Chlorophenol hydroxylases encoded by plasmid pJP4 differentially contribute to chlorophenoxy acetic acid degradation

Ledger, T.; Pieper DH; Gonzalez, B.

Abstract

Phenoxyalkanoic compounds are used worldwide as herbicides. Cupriavidus necator JMP134(pJP4) catabolizes 2,4-dichlorophenoxyacetate (2,4-D) and 4-chloro-2-methylphenoxyacetate (MCPA), using tfd functions carried on plasmid pJP4. TfdA cleaves the ether bonds of these herbicides to produce 2,4-dichlorophenol (2,4-DCP) and 4-chloro-2-methylphenol (MCP), respectively. These intermediates can be degraded by two chlorophenol hydroxylases encoded by the tfdBI and tfdBII genes to produce the respective chlorocatechols. We studied the specific contribution of each of the TfdB enzymes to the 2,4-D/MCPA degradation pathway. To accomplish this, the tfdB I and tfdBII genes were independently inactivated, and growth on each chlorophenoxyacetate and total chlorophenol hydroxylase activity were measured for the mutant strains. The phenotype of these mutants shows that both TfdB enzymes are used for growth on 2,4-D or MCPA but that TfdB, contributes to a significantly higher extent than TfdBII. Both enzymes showed similar specificity profiles, with 2,4-DCP, MCP, and 4-chlorophenol being the best substrates. An accumulation of chlorophenol was found to inhibit chlorophenoxyacetate degradation, and inactivation of the tfdB genes enhanced the toxic effect of 2,4-DCP on C. necator cells. Furthermore, increased chlorophenol production by overexpression of TfdA also had a negative effect on 2,4-D degradation by C. necator JMP134 and by a different host, Burkholderia xenovorans LB400, harboring plasmid pJP4. The results of this work indicate that codification and expression of the two tfdB genes in pJP4 are important to avoid toxic accumulations of chlorophenols during phenoxyacetic acid degradation and that a balance between chlorophenol-producing and chlorophenol-consuming reactions is necessary for growth on these compounds. Copyright © 2006, American Society for Microbiology. All Rights Reserved.

Más información

Título según WOS: Chlorophenol hydroxylases encoded by plasmid pJP4 differentially contribute to chlorophenoxy acetic acid degradation
Título según SCOPUS: Chlorophenol hydroxylases encoded by plasmid pJP4 differentially contribute to chlorophenoxyacetic acid degradation
Título de la Revista: APPLIED AND ENVIRONMENTAL MICROBIOLOGY
Volumen: 72
Número: 4
Editorial: AMER SOC MICROBIOLOGY
Fecha de publicación: 2006
Página de inicio: 2783
Página final: 2792
Idioma: English
URL: http://aem.asm.org/cgi/doi/10.1128/AEM.72.4.2783-2792.2006
DOI:

10.1128/AEM.72.4.2783-2792.2006

Notas: ISI, SCOPUS