Hydrogenase Activity in Deeply Buried Sediments of the Arctic and North Atlantic Oceans

The goal of this study was to measure hydrogenase activity in oceanic sediments of the Lomonosov Ridge (Arctic Ocean) and of the Porcupine Seabight (North Atlantic), and to understand how its distribution varied depending on geochemical and lithological characteristics of the sediment. Hydrogenase activity was found at all sites, and absolute values and downhole distributions varied widely within and between sites. At the Lomonosov Ridge, hydrogenase was below detection in the top 190 meters of sediment, but high levels were measured in the organic carbon-rich layers below this depth. Activity at Challenger Mound, Porcupine Seabight (Site 1317) was one to two orders of magnitude higher than the upslope or downslope sites (1318 and 1316, respectively), and was higher in the mound than below the mound base. Consistent with the interpretation of hydrogenase as an indicator of microbial activity, cells were present in all hydrogenase-positive samples or in nearby horizons. Cell-specific activity values were as much as 1000 fold lower than those of cultured Clostridium pasteurianum, with the values from the highest activity sediments approaching those of C. pasteurianum more closely. This suggests that little adaptation in hydrogenase activity might be necessary to support H2 metabolism in deeply buried sediments that contain relatively high levels of substrates.