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Novel insights into the interplay between peripheral reactions encoded by xyl genes and the chlorocatechol pathway encoded by tfd genes for the degradation of chlorobenzoates by Ralstonia eutropha JMP134

Laboratorio de Microbiología, Departamento de Genética Molecular y Microbiología, Facultad de Ciencias Biológicas, Pontificia Universidad Católica de Chile, Casilla 114-D Santiago, Chile¹
Division of Microbiology, National Research Centre for Biotechnology – GBF, Braunschweig, Germany²

Author for correspondence: Bernardo González. Tel: +56 2 6862845. Fax: +56 2 2225515. e-mail: bgonzale{at}genes.bio.puc.cl

Many bacteria can grow on chloroaromatic pollutants because they can transform them into chlorocatechols, which are further degraded by enzymes of a specialized ortho-cleavage pathway. Ralstonia eutropha JMP134 is able to grow on 3-chlorobenzoate by using two pJP4-encoded, ortho-cleavage chlorocatechol degradation gene clusters (tfdC_ID_IE_IF_I and tfdD_IIC_IIE_IIF_II). Very little is known about the acquisition of new catabolic genes encoding enzymes that lead to the formation of chlorocatechols in R. eutropha JMP134. The effect on the catabolic properties of an R. eutropha JMP134 derivative that received the xylS–xylXYZL gene module, encoding the xylS-regulated expression of the broad-substrate-range toluate 1,2-dioxygenase (xylXYZ) and the 1,2-dihydro-1,2-dihydroxytoluate dehydrogenase (xylL) from pWW0, which allows the transformation of 4-chlorobenzoate into 4-chlorocatechol, was studied. Such a derivative could efficiently grow on 4-chlorobenzoate. Unexpectedly, this derivative also grew on 3,5-dichlorobenzoate, a substrate for XylXYZL but not an inducer of the XylS regulatory protein. The ability to grow on 4-chlorobenzoate or 3,5-dichlorobenzoate was also observed in derivatives of strain JMP134 containing the xyl gene module but lacking xylS, indicating the presence of an xylS-like element in R. eutropha with an inducer profile different from that of the pWW0-encoded regulator. Growth on 4-chlorobenzoate was also observed after introduction of the xyl gene module into strain JMP222, a JMP134 derivative lacking pJP4, but only if multiple copies of tfdC_ID_IE_IF_I or tfdD_IIC_IIE_IIF_II were present. However, only the derivative containing multiple copies of tfdD_IIC_IIE_IIF_II was able to grow on 3,5-dichlorobenzoate. These observations indicate that although the acquisition of new catabolic genes actually enhances the catabolic abilities of R. eutropha JMP134, these new properties are strongly influenced by the dosage of the tfd genes, the presence of a chromosomal xylS-like regulatory element and the different contributions of the tfd gene clusters.

Keywords: chloroaromatic compounds, maleylacetate reductase, gene acquisition, AraC/XylS regulatory family, gene dosage

Abbreviations: CB, chlorobenzoate; 3-CB, 3-chlorobenzoate; 4-CB, 4-chlorobenzoate; 3,5-DCB, 3,5-dichlorobenzoate; 3-MB, 3-methylbenzoate; 4-MB, 4-methylbenzoate; 2,4-D, 2,4-dichlorophenoxyacetate

This article has been cited by other articles:

				D. Perez-Pantoja, T. Ledger, D. H. Pieper, and B. Gonzalez Efficient Turnover of Chlorocatechols Is Essential for Growth of Ralstonia eutropha JMP134(pJP4) in 3-Chlorobenzoic Acid J. Bacteriol., March 1, 2003; 185(5): 1534 - 1542. [Abstract] [Full Text] [PDF]