Abstract

Growth of six pure cultures of methanogens was inhibited by low concentrations of dissolved acetylene (C2H2); other archaebacteria (three Halobacterium species) and several eubacteria were not similarly affected. The minimum concentration of dissolved C2H2 required to inhibit growth of Methanospirillum hungatei completely was about 8 mu;m; dissolved ethylene at 20 μm had little effect on growth. Dissolved acetylene (33 mu;m) did not alter the E h of the medium, or result in a loss in viability of M. hungatei after 16 h exposures. In anaerobic cell extracts of M. hungatei, activities of hydrogenase, NADP reductase, methyl-coenzyme M reductase and ATP hydrolase were not inhibited by C2H2 concentrations several times higher than those required for growth inhibition. The intracellular ATP content of all of the methanogens dropped dramatically on exposure to C2H2. Moreover, cells of M. hungatei and Methanobacterium bryantii on exposure to C2H2 lost their ability to maintain a transmembrane pH gradient. We suggest that exposure to C2H2 results in a decline in methanogen functions which require a H+-flux, including ATP synthesis, Ni2+ uptake and methanogenesis.

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