Ammonium conversion and its feedback effect on methane oxidation of Methylosinus sporium.

Ammonium (NH) is not only nitrogen source that can support methanotrophic growth, but also it can inhibit methane (CH) oxidation by competing with CH for the active site of methane monooxygenase. NH conversion and its feedback effect on the growth and activity of methanotrophs were evaluated with Methylosinus sporium used as a model methanotroph. Nitrogen sources could affect the CH-derived carbon distribution, which varied with incubation time and nitrogen concentrations. More CH-derived carbon was incorporated into biomass in the media with NH-N, compared to nitrate-nitrogen (NO-N), as sole nitrogen source at the nitrogen concentrations of 10-18 mmol L. Although ammonia (NH) oxidation activity of methanotrophs was considerably lower, only accounting for 0.01-0.06% of CH oxidation activity in the experimental cultures, NH conversion could lead to the pH decrease and toxic intermediates accumulation in the their habits. Compared with NH, nitrite (NO) accumulation in the NH conversion of methanotroph had stronger inhibition on its activity, especially the joint inhibition of NO accumulation and the pH decrease during the NH-N conversion. These results suggested that more attention should be paid to the feedback effects of NH conversion by methanotrophs to understand effects of NH on CH oxidation in the environments.

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