Regulation of catabolic pathways of phenoxyacetic acids and phenols in Alcaligenes eutrophus JMP 134

Abstract

Alicaligenes eutrophus JMP 134 is able to grow on 2,4-dichloro-, 4-chloro-2-methyl- and 2-methylphenoxy acetic acid. The unsubstituted phenoxyacetic acid, however, is no growth substrate due to very poor induction of the 2,4-D monooxygenase. Spontaneous mutants of Alcaligenes eutrophus JMP 134 capable of growth with phenoxyacetic acid were selected on agar plates. One of these mutants, designated Alcaligenes eutrophus JMP 134-1, shows constitutive production of six enzymes of the 2,4-D pathway, which were known to be localized in at least three different transcriptional units. A common regulatory gene is postulated to be mutated. 2,4-Dichloro-, 4-chloro-2-methyl- and 2-methylphenoxyacetic acid were the inducers of the enzymes of the ldquochloroaromatic pathwayrdquo in Alcaligenes eutrophus JMP 134. Phenol and 2-methylphenol, metabolites of the degradation of phenoxyacetic acid and 2-methylphenoxyacetic acid, were shown to be inducers of the meta-cleavage pathway, whereas 2,4-dichlorophenol and 4-chloro-2-methylphenol were not. Thus efficient regulation prevents chloroaromatics from being misrouted into the unproductive meta-cleavage pathway. Because 2,4-dichloro-and 4-chloro-2-methylphenol did not show any induction potential, they were growth substrates only for the mutant strain JMP 134-1.