Phylogenetic analysis of trichloroethylene-degrading bacteria newly isolated from soil polluted with this contaminant

Five methanotrophs (strains 18-2, EB1, KSWIII, KSPIII and KSPIII) and three aromatic compound oxidizers (strains KP22, KP24 and KT1) were isolated from the natural field polluted with trichloroethylene (TCE). Phylogenetic analysis based on 16S rRNA gene sequence suggested that all of the isolates belonged to the class Proteobacteria. Two of the methanotrophic isolates, strains 18-2 and EB1, were closely related to Methylocystis sp. strain M in the α subclass of Proteobacteria with sequence similarities of 98.2–98.4%, while strains KSWIII, KSPIII and KSPII were akin to Methylomonas methanica in the γ subclass of Proteobacteria with sequence similarities of 97.8–98.1%. The aromatic compounds oxidizers, strains KP22, KP24 and KT1, were assigned to the β subclass of Proteobacteria, and classified as Bordetella sp. (97.2–97.8% sequence similarity to species of the genus Bordetella), Burkholderia cepacia (99.2%) and Ralstonia eutropha (99.4%), respectively. All isolates degraded TCE when cells were grown with the appropriate substrate, i.e., methane, phenol or toluene. Detailed kinetic analyses of their TCE degradation revealed that the rates of degradation (k1) among the isolates were 10–36 ml of TCE/mg of dry cell weight/h, and the transformation capacities (Tc) were 0.01–0.13 mg of TCE/mg of dry cell weight.