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

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Abstract
We developed new techniques to measure dissolved H2 and H2 consumption kinetics in anoxic ecosystems that were not dependent on headspace measurements or gas transfer-limited experimentation. These H2 metabolism parameters were then compared with measured methane production rates, and estimates of H2 production and interspecies H2 transfer were made. The H2 pool sizes were 205 and 31 nM in sewage sludge from an anaerobic digestor and in sediments (24 m) from Lake Mendota, respectively. The H2 turnover rate constants, as determined by using in situ pool sizes and temperatures, were 103 and 31 h-1 for sludge and sediment, respectively. The observed H2 turnover rate accounted for only 5 to 6% of the expected H2-CO2-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 H2-dependent methanogenesis in these ecosystems occurs as a consequence of direct interspecies H2 transfer between juxtapositioned microbial associations within flocs or consortia.