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


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