Molecular diversity of plasmids bearing genes that encode toluene and xylene metabolism in Pseudomonas strains isolated from different contaminated sites in Belarus

Twenty different Pseudomonas strains utilizing m-toluate were isolated from oil-contaminated soil samples near Minsk, Belarus. Seventeen of these isol ates carried plasmids ranging in size from 78 to about 200 kb (assigned pSV S plasmids) and encoding the meta cleavage pathway for toluene metabolism. Most plasmids were conjugative but of unknown incompatibility groups, excep t for one, which belonged to the IncP9 group. The organization of the genes for toluene catabolism was determined by restriction analysis and hybridiz ation with xyl gene probes of pWW0. The majority of the plasmids carried xy l-type genes highly homologous to those of pWW53 and organized in a similar manner (M. T. Gallegos, P. A. Williams, and J. L. Ramos, J. Bacteriol. 179 :5024-5029, 1997), with two distinguishable meta pathway operons, one upper pathway operon, and three xylS-homologous regions. All of these plasmids a lso possessed large areas of homologous DNA outside the catabolic genes, su ggesting a common ancestry. Two other pSVS plasmids carried only one meta p athway operon, one upper pathway operon, and one copy each of xylS and xylR . The backbones of these two plasmids differed greatly from those of the ot hers. Whereas these parts of the plasmids, carrying the xyl genes, were mos tly conserved between plasmids of each group, the noncatabolic parts had un dergone intensive DNA rearrangements. DNA sequencing of specific regions ne ar and within the xylTE and xyl4 genes of the pSVS plasmids confirmed the s trong homologies to the xyl genes of pWW53 and pWWO. However, several recom binations were discovered within the upper pathway operons of the pSVS plas mids and pWWO. The main genetic mechanisms which are thought to have result ed in the present-day configuration of the xyl operons are discussed in lig ht of the diversity analysis carried out on the pSVS plasmids.