The amo operon in marine, ammonia-oxidizing gamma-proteobacteria

While there is an extensive database of genes encoding ammonia monooxygenas e (amo) found in the ammonia-oxidizing beta-proteobacteria, few amo sequenc es are available representing the gamma-proteobacteria. We sequenced the co mplete amo operon (amoCAB) for Nitrosococcus oceani (ATCC 19707), a marine, autotrophic, ammonia-oxidizing bacterium belonging to the gamma-subdivisio n of the proteobacteria. An additional autotrophic, ammonia-oxidizing bacte rium isolated from a marine environment (strain C-113) was identified as be longing to the Nitrosococcus genus by 16S rDNA analysis and its amo operon was sequenced. This is the first report of a full-length sequence for the a mo operon from a gamma-subdivision autotrophic ammonia-oxidizing bacterium. The N. oceani and C-113 amo genes were 88-90% identical to each other, 49- 53% identical to the pmo genes encoding the related particulate methane mon ooxygenase of Methylococcus capsulatus (Bath), and 39-42% identical to the amo genes of the P-subdivision autotrophic ammonia-oxidizing bacteria. In b oth Nitrosococcus strains, the amo operon was found as a single copy and co ntained three genes, amoC, amoA, amoB, with intergenic spacer regions betwe en amoC and amoA (286 bp) and between amoA and amoB (65 bp). We conclude th at the amo genes will allow for a finer scale phylogenetic differentiation than 16S rDNA within the gamma-subdivision AOB. (C) 1999 Federation of:Euro pean Microbiological Societies. Published by Elsevier Science B.V. All righ ts reserved.