Acetogenesis from CO₂ in an anoxic marine sediment

Abstract

A combination of radiotracer and pore‐water concentration measurements provide evidence for the occurrence of acetogenesis from CO 2 in anoxic marine sediments that are ordinarily dominated by sulfate reduction and methanogenesis. In a month‐long incubation experiment using sediments from Cape Lookout Bight, North Carolina, we measured H 2 and acetate concentrations and monitored the incorporation of 14 CO 2 into 14 CH 4 and 14 C‐acetate. Depletion of pore‐water sulfate resulted in a period of elevated H 2 concentrations that made acetogenic CO 2 reduction thermodynamically favorable. During this period, 14 C‐acetate was produced from 14 CO 2 at rates comparable to those 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.