Ammonia-oxidizing bacteria carry out the first step of nitrification, producing nitrite that is subsequently converted to nitrate, which may contribute to environmental pollution. The objective of this study was to gain insight into the functional diversity of ammonia-oxidizing bacteria in agricultural soils. We investigated the urease encoding gene sequences of several nitrifying bacteria and the kinetics of nitrification of soils treated with different nitrogen sources. Many, but not all, ammonia-oxidizing bacteria produce urease and are capable of hydrolyzing urea for their source of ammonium. The urease operons were sequenced from the betaproteobacterial Nitrosospira sp. NpAV and the gammaproteobacterial Nitrosococcus oceani. In both organisms, all seven ure genes were contiguous: ureDABCEFG. Southern analyses revealed two copies of ureC in Nitrosospira sp. NpAV and one copy in the N. oceani genome. Several regions were suitable primer targets for obtaining further ureC sequences from additional ammonia-oxidizing bacteria. (Abstract shortened by UMI.)
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