EVIDENCE THAT PARTICULATE METHANE MONOOXYGENASE AND AMMONIA MONOOXYGENASE MAY BE EVOLUTIONARILY RELATED

Genes encoding particulate methane monooxygenase and ammonia monooxyge nase share high sequence identity. Degenerate oligonucleotide primers were designed, based on regions of shared amino acid sequence between the 27-kDa polypeptides, which are believed to contain the active site s, of particulate methane monooxygenase and ammonia monooxygenase. A 5 25-bp internal DNA fragment of the genes encoding these polypeptides ( pmoA and amoA) from a variety of methanotrophic and nitrifying bacteri a was amplified by PCR, cloned and sequenced. Representatives of each of the phylogenetic groups of both methanotrophs (alpha- and gamma-Pro teobacteria) and ammonia-oxidizing nitrifying bacteria (beta-and gamma -Proteobacteria) were included, Analysis of the predicted amino acid s equences of these genes revealed strong conservation of both primary a nd secondary structure. Nitrosococcus oceanus AmoA showed higher ident ity to PmoA sequences from other members of the gamma-Proteobacteria t han to AmoA sequences. These results suggest that the particulate meth ane monooxygenase and ammonia monooxygenase are evolutionarily related enzymes despite their different physiological roles in these bacteria .