Niche differentiation among mat-forming, sulfide-oxidizing bacteria in chemosynthetic ecosystems of the Nile Deep Sea Fan (Eastern Mediterranean Sea)

Sulfidic muds of cold seeps on the Nile Deep Sea Fan are populated by different types of mat-forming sulfide-oxidizing bacteria. The predominant sulfide oxidizers of three different mats were identified by microscopic and phylogenetic analyses as (i) Arcobacter species producing cotton-ball-like sulfur precipitates, (ii) large filamentous sulfur bacteria including Beggiatoa species, or (iii) single, spherical cells resembling Thiomargarita species. High resolution in situ microprofiles revealed different geochemical settings selecting for different mat types. Arcobacter mats occurred where oxygen and sulfide overlapped at the bottom water interface. Filamentous sulfide oxidizers were associated with non-overlapping, steep gradients of oxygen and sulfide. A dense population of Thiomargarita was favored by temporarily changing supplies of oxygen and sulfide. These results indicate that the decisive factors in selecting for different mat-forming bacteria within one deep-sea province are spatial or temporal variations in energy supply. Furthermore, the occurrence of Arcobacter spp.-related 16S rRNA genes in the sediments below all three types of mats, as well as on top of brine lakes of the Nile Deep Sea Fan, indicates that this group of sulfide oxidizers can switch between different life modes depending on the geobiochemical habitat setting.尼罗河深海扇（Nile Deep Sea Fan）冷泉的硫化物软泥中，栖息着多种形成菌席的硫化物氧化细菌。通过显微分析与系统发育分析，可鉴定出三类不同菌席的优势硫化物氧化菌：其一为可产生棉絮状硫沉淀的弓形菌（Arcobacter）物种；其二为包含贝氏硫菌（Beggiatoa）在内的大型丝状硫细菌；其三为形态类似嗜硫珠菌（Thiomargarita）的单个球形细胞。高分辨率原位微剖面（in situ microprofiles）分析显示，不同的地球化学环境会筛选出不同的菌席类型。弓形菌菌席分布于氧与硫化物在底水界面重叠的区域；丝状硫化物氧化菌则与氧和硫化物不重叠的陡峭梯度环境相关；而嗜硫珠菌的高密度种群，则得益于氧与硫化物供给的周期性变化。上述结果表明，在同一深海区域内，筛选不同菌席形成细菌的决定性因素，是能量供给的空间或时间变异。此外，在三类菌席下方的沉积物中，以及尼罗河深海扇卤水湖顶部，均检测到与弓形菌属（Arcobacter spp.）相关的16S rRNA基因，这说明该类硫化物氧化菌可根据地球生物化学生境条件，切换不同的生活模式。