Formation of chlorocatechol meta cleavage products by a pseudomonad during metabolism of monochlorobiphenyls

Abstract

Pseudomonas cepacia P166 was able to metabolize all monochlorobiphenyls to the respective chlorobenzoates. Although they transiently accumulated, the chlorobenzoate degradation intermediates were further metabolized to chlorocatechols, which in turn were meta cleaved. 2- and 3-Chlorobiphenyl both produced 3-chlorocatechol, which was transformed to an acyl halide upon meta cleavage. 3-Chlorocatechol metabolism was toxic to the cells and impeded monochlorobiphenyl metabolism. In the case of 2-chlorobiphenyl, toxicity was manifested as a diminished growth rate, which nevertheless effected rapid substrate utilization. In the case of 3-chlorobiphenyl, which generates 3-chlorocatechol more rapidly than does 2-chlorobiphenyl, toxicity was manifested as a decrease in viable cells during substrate utilization. 4-Chlorobenzoate was transformed to 4-chlorocatechol, which was metabolized by a meta cleavage pathway leading to dehalogenation. Chloride release from 4-chlorocatechol metabolism, however, was slow and did not coincide with rapid 4-chlorocatechol turnover. Growth experiments with strain P166 on monochlorobiphenyls illustrated the difficulties of working with hydrophobic substrates that generate toxic intermediates. Turbidity could not be used to measure the growth of bacteria utilizing monochlorobiphenyls because high turbidities were routinely measured from cultures with very low viable-cell counts.