A continuous culture bioreactor was developed to enrich for nitrate and sulfate reducing thermophiles under in situ deep-sea pressures. The ultimate objective of this experimental design was to be able to study microbial activities at chemical and physical conditions relevant to seafloor hydrothermal vents. Sulfide, sulfate and oxide minerals from sampled seafloor vent-chimney structures [East Pacific Rise (9°46′N)] served as source mineral and microbial inoculum for enrichment culturing using nitrate and sulfate-enriched media at 70 and 90°C and 250 bars. Changes in microbial diversity during the continuous reaction flow were monitored using denaturing gradient gel electrophoresis (DGGE) of PCR amplified 16S rRNA gene fragments. Time series changes in fluid chemistry were also monitored throughout the experiment to assess the feedback between mineral-fluid reaction and metabolic processes. Data indicate a shift from the dominance of epsilon Proteobacteria in the initial inoculum to the several Aquificales-like phylotypes in nitrate-reducing enrichment media and Thermodesulfobacteriales in the sulfate-reducing enrichment media. Methanogens were detected in the original sulfide sample and grew in selected sulfate-enriched experiments. Microbial interactions with anhydrite and pyrrhotite in the chimney material resulted in measurable changes in fluid chemistry despite a fluid residence time only 75 min in the reactor. Changes in temperature rather than source material resulted in greater differences in microbial enrichments and mediated geochemical reactions.
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Acknowledgments This research was support by National Science Foundation grants to Anna-Louise Reysenbach (OCE-0083134 and OCE-0242038) and William Seyfried (OCE-0083151). The authors thank Karen Von Damm for inviting us on her research cruise to the East Pacific Rise (supported by OCE-0327126). Thanks also to the Alvin team and the crew of the RV Altantis.
- Continuous culture
- In situ pressure