Affiliation:
1. Laboratorio de Microbiología, Departamento de Genética Molecular y Microbiología, Millennium Nucleus on Microbial Ecology and Environmental Microbiology and Biotechnology, Facultad de Ciencias Biológicas, Pontificia Universidad Católica de Chile, Santiago, Chile
2. Biodegradation Laboratory, Division of Microbiology, GBF, Braunschweig, Germany
Abstract
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
tfdB
I
and
tfdB
II
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
tfdB
II
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
I
contributes to a significantly higher extent than TfdB
II
. 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.
Publisher
American Society for Microbiology
Subject
Ecology,Applied Microbiology and Biotechnology,Food Science,Biotechnology
Cited by
48 articles.
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