Microbial activity in deep marine sediments: does pressure make the difference?

We attempted to evaluate the effects of high hydrostatic pressure on microbial heterotrophic activity in deep marine sediments from the Atlantic Ocean. We investigated the potential respiration rates (acetate/glucose oxidation to CO2) in oxic sediments recovered from up to ∼4500 m water depth. Incubations were performed at ambient pressure and at near in situ pressure (∼40-45 MPa) with sediments stored at ambient pressure and at in situ pressure. Potential respiration rates in sediments stored at ambient pressure were lower when measured at in situ pressure than when measured at ambient pressure, independently of the substrate used. It appears that the pressure of storage is critical since potential respiration rates of sediments stored at in situ pressure were higher than in the counterpart sediments stored at ambient pressure.