Pathways of 3-Chlorobenzoate Degradation by Rhodococcus opacus strains 1CP and 6a

Abstract

3-Chlorobenzoic acid (3-CBA) is widely used as a precursor/preservative in industry and agriculture and is therefore a known environmental contaminant. The key stages of 3-CBA decomposition by Rhodococcus opacus strains 1CP and 6a were studied. Comparative characterization of the substrate specificity of 3-chlorobenzoate 1,2-dioxygenase (3-CBA 1,2-DO), induced in the strains grown in the presence of 3‑CBA, was carried out. These enzymes were established to have a wider substrate specificity than the benzoate 1,2-dioxygenase (1,2-BDO) of R. opacus strain 1CP, which is induced during growth of R. opacus strain 1CP in the presence of benzoate. Benzoate, 3-CBA, and 3,4-dihydroxybenzoate served as substrates for 3‑CBA 1,2-DO. During the degradation of 3-CBA by R. opacus 1CP cells, both 3-chloro- and 4-chlorocatechol (3-CCat and 4-CCat) were detected. R. opacus 6a efficiently degraded 3-CBA without accumulation of intermediates. The difference in the pathways of 3-CBA degradation by these strains was shown: via the pathway of ortho-cleavage of 3-chlorocatechol in R. opacus 1CP and of 4-chlorocatechol in R. opacus 6a. In the genome of the strain R. opacus 6a, the genes encoding chlorocatechol 1,2-dioxygenase and chloromuconate cycloisomerase were found, which were 98-99% identical to the genes of R. opacus 1CP encoding 4‑chlorocatechol 1,2-dioxygenase (4-CCat 1,2-DO) and 3-chloromuconate cycloisomerase (3-CMCI) of the modified ortho-cleavage pathway for conversion of 4-chlorocatechol (the intermediate of 4-chlorophenol degradation). It was shown for the strains under study that implementation of different pathways for 3-CBA decomposition was predestined not by the metabolic capabilities of bacteria, but by the substrate specificity of 3-CBA 1,2-DO, the enzyme that initiates 3-CBA degradation.