Alkylbenzene Degradation and Cooxidation of Trichloroethene by Rhodococcus erythropolis BD2 is Encoded on pBD2

The complete sequence of the linear conjugative 210,205-bp plasmid pBD2, which confers to R. erythropolis strain BD2 the ability to oxidize isopropyl-benzene and to cometabolize trichloroethene (Dabrock et al. 1994; Kesseler et al. 1996), has been reported (Stecker et al. 2003). Plasmid pBD2 additionally mediates arsenite and mercury resistance (Dabrock et al. 1994). The gene organization on pBD2 and the high number of transposon-related hy pothetical genes suggest a modular composition of the plasmid that presumably arose from horizontal gene transfer events and dynamic rearrangements. The ipb genes coding for the components of isopropylbenzene 2,3-dioxygenase (ipbA), cz's-dihydrodiol dehydrogenase (IpbB), and the meta ring cleavage enzyme 3-isopropylcatechol 2,3-dioxygenase (IpbC), and adjacent genes of a two-component signal transduction system (IpbST), are flanked by putative transposase genes and preceded by an IS element. Figure 5 indicates that apart from an insertion between ipbT and alkK (pBD2.164), the gene organization of the ipb locus of pBD2 is very similar to that of the corresponding bph locus on pRHL1 of Rhodococcus sp. RHA1. Moreover, isopropyl 2,3-dioxygenase and 3-isopropylcatechol 2,3-dioxygenase exhibit 94-100% identity to the gene products of the bphA and bphCl genes located on pRHL1 (Shimizu et al. 2001; Stecker et al. 2003). The putative genes pBD2.165 and pBD2.164 (alkK) on pBD2, presumed to encode an enoyl-CoA hydratase and a medium-chain acyl-CoA ligase, show 98 and 99% identity to ro08049 and ro08050 of pRHL1, respectively. A gene designated ipbD, presumed to code for 2-hydroxy-6-oxohepta-2,4-dienoate hydrolase, is located 10 kb downstream of the other ipb genes; this gene is also flanked by putative transposase genes and IS sequences. Its deduced product is identical to the EtbD1 protein encoded on pRHL1 of strain RHA1 (Stecker et al. 2003).

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