Carbon monoxide oxidation by chemolithotrophic ammonium oxidizers

Chemolithotrophic nitrifying bacteria were examined with respect to their ability to oxidize carbon monoxide in the presence and absence of ammonium. All of the ammonium oxidizers tested, including Nitrosomonas europaea and Nitrosococcus oceanus, were able to oxidize CO to CO 2 in the presence and absence of ammonium. None of the organisms tested incorporated any of the carbon from CO into cellular components in the absence of ammonium. All were able to oxidize CO at trace concentrations of <0.5 nM. None of the nitrite oxidizers examined were capable of CO oxidation. CO oxidation by Nitrosomonas europaea, Nitrosococcus oceanus, and Nitrosomonas sp. 4S30, a marine ammonium oxidizer, were examined with respect to CO concentration and time course of CO oxidation, both in the presence and absence of 10 mg/L NH 4 N. The CO oxidation rates at a CO concentration of 300 nL/L in the absence of ammonium ranged from 0.048 nmol/h per 10 6 cells for Nitrosomonas sp. 4W30 to 0.0025 nmol/h per 10 6 cells for N. europaea.