ASSOCIATION OF NEWLY DISCOVERED IS-ELEMENTS WITH THE DICHLOROMETHANE UTILIZATION GENES OF METHYLOTROPHIC BACTERIA

Dichloromethane (DCM) dehalogenases enable facultative methylotrophic bacteria to utilize DCM as sole carbon and energy source. DCM-degradin g aerobic methylotrophic bacteria expressing a type A DCM dehalogenase were previously shown to share a conserved 4.2 kb BamHI DNA fragment containing the dehalogenase structural gene, dcmA, and dcmR, the gene encoding a putative regulatory protein. Sequence analysis of a 10 kb D NA fragment including this region led to the identification of three t ypes of insertion sequences identified as IS1354, IS1355 and IS1357. a nd also two ORFs, orf353 and orf192, of unknown function. Two identica l copies of element IS1354 flank the conserved 4.2 kb fragment as a di rect 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 dcm regions i n 12 DCM-utilizing strains was examined by hybridization analysis usin g IS-specific probes. Six different groups could be defined on the bas is of the occurrence, position and copy number of IS sequences. All gr oups shared a conserved 5.6 kb core region with dcmA, dcmR, orf353 and orf192 as well as IS1357. One group of strains including Pseudomonas sp. DM1 contained two copies of this conserved core region. The high d egree of sequence conservation observed within the genomic region resp onsible for DCM utilization and the occurrence of clusters of insertio n sequences in the vicinity of the dent genes suggest that a transposo n is involved in the horizontal transfer of the DCM-utilization charac ter among methylotrophic bacteria.