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

The aerobic cometabolism of ortho-substituted chlorobenzoates by Pseudomona s aeruginosa strain 142 growing on glucose-supplemented medium was analyzed . The strain, which can use 2-chlorobenzoate (2-CBA) and 2,4-dichlorobenzoa te (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 onl y after extended incubation of the full grown culture and depletion of gluc ose. In addition to the ortho-dehalogenation (ohb(142)) genes encoding the alpha and beta subunits of the oxygenase component of a 2-halobenzoate diox ygenase, strain 142 harbours a closely related ohbABCDFG gene cluster previ ously identified in P. aeruginosa JB2 (ohb(JB2)). The genes for the chloroc atechol ortho-catabolic pathway were identified and sequenced in this strai n, showing a near complete identity with the clcABD operon of the pAC27 pla smid. Relative quantification of mRNA by RT-PCR shows a preferential induct ion of ohb(142) by 2-CBA, which is abolished in glucose-grown cultures. The alternate ohb(JB2) and clc genes were expressed preferentially in 2,4-DCBA grown cultures. Only ohb(JB2) appears to be expressed in the presence of t he carbohydrate. Detection of chlorocatechol-1,2-dioxygenase activity in 2, 4-DCBA plus glucose grown cultures suggests the presence of an alternate sy stem for the ortho-cleavage of chlorobenzoates. The recruitment of elements from two halobenzoate dioxygenase systems with different induction pattern s, together with a chlorocatechol degradative pathway not repressed by carb on catabolite, may allow P. aeruginosa 142 to cometabolize haloaromatics in carbohydrate grown cultures.