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

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Abstract
A sensitive new method for estimating [bacterial] chemolithotrophic ammonium oxidation (nitrification) was developed. CO oxidation, using 14CO, is measured with and without addition of 100 mg l-1 of N-Serve, a specific nitrification inhibitor. The N-Serve sensitive CO oxidation can be related to the rate of ammonium oxidation by chemolithotrophic ammonium oxidizers. Methane oxidation, using 14CH4 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 ammonium and methane oxidizers and organisms in soil, 2 freshwater lakes and estuarine waters. Ammonium oxidizers were responsible for 28-97% of the CO oxidation in the environmental samples examined. Ammonium and methane oxidizers have widely different CH4 oxidation to CO oxidation ratios, allowing distinction between environmental types where ammonium oxidizers achieve dominance.