Induction of the halobenzoate catabolic pathway and cometabolism of ortho-chlorobenzoates in Pseudomonas aeruginosa 142 grown on glucose-supplemented media

The aerobic cometabolism of ortho-substitutedchlorobenzoates by Pseudomonas aeruginosa strain 142 growing on glucose-supplemented medium was analyzed. The strain, which can use 2-chlorobenzoate (2-CBA) and 2,4-dichlorobenzoate (2,4-DCBA) as sole carbon and energy sources, showed high rates of 2-CBA metabolism in glucose-fed cells. In contrast, 2,4-DCBA was metabolized only after extended incubation of the full grown culture and depletion of glucose.In addition to the ortho-dehalogenation (ohb ₁₄₂) genes encoding the and subunits of the oxygenase component of a 2-halobenzoate dioxygenase, strain 142 harbours a closely relatedohbABCDFG gene cluster previously identified inP. aeruginosa JB2 (ohb _JB2). The genes for the chlorocatechol ortho-catabolic pathway were identified andsequenced in this strain, showing a near complete identity with the clcABD operon of the pAC27 plasmid. Relative quantification of mRNA by RT-PCR shows apreferential induction of ohb ₁₄₂ by 2-CBA, which is abolished in glucose-grown cultures. The alternate ohb _JB2and clc genes were expressed preferentially in 2,4-DCBAgrown cultures. Only ohb _JB2appears to be expressed in the presence of the carbohydrate. Detection of chlorocatechol-1,2-dioxygenase activity in 2,4-DCBA plus glucose grown cultures suggests the presence of an alternate system for the ortho-cleavage of chlorobenzoates. The recruitment of elements from two halobenzoate dioxygenase systems with different induction patterns, together with achlorocatechol degradative pathway not repressed by carbon catabolite, may allow P. aeruginosa 142 to cometabolize haloaromatics in carbohydrate grown cultures.