RESUMO
While there is an extensive database of genes encoding ammonia monooxygenase (amo) found in the ammonia-oxidizing beta-proteobacteria, few amo sequences are available representing the gamma-proteobacteria. We sequenced the complete amo operon (amoCAB) for Nitrosococcus oceani (ATCC 19707), a marine, autotrophic, ammonia-oxidizing bacterium belonging to the gamma-subdivision of the proteobacteria. An additional autotrophic, ammonia-oxidizing bacterium isolated from a marine environment (strain C-113) was identified as belonging 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 amo 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 monooxygenase of Methylococcus capsulatus (Bath), and 39-42% identical to the amo genes of the beta-subdivision autotrophic ammonia-oxidizing bacteria. In both Nitrosococcus strains, the amo operon was found as a single copy and contained three genes, amoC, amoA, amoB, with intergenic spacer regions between amoC and amoA (286 bp) and between amoA and amoB (65 bp). We conclude that the amo genes will allow for a finer scale phylogenetic differentiation than 16S rDNA within the gamma-subdivision AOB.
Assuntos
Bradyrhizobiaceae/genética , Óperon/genética , Oxirredutases/genética , Microbiologia da Água , Sequência de Aminoácidos , Amônia/metabolismo , Sequência de Bases , Southern Blotting , Bradyrhizobiaceae/metabolismo , DNA Ribossômico/genética , Genes Bacterianos , Dados de Sequência Molecular , Reação em Cadeia da Polimerase , RNA Ribossômico 16S/análise , Água do MarRESUMO
Nitrifying bacteria such as Nitrosomonas europaea and Nitrosospira sp. NpAV use ammonia monooxygenase (AMO) for oxidation of their primary growth substrate, ammonia. Two polypeptides of AMO are coded for by contiguous genes, amoA and amoB, which are preceded by a third gene, amoC. The amoCAB clusters are present in multiple copies in nitrifying bacteria of the beta subdivision. These bacteria also have one amoC copy that is not adjacent to a copy of amoAB. The seven known amoC genes in different nitrifiers code for similar polypeptides (> 68%). Reverse transcriptase-polymerase chain reactions and Northern blots indicated that amoC from the amoCAB cluster is contained on a transcript with amoAB. Two other transcripts were detected with amo probes and may be a product of processing of the amoCAB mRNA or independent transcripts.