Method for estimating in situ chemo-lithotrophic ammonium oxidation using carbon monoxide oxidation

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A sensitive new method for estimating chemolithotrophic ammonium oxidation (nitrification) has been developed. Carbon monoxide oxidation, using ',CO, is measured with and without the addition of 100 mg I-' of N-Serve, a specific nitrification inhibitor. The N-Serve sensitive CO oxidation can be related to the rate of ammonium oxidation by chemohthotrophic ammonium oxidizers. Methane oxidation, using ',CH,, is also measured to determine the potential for ammonium and CO oxidation by methane oxidizer populations. This method was used to examine pure cultures of ammoniun~ and methane oxidizers, as well as organisms in soil, 2 freshwater lakes, and estuarine waters. Ammonium oxidizers were found to be responsible for 28 to 97 % of the CO oxidation in the environmental samples examined. Ammonium and methane oxidizers were found to have widely different CH, oxidation to CO oxidation ratios, allowing distinction between environmental types where ammonium oxidizers achieve dominance.