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J. Bacteriol. doi:10.1128/JB.01122-07
Copyright (c) 2007, American Society for Microbiology and/or the Listed Authors/Institutions. All Rights Reserved.

The roles of ring-hydroxylating dioxygenases in styrene and benzene catabolism in Rhodococcus jostii RHA1

Department of Microbiology and Immunology, Life Sciences Institute, University of British Columbia, Vancouver, BC, V6T 1Z3, Canada; Department of Bioengineering, Nagaoka University of Technology, Nagaoka, Niigata 940-2188, Japan

^* To whom correspondence should be addressed. Email: leltis{at}interchange.ubc.ca.

	Abstract

Proteomics and targeted gene disruption were used to investigate the catabolism of benzene, styrene, biphenyl and ethylbenzene in Rhodococcus jostii RHA1, a well-studied soil bacterium whose potent polychlorinated biphenyl (PCB)-transforming properties are partly due to the presence of the related Bph and Etb pathways. Of 151 identified proteins, 22 Bph/Etb proteins were among the most abundant in each of biphenyl-, ethylbenzene-, benzene- and styrene-grown cells. Cells grown on biphenyl, ethylbenzene or benzene contained both Bph and Etb enzymes and at least two sets of lower Bph pathway enzymes. By contrast, styrene-grown cells contained no Etb enzymes and only one set of lower Bph pathway enzymes. Gene disruption established that biphenyl dioxygenase (BPDO) was essential for growth of RHA1 on benzene or styrene, but that ethylbenzene dioxygenase (EBDO) was not required for growth on any of the tested substrates. Moreover, whole cell assays of the bphAa and etbAa1::cmrA etbAa2::aphII mutants demonstrated that while both dioxygenases preferentially transformed biphenyl, only BPDO transformed styrene. Deletion of pcaL of the -ketoadipate pathway disrupted growth on benzene, but not other substrates. Thus, styrene and benzene are degraded via meta- and ortho-cleavage, respectively. Finally, catalases were more abundant during growth on non-polar aromatic compounds than on aromatic acids. This suggests that the relaxed specificity of BPDO and EBDO that enable RHA1 to grow on a range of compounds comes at the cost of increased uncoupling during the latter's initial transformation. The stress response may augment RHA1's ability to degrade PCBs and other pollutants that induce similar uncoupling.