title: Biological degradation of 4-chlorobenzoic acid by a PCB-metabolizing bacterium through a pathway not involving (chloro)catechol.
abstract: Cupriavidus sp. strain SK-3, previously isolated on polychlorinated biphenyl mixtures, was found to aerobically utilize a wide spectrum of substituted aromatic compounds including 4-fluoro-, 4-chloro- and 4-bromobenzoic acids as a sole carbon and energy source. Other chlorobenzoic acid (CBA) congeners such as 2-, 3-, 2,3-, 2,5-, 3,4- and 3,5-CBA were all rapidly transformed to respective chlorocatechols (CCs). Under aerobic conditions, strain SK-3 grew readily on 4-CBA to a maximum concentration of 5 mM above which growth became impaired and yielded no biomass. Growth lagged significantly at concentrations above 3 mM, however chloride elimination was stoichiometric and generally mirrored growth and substrate consumption in all incubations. Experiments with resting cells, cell-free extracts and analysis of metabolite pools suggest that 4-CBA was metabolized in a reaction exclusively involving an initial hydrolytic dehalogenation yielding 4-hydroxybenzoic acid, which was then hydroxylated to protocatechuic acid (PCA) and subsequently metabolized via the β-ketoadipate pathway. When strain SK-3 was grown on 4-CBA, there was gratuitous induction of the catechol-1,2-dioxygenase and gentisate-1,2-dioxygenase pathways, even if both were not involved in the metabolism of the acid. While activities of the modified ortho- and meta-cleavage pathways were not detectable in all extracts, activity of PCA-3,4-dioxygenase was over ten-times higher than those of catechol-1,2- and gentisate-1,2-dioxygenases. Therefore, the only reason other congeners were not utilized for growth was the accumulation of CCs, suggesting a narrow spectrum of the activity of enzymes downstream of benzoate-1,2-dioxygenase, which exhibited affinity for a number of substituted analogs, and that the metabolic bottlenecks are either CCs or catabolites of the modified ortho-cleavage metabolic route.
authors.affiliation: Department of Microbiology, Faculty of Science, University of Lagos, Akoka, Yaba, Lagos, Nigeria. sadebusoye@yahoo.com.|Chemische Mikrobiologie, Bergische Universität-Gesamthochschule Wuppertal, Wuppertal, Germany. sadebusoye@yahoo.com.
authors.forename: Sunday A
authors.initials: SA
authors.lastname: Adebusoye
mesh_terms: D001673:Biodegradation, Environmental; D002396:Catechols / Q000378:metabolism*; D002723:Chlorobenzoates / Q000378:metabolism*; D049921:Cupriavidus / Q000378:metabolism*; D049308:Dioxygenases / Q000378:metabolism; D062385:Hydroxybenzoates / Q000378:metabolism; D010101:Oxygen Consumption; D011078:Polychlorinated Biphenyls / Q000378:metabolism*
chemical_list: D002396:Catechols; D002723:Chlorobenzoates; D062385:Hydroxybenzoates; C009091:protocatechuic acid; D011078:Polychlorinated Biphenyls; D049308:Dioxygenases; C040768:4-chlorobenzoic acid
keywords: Biodegradation; Chlorobenzoic acid; Chlorocatechol; Hydrolytic dehalogenation; Protocatehuate-3,4-dioxygenase