Gas Metabolism Evidence in Support of the Juxtaposition of Hydrogen-Producing and Methanogenic Bacteria in Sewage Sludge and Lake Sediments

We developed new techniques to measure dissolved H(2) and H(2) consumption kinetics in anoxic ecosystems that were not dependent on headspace measurements or gas transfer-limited experimentation. These H(2) metabolism parameters were then compared with measured methane production rates, and estimates of H(2) production and interspecies H(2) transfer were made. The H(2) pool sizes were 205 and 31 nM in sewage sludge from an anaerobic digestor and in sediments (24 m) from Lake Mendota, respectively. The H(2) turnover rate constants, as determined by using in situ pool sizes and temperatures, were 103 and 31 h for sludge and sediment, respectively. The observed H(2) turnover rate accounted for only 5 to 6% of the expected H(2)-CO(2)-dependent methanogenesis in these ecosystems. Our results are in general agreement with the results reported previously and are used to support the conclusion that most of the H(2)-dependent methanogenesis in these ecosystems occurs as a consequence of direct interspecies H(2) transfer between juxtapositioned microbial associations within flocs or consortia.