Oxidation rate of thiosulfate and elemental sulfur in the Black Sea

Oxidation rate of 35S-thiosulfate under simulated natural conditions and abundance of thiosulfate-oxidizing bacteria in a redox zone of the Black Sea are lower during winter and spring than in summer, especially in halistatic regions. Oxidation of thiosulfate under natural conditions is performed chiefly by lithotropic thionic bacteria, whose activity is limited by low temperatures. Adding thiosulfate and readily available organic matter to water samples from the redox zone and raising temperature of water stimulated activity of heterotrophic thiosulfate-oxidizing bacteria. Oxidation of elemental sulfur tagged with 35S apparently invovled two stages: abiotic oxidation of thiosulfate and subsequent bacterial oxidation of thiosulfate to sulfate.

Porewater concentrations, pH, single cell number, anaerobic oxidation of methane (AOM) rate, sulfate reduction (SR) rate of samples during METEOR cruise M76/3b at the REGAB cold seep site from the West African margin in 2008

The giant pockmark REGAB (West African margin, 3160 m water depth) is an active methane-emitting cold seep ecosystem, where the energy derived from microbially mediated oxidation of methane supports high biomass and diversity of chemosynthetic communities. Bare sediments interspersed with heterogeneous chemosynthetic assemblages of mytilid mussels, vesicomyid clams and siboglinid tubeworms form a complex seep ecosystem. To better understand if benthic bacterial communities reflect the patchy distribution of chemosynthetic fauna, all major chemosynthetic habitats at REGAB were investigated using an interdisciplinary approach combining porewater geochemistry, in situ quantification of fluxes and consumption of methane, as well bacterial community fingerprinting. This study revealed that sediments populated by different fauna assemblages show distinct biogeochemical activities and are associated with distinct sediment bacterial communities. The methane consumption and methane effluxes ranged over one to two orders of magnitude across habitats, and reached highest values at the mussel habitat, which hosted a different bacterial community compared to the other habitats. Clam assemblages had a profound impact on the sediment geochemistry, but less so on the bacterial community structure. Moreover, all clam assemblages at REGAB were restricted to sediments characterized by complete methane consumption in the seafloor, and intermediate biogeochemical activity. Overall, variations in the sediment geochemistry were reflected in the distribution of both fauna and microbial communities; and were mostly determined by methane flux.