Genes for the subunits of particulate methane monooxygenase, PmoABC, have been sequenced from the γ-proteobacterial methanotroph Bath. Bath contains two complete copies of as well as a third copy of The two regions were almost identical at the nucleotide sequence level, differing in only 13 positions in 3183 bp. At the amino acid level, each translated gene product contained only one differing residue in each copy. However, the sequence was more divergent from the two other copies at both the far N-terminus and far C-terminus. Chromosomal insertion mutations were generated in all seven genes. Null mutants could not be obtained for suggesting that it may play an essential role in growth on methane. Null mutants were obtained for and All of these mutants grew on methane, demonstrating that both gene copies were functional. Copy 1 mutants showed about two-thirds of the wild-type whole-cell methane oxidation rate, while copy 2 mutants showed only about one-third of the wild-type rate, indicating that both gene copies were necessary for wild-type particulate methane monooxygenase activity. It was not possible to obtain double null mutants that were defective in both copies, which may indicate that some expression of pMMO is important for growth.


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