的近完整基因组，其基因内容表明其具有需氧异养代谢。值得注意的是，我们发现了 23 种糖苷水解酶，这些酶可能允许该生物体利用多种碳水化合物，如纤维素、甘露聚糖、木聚糖、几丁质和淀粉作为碳源。此外，还发现了完整的硫酸盐利用途径，表明该生物体可以代谢硫酸化多糖，这些多糖通常存在于水生浮游植物中。糖苷水解酶基因的高频出现表明该生物体在水生碳循环中具有重要作用。该种型在波罗的海中的分布时空数据表明与蓝藻存在联系，蓝藻可能是多糖底物的主要来源。
