Effects of ammonia on growth and morphology of thermophilic hydrogen‐oxidizing methanogenic bacteria

The effects of ammonia on pure cultures of thermophilic hydrogen‐utilizing methanogens were studied. The bacteria used were Methanobacterium thermoautotrophicum strain ΔH, Methanobacterium thermoformicicum, a Methanogenium sp., and a putative Methanobacterium thermoautotrophicum strain BA. For all strains tested initial inhibition occurred at 3.0–4.0 g NH+4‐N/I (214–286 mM), and at approximately 6.0 NH+4‐N/I (428 mM), a 50% decrease of the growth rate was seen. At 9.0 g NH+4‐N/I (643 mM), growth of Methanobacterium thermoformicum was observed, whereas the other strains showed either very unstable growth or were totally inhibited. For some strains ammonia had a pronounced effect on cell morphology, inducing formation of large aggregates.