Summary: Dichloromethane (DCM) dehalogenases enable facultative methylotrophic bacteria to utilize DCM as sole carbon and energy source. DCM-degrading aerobic methylotrophic bacteria expressing a type A DCM dehalogenase were previously shown to share a conserved 4.2 kb HI DNA fragment containing the dehalogenase structural gene, , and , the gene encoding a putative regulatory protein. Sequence analysis of a 10 kb DNA fragment including this region led to the identification of three types of insertion sequences identified as IS , IS and IS, and also two ORFs, and , of unknown function. Two identical copies of element IS flank the conserved 4.2 kb fragment as a direct repeat. The occurrence of these newly identified IS elements was shown to be limited to DCM-utilizing methylotrophs containing a type A DCM dehalogenase. The organization of the corresponding regions in 12 DCM-utilizing strains was examined by hybridization analysis using IS-specific probes. Six different groups could be defined on the basis of the occurrence, position and copy number of IS sequences. All groups shared a conserved 5.6 kb core region with and as well as IS One group of strains including sp. DM1 contained two copies of this conserved core region. The high degree of sequence conservation observed within the genomic region responsible for DCM utilization and the occurrence of clusters of insertion sequences in the vicinity of the genes suggest that a transposon is involved in the horizontal transfer of the DCM-utilization character among methylotrophic bacteria.


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