Metabolism of Chlorotoluenes by Burkholderia sp. Strain PS12 and Toluene Dioxygenase of Pseudomonas putida F1: Evidence for Monooxygenation by Toluene and Chlorobenzene Dioxygenases

Abstract

The degradation of toluene by Pseudomonas putida F1 and of chlorobenzenes by Burkholderia sp. strain PS12 is initiated by incorporation of dioxygen into the aromatic nucleus to form cis-dihydrodihydroxybenzenes. Toluene-grown cells of P. putida F1 and 3-chlorobenzoate-grown cells of Burkholderia sp. strain PS12 were found to monooxygenate the side chain of 2- and 3-chlorotoluene to the corresponding chlorobenzyl alcohols. Further metabolism of these products was slow, and the corresponding chlorobenzoates were usually observed as end products, whereas the 3-chlorobenzoate produced from 3-chlorotoluene in Burkholderia sp. strain PS12 was metabolized further. Escherichia coli cells containing the toluene dioxygenase genes from P. putida F1 oxidized 2- and 3-chlorotoluene to the corresponding chlorobenzyl alcohols as major products, demonstrating that this enzyme is responsible for the observed side chain monooxygenation. Two methyl- and chloro-substituted 1,2-dihydroxycyclohexadienes were formed as minor products from 2- and 3-chlorotoluene, whereas a chloro- and methyl-substituted cyclohexadiene was the only product formed from 4-chlorotoluene. The toluene dioxygenase of P. putida F1 and chlorobenzene dioxygenase from Burkholderia sp. strain PS12 are the first enzymes described that efficiently catalyze the oxidation of 2-chlorotoluene.