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

Abstract

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 −1 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.