Niche differentiation among mat-forming, sulfide-oxidizingbacteria at cold seeps of the Nile Deep Sea Fan (EasternMediterranean Sea)

摘要

Sulfidic muds of cold seeps on the Nile Deep Sea Fan (NDSF) are populated by different types of mat-formingsulfide-oxidizing bacteria. The predominant sulfide oxidizers of three different mats were identified by microscopicand phylogenetic analyses as (i) Arcobacter species producing cotton-ball-like sulfur precipitates, (ii) largefilamentous sulfur bacteria including Beggiatoa species, and (iii) single, spherical Thiomargarita species. High resolutionin situ microprofiles revealed different geochemical settings selecting for the different mat types. Arcobactermats occurred where oxygen and sulfide overlapped above the seafloor in the bottom water interface.Filamentous sulfide oxidizers were associated with steep gradients of oxygen and sulfide in the sediment. Adense population of Thiomargarita was favored by temporarily changing supplies of oxygen and sulfide in thebottom water. These results indicate that the decisive factors in selecting for different mat-forming bacteriawithin one deep-sea province are spatial or temporal variations in energy supply. Furthermore, the occurrence ofArcobacter spp.-related 16S rRNA genes in the sediments below all three types of mats, as well as on top of brinelakes of the NDSF, indicates that this group of sulfide oxidizers can switch between different life modes dependingon the geobiochemical habitat setting.