STUDIES ON THE ISOPROPYLBENZENE 2,3-DIOXYGENASE AND THE 3-ISOPROPYLCATECHOL 2,3-DIOXYGENASE GENES ENCODED BY THE LINEAR PLASMID OF RHODOCOCCUS-ERYTHROPOLIS BD2

The enzymes responsible for the degradation of isopropylbenzene (IPB) and cooxidation of trichloroethene (TCE) by Rhodococcus erythropolis B D2 are encoded by the linear plasmid pBD2. Fragments containing IPB ca tabolic genes were cloned from pBD2 and the nucleotide sequence was de termined. By means of database searches and expression of the cloned g enes in recombinant strains, we identified five clustered genes, ipbA1 A2A3A4C, which encode the three components of the IPB 2,3-dioxygenase system, reductase(IPB) (ipbA4), ferredoxin(IPB) (ipbA3) and the two su bunits of the terminal dioxygenase (ipbA1A2), as well as the 3-isoprop ylcatechol (IPC) 2,3-dioxygenase (ipbC). The protein sequences deduced from the ipbA1A2A3A4C gene cluster exhibited significant homology wit h the corresponding proteins of analogous degradative pathways in Cram -negative and Cram-positive bacteria, but the gene order differed from most of them. IPB 2,3-dioxygenase and 3-IPC 2,3-dioxygenase could bot h be expressed in Escherichia coli, but the IPB 2,3-dioxygenase activi ties were too low to be detected by polarographic and TCE degradative means. However, inhibitor studies with the R. erythropolis BD2 wild-ty pe are in accordance with the involvement of the IPB 2,3-dioxygenase i n TCE oxidation.