AMMONIUM AND NITRITE INHIBITION OF METHANE OXIDATION BY METHYLOBACTER-ALBUS BG8 AND METHYLOSINUS-TRICHOSPORIUM OB3B AT LOW METHANE CONCENTRATIONS

Methane oxidation by pure cultures of the methanotrophs Methylobacter albus BG8 and Methylosinus trichosporium OB3b was inhibited by ammoniu m choride and sodium nitrite relative to that in cultures assayed in e ither nitrate-containing or nitrate-free medium. M. albus was generall y more sensitive to ammonium and nitrite than M. trichosporium. Both s pecies produced nitrite from ammonium; the concentrations of nitrite p roduced increased with increasing methane concentrations in the cultur e headspaces. Inhibition of methane oxidation by nitrite was inversely proportional to headspace methane concentrations, with only minimal e ffects observed at concentrations of > 500 ppm in the presence of 250 mu M nitrite. Inhibition increased with increasing ammonium at methane concentrations of 100 ppm. In the presence of 500 mu M ammonium, inhi bition increased initially with increasing methane concentrations from 1.7 to 100 ppm; the extent of inhibition decreased with methane conce ntrations of > 100 ppm. The results of this study provide new insights that explain some of the previously observed interactions among ammon ium, nitrite, methane, and methane oxidation in soils and aquatic syst ems.