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Journal of Bacteriology, January 2003, p. 302-310, Vol. 185, No. 1
0021-9193/03/$08.00+0     DOI: 10.1128/JB.185.1.302-310.2003
Copyright © 2003, American Society for Microbiology. All Rights Reserved.

A Previously Unrecognized Step in Pentachlorophenol Degradation in Sphingobium chlorophenolicum Is Catalyzed by Tetrachlorobenzoquinone Reductase (PcpD)

MingHua Dai, Julie Bull Rogers, Joseph R. Warner, and Shelley D. Copley*

Department of Molecular, Cellular, and Developmental Biology, and Cooperative Institute for Research in Environmental Sciences, University of Colorado at Boulder, Boulder, Colorado 80309

Received 11 July 2002/ Accepted 29 September 2002

The first step in the pentachlorophenol (PCP) degradation pathway in Sphingobium chlorophenolicum has been believed for more than a decade to be conversion of PCP to tetrachlorohydroquinone. We show here that PCP is actually converted to tetrachlorobenzoquinone, which is subsequently reduced to tetrachlorohydroquinone by PcpD, a protein that had previously been suggested to be a PCP hydroxylase reductase. pcpD is immediately downstream of pcpB, the gene encoding PCP hydroxylase (PCP monooxygenase). Expression of PcpD is induced in the presence of PCP. A mutant strain lacking functional PcpD has an impaired ability to remove PCP from the medium. In contrast, the mutant strain removes tetrachlorophenol from the medium at the same rate as does the wild-type strain. These data suggest that PcpD catalyzes a step necessary for degradation of PCP, but not for degradation of tetrachlorophenol. Based upon the known mechanisms of flavin monooxygenases such as PCP hydroxylase, hydroxylation of PCP should produce tetrachlorobenzoquinone, while hydroxylation of tetrachlorophenol should produce tetrachlorohydroquinone. Thus, we proposed and verified experimentally that PcpD is a tetrachlorobenzoquinone reductase that catalyzes the NADPH-dependent reduction of tetrachlorobenzoquinone to tetrachlorohydroquinone.

* Corresponding author. Mailing address: University of Colorado at Boulder, CIRES, Campus Box 216, Boulder, CO 80309-0216. Phone: (303) 492-6328. Fax: (303) 492-1149. E-mail: copley{at}cires.colorado.edu.

Journal of Bacteriology, January 2003, p. 302-310, Vol. 185, No. 1
0021-9193/03/$08.00+0     DOI: 10.1128/JB.185.1.302-310.2003
Copyright © 2003, American Society for Microbiology. All Rights Reserved.



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