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Journal of Bacteriology, July 2002, p. 3492-3500, Vol. 184, No. 13
0021-9193/02/$04.00+0 DOI: 10.1128/JB.184.13.3492-3500.2002
Copyright © 2002, American Society for Microbiology. All Rights Reserved.
Genetic and Biochemical Characterization of a 2,4,6-Trichlorophenol Degradation Pathway in Ralstonia eutropha JMP134
Tai Man Louie, Christopher M. Webster, and Luying Xun*
School of Molecular Biosciences, Washington State University, Pullman, Washington 99164-4234
Received 28 December 2001/
Accepted 12 April 2002
Ralstonia eutropha JMP134 can grow on several chlorinated aromatic pollutants, including 2,4-dichlorophenoxyacetate and 2,4,6-trichlorophenol (2,4,6-TCP). Although a 2,4,6-TCP degradation pathway in JMP134 has been proposed, the enzymes and genes responsible for 2,4,6-TCP degradation have not been characterized. In this study, we found that 2,4,6-TCP degradation by JMP134 was inducible by 2,4,6-TCP and subject to catabolic repression by glutamate. We detected 2,4,6-TCP-degrading activities in JMP134 cell extracts. Our partial purification and initial characterization of the enzyme indicated that a reduced flavin adenine dinucleotide (FADH2)-utilizing monooxygenase converted 2,4,6-TCP to 6-chlorohydroxyquinol (6-CHQ). The finding directed us to PCR amplify a 3.2-kb fragment containing a gene cluster (tcpABC) from JMP134 by using primers designed from conserved regions of FADH2-utilizing monooxygenases and hydroxyquinol 1,2-dioxygenases. Sequence analysis indicated that tcpA, tcpB, and tcpC encoded an FADH2-utilizing monooxygenase, a probable flavin reductase, and a 6-CHQ 1,2-dioxygenase, respectively. The three genes were individually inactivated in JMP134. The tcpA mutant failed to degrade 2,4,6-TCP, while both tcpB and tcpC mutants degraded 2,4,6-TCP to an oxidized product of 6-CHQ. Insertional inactivation of tcpB may have led to a polar effect on downstream tcpC, and this probably resulted in the accumulation of the oxidized form of 6-CHQ. For further characterization, TcpA was produced, purified, and shown to transform 2,4,6-TCP to 6-CHQ when FADH2 was supplied by an Escherichia coli flavin reductase. TcpC produced in E. coli oxidized 6-CHQ to 2-chloromaleylacetate. Thus, our data suggest that JMP134 transforms 2,4,6-TCP to 2-chloromaleylacetate by TcpA and TcpC. Sequence analysis suggests that tcpB may function as an FAD reductase, but experimental data did not support this hypothesis. The function of TcpB remains unknown.
* Corresponding author. Mailing address: School of Molecular Biosciences, Science Hall 301, Washington State University, Pullman, WA 99164-4234. Phone: (509) 335-2787. Fax: (509) 335-1907. E-mail:
xun{at}mail.wsu.edu
Journal of Bacteriology, July 2002, p. 3492-3500, Vol. 184, No. 13
0021-9193/02/$04.00+0 DOI: 10.1128/JB.184.13.3492-3500.2002
Copyright © 2002, American Society for Microbiology. All Rights Reserved.
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