Hydrogen‐using bacteria in a methanogenic acetate enrichment culture

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Abstract
In a study of the anaerobic utilization of acetate, an enrichment culture of sewage sludge organisms was initiated with calcium acetate as the sole C and energy source. A mixed bacterial population became established from which 14 anaerobic species were isolated. Two isolates were methanogenic bacteria but only 1, Methanosarcina barkeri, utilized acetate as an energy source in axenic culture. The other methanogenic isolate, a Methanobacterium sp., utilized H2/CO2 but not acetate. A 3rd methanogen, which was morphologically identical to Methanothrix soehngenii, was detected in the enrichment but was not obtained in monoculture. 2-Bromoethanesulfonate, a specific inhibitor of methanogenesis, completely inhibited the enrichment at a concentration of 10 .mu.mol/l. Addition of H2, formate or methanol to the enrichment did not affect the rate of methanogenesis. An H2-utilizing Desulfovibrio sp. was also isolated from the enrichment.