AUTHOR=Bayraktarov Elisa , Price Roy E., Ferdelman Timothy G., Finster Kai 

TITLE=The pH and pCO2 dependence of sulfate reduction in shallow-sea hydrothermal CO2 – venting sediments (Milos Island, Greece)

JOURNAL=Frontiers in Microbiology

VOLUME=4

YEAR=2013

URL=https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2013.00111

DOI=10.3389/fmicb.2013.00111

ISSN=1664-302X

ABSTRACT=<p>Microbial sulfate reduction (SR) is a dominant process of organic matter mineralization in sulfate-rich anoxic environments at neutral pH. Recent studies have demonstrated SR in low pH environments, but investigations on the microbial activity at variable pH and CO<sub>2</sub> partial pressure are still lacking. In this study, the effect of pH and pCO<sub>2</sub> on microbial activity was investigated by incubation experiments with radioactive <sup>35</sup>S targeting SR in sediments from the shallow-sea hydrothermal vent system of Milos, Greece, where pH is naturally decreased by CO<sub>2</sub> release. Sediments differed in their physicochemical characteristics with distance from the main site of fluid discharge. Adjacent to the vent site (<italic>T</italic> ~40–75°C, pH ~5), maximal sulfate reduction rates (SRR) were observed between pH 5 and 6. SR in hydrothermally influenced sediments decreased at neutral pH. Sediments unaffected by hydrothermal venting (<italic>T</italic> ~26°C, pH ~8) expressed the highest SRR between pH 6 and 7. Further experiments investigating the effect of pCO<sub>2</sub> on SR revealed a steep decrease in activity when the partial pressure increased from 2 to 3 bar. Findings suggest that sulfate reducing microbial communities associated with hydrothermal vent system are adapted to low pH and high CO<sub>2</sub>, while communities at control sites required a higher pH for optimal activity.</p>