Phylogenetic Analysis of Dichloromethane-Utilizing Aerobic Methylotrophic Bacteria

The phylogenetic relationships of 12 aerobic dichloromethane-degrading bacteria that implement different C₁-assimilation pathways was determined based on 16S ribosomal RNA sequences and DNA–DNA hybridization data. The restricted facultative methylotroph Methylophilus leisingerii DM11 with the ribulose monophosphate pathway was found to belong to the genus Methylophilus cluster of the beta subclass of Proteobacteria. The facultative methylotroph Methylorhabdus multivorans DM13 was assigned to a separate branch of the alpha-2 group of Proteobacteria. Paracoccus methylutens DM12, which utilizes C₁-compounds via the Calvin cycle, was found to belong to the alpha-3 group of Proteobacteria (more precisely, to the genus Paracoccus cluster). Thus, phylogenetic analysis confirmed the taxonomic status of these recently characterized bacteria. According to the degree of DNA homology, several novel strains of methylotrophic bacteria were divided into three genotypic groups within the alpha-2 group of the Proteobacteria. Genotypic group 1, comprising strains DM1, DM3, and DM5 through DM9, and genotypic group 3, comprising strain DM10, were phylogenetically close to the methylotrophic bacteria of the genus Methylopila, whereas genotypic group 2 (strain DM4) was close to bacteria of the genus Methylobacterium. The genotypic groups obviously represent distinct taxa of methylotrophic bacteria, whose status should be confirmed by phenotypic analysis.