Effects of various parameters on carbon monoxide oxidation by ammonium oxidizers

Abstract

The effects of temperature, pH, nitrogen source, cell concentration, and the interactions between ammonium and carbon monoxide were examined with respect to the oxidation of carbon monoxide by several chemolithotrophic ammonium-oxidizing bacteria. The ammonium oxidizers Nitrosomonas europaea, Nitrosomonas sp. 4W30, a marine isolate, and Nitrosococcus oceanus were examined. All of the organisms were able to oxidize significant amounts of CO over wide ranges of temperature and pH. Ammonium at concentrations as low as 1 mg/L [Formula: see text] N initially inhibited CO oxidation in all three organisms; however, after 48 h, the presence of ammonium stimulated the CO-oxidizing ability of Nitrosomonas europaea and Nitrosomonas sp. 4W30, while Nitrosococcus oceanus remained inhibited. None of the other nitrogen sources examined had a significant effect on CO oxidation. No carbon from CO was incorporated into cellular material in the absence of ammonium, even in the presence of alternate nitrogen sources. Cells incubated in the presence of ammonium at concentrations as low as 1.0 mg/L [Formula: see text] N were able to incorporate CO carbon into cellular material. Increasing [Formula: see text] N concentrations to 50 mg/L stimulated the incorporation of CO carbon by Nitrosococcus oceanus. Concentrations of 10 mg/L gave the highest incorporation levels for Nitrosomonas europaea and Nitrosomonas sp. 4W30 and 50 mg/L inhibited the incorporation by these two organisms. The presence of CO inhibited the oxidation of ammonium by all of the organisms tested.