THE GENUS METHYLOPHAGA, A NEW LINE OF DESCENT WITHIN PHYLOGENETIC BRANCH-GAMMA OF PROTEOBACTERIA

The genus Methylophaga with two species, M. marina and M. thalassica, comprises halophilic methylotrophic bacteria. These organisms utilise C1 compounds through the ribulose monophosphate pathway and are unable to grow on methane. Nearly complete 16S rRNA sequences were obtained for both Methylophaga species by directly sequencing the amplified 16S rRNA gene. These sequences were compared with published 16S rRNA sequences of methylotrophic strains and a large number of marine bacterial strains including several members of the alpha, beta and gamma subclasses of Proteobacteria. Phylogenetic trees were inferred using both parsimony and distance matrix methods. Each topology was analysed by bootstrap. The genus Methylophaga was found to be clearly separated from other methylotrophic bacteria and formed a distinct branch within the gamma subclass of Proteobacteria.