Growth and Phylogenetic Properties of Novel Bacteria Belonging to the Epsilon Subdivision of the Proteobacteria Enriched from Alvinella pompejana and Deep-Sea Hydrothermal Vents

Recent molecular characterizations of microbial communities from deep-sea hydrothermal sites indicate the predominance of bacteria belonging to the epsilon subdivision of Proteobacteria (epsilon Proteobacteria). Here, we report the first enrichments and characterizations of four epsilon Proteobacteria that are directly associated with Alvinella pompejana, a deep sea hydrothermal vent polychete, or with hydrothermal vent chimney samples. These novel bacteria were moderately thermophilic sulfur-reducing heterotrophs growing on formate as the energy and carbon source. In addition, two of them (Am-H and Ex-18.2) could grow on sulfur lithoautrotrophically using hydrogen as the electron donor. Optimal growth temperatures of the bacteria ranged from 41 to 45°C. Phylogenetic analysis of the small-subunit ribosomal gene of the two heterotrophic bacteria demonstrated 95% similarity to Sulfurospirillum arcachonense, an epsilon Proteobacteria isolated from an oxidized marine surface sediment. The autotrophic bacteria grouped within a deeply branching clade of the epsilon Proteobacteria, to date composed only of uncultured bacteria detected in a sample from a hydrothermal vent along the mid-Atlantic ridge. A molecular survey of various hydrothermal vent environments demonstrated the presence of two of these bacteria (Am-N and Am-H) in more than one geographic location and habitat. These results suggest that certain epsilon Proteobacteria likely fill important niches in the environmental habitats of deep-sea hydrothermal vents, where they contribute to overall carbon and sulfur cycling at moderate thermophilic temperatures.

近期针对深海热液喷口环境微生物群落的分子表征研究表明，隶属于变形菌门ε-变形菌亚门（Epsilon Proteobacteria）的细菌为优势类群。本研究首次完成了4株ε-变形菌亚门细菌的富集培养与表征，这些菌株分别与深海热液喷口多毛类动物庞贝虫（Alvinella pompejana）或热液喷口烟囱样体样本直接相关。这些新型细菌为中度嗜热性硫还原异养菌，可利用甲酸盐作为能量与碳源进行生长。此外，其中两株（Am-H与Ex-18.2）可利用氢气作为电子供体，通过化能硫自养途径生长。该类细菌的最适生长温度范围为41℃至45℃。对两株异养菌的小亚基核糖体基因进行系统发育分析后发现，其与从氧化型海洋表层沉积物中分离得到的ε-变形菌亚门菌株Sulfurospirillum arcachonense的序列相似性达95%。化能自养菌株聚类于ε-变形菌亚门的一个深部分支演化支中，该演化支目前仅包含在大西洋中脊热液喷口样本中发现的未培养细菌。针对多种热液喷口环境的分子普查显示，其中两株细菌（Am-N与Am-H）在多个地理区域与生境中均有分布。上述研究结果表明，部分ε-变形菌亚门细菌很可能在深海热液喷口生境中占据关键生态位，并在中度嗜热条件下参与整体的碳循环与硫循环过程。