Effects of various parameters on carbon monoxide oxidation by ammonium oxidizers

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Abstract
The effects of temperature, pH, N source, cell concentration and the interactions between ammonium and CO were examined with respect to the oxidation of CO 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 NH4+ N initially inhibited CO oxidation in all 3 organisms; after 48 h, the presence of ammonium stimulated the CO-oxidizing ability of N. europaea and Nitrosomonas sp. 4W30, while N. oceanus remained inhibited. None of the other N sources examined had a significant effect on CO oxidation. No C from CO was incorporated into cellular material in the absence of ammonium, even in the presence of alternate N sources. Cells incubated in the presence of ammonium at concentrations as low as 1.0 mg/l NH4+ N were able to incorporate CO C into cellular material. Increasing NH4+ N concentrations to 50 mg/l stimulated the incorporation of CO C by N. oceanus. Concentrations of 10 mg/l gave the highest incorporation levels for N. europaea and Nitrosomonas sp. 4W30 and 50 mg/l inhibited the incorporation by these 2 organisms. The presence of CO inhibited the oxidation of ammonium by all of the organisms tested.