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

Ammonium (NH4(+)) is not only nitrogen source that can support methanotrophic growth, but also it can inhibit methane (CH4) oxidation by competing with CH4 for the active site of methane monooxygenase. NH4(+) 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 CH4-derived carbon distribution, which varied with incubation time and nitrogen concentrations. More CH4-derived carbon was incorporated into biomass in the media with NH4(+)-N, compared to nitrate-nitrogen (NO3(-)-N), as sole nitrogen source at the nitrogen concentrations of 10-18 mmol L(-1). Although ammonia (NH3) oxidation activity of methanotrophs was considerably lower, only accounting for 0.01-0.06% of CH4 oxidation activity in the experimental cultures, NH4(+) conversion could lead to the pH decrease and toxic intermediates accumulation in the their habits. Compared with NH4(+), nitrite (NO2(-)) accumulation in the NH4(+) conversion of methanotroph had stronger inhibition on its activity, especially the joint inhibition of NO2(-) accumulation and the pH decrease during the NH4(+)-N conversion. These results suggested that more attention should be paid to the feedback effects of NH4(+) conversion by methanotrophs to understand effects of NH4(+) on CH4 oxidation in the environments.