Acetogenesis from CO2 in an anoxic marine sediment

A combination of radiotracer and pore-water concentration measurements provide evidence for the occurrence of acetogenesis from CO2 in anoxic marine sediments that are ordinarily dominated by sulfate reduction and methanogenesis. In a month-long incubation experiment using sediments from Cape Lookout Eight, North Carolina, we measured H-2 and acetate concentrations and monitored the incorporation of (CO2)-C-14 into (CH4)-C-14 and C-14-acetate. Depletion of pore water sulfate resulted in a period of elevated H-2 concentrations that made acetogenic CO2 reduction thermodynamically favorable. During this period, C-14-acetate was produced from (CO2)-C-14 at rates comparable to these of methanogenesis or sulfate reduction during their respective periods of dominance in the incubation. Maintenance of elevated but constant H-2 concentrations immediately following sulfate depletion likely reflects control by acetogenic bacteria, suggesting they were the dominant consumers of H-2 during this period.