Production of 3,4-dihydroxyphthalate from phthalate by a membrane-bound two-enzyme system from Rhodococcus erythropolis

Bacterial degradation of phthalate isomers and their esters

Phthalate isomers and their esters are used heavily in various industries. Excess use and leaching from the product pose them as major pollutants. These chemicals are toxic, teratogenic, mutagenic and carcinogenic in nature. Various aspects like toxicity, diversity in the aerobic bacterial degradation, enzymes and genetic organization of the metabolic pathways from various bacterial strains are reviewed here. Degradation of these esters proceeds by the action of esterases to form phthalate isomers, which are converted to dihydroxylated intermediates by specific and inducible phthalate isomer dioxygenases. Metabolic pathways of phthalate isomers converge at 3,4-dihydroxybenzoic acid, which undergoes either ortho- or meta- ring cleavage and subsequently metabolized to the central carbon pathway intermediates. The genes involved in the degradation are arranged in operons present either on plasmid or chromosome or both, and induced by specific phthalate isomer. Understanding metabolic pathways, diversity and their genetic regulation may help in constructing bacterial strains through genetic engineering approach for effective bioremediation and environmental clean up.

o-, m- and p-hydroxybenzoate degradative pathways in Rhodococcus erythropolis

Rhodococcus erythropolis strain S1 uses the gentisate pathway to metabolize salicylate and m-hydroxybenzoate and the protocatechuate pathway to degrade p-hydroxybenzoate. m-Hydroxybenzoate 6-hydroxylase was induced by growth on m-hydroxybenzoate or gentisate, and salicylate 5-hydroxylase only by growth on salicylate. p-Hydroxybenzoate 3-hydroxylase could be induced only by growth on p-hydroxybenzoate. m-Hydroxybenzoate or p-hydroxybenzoate could repress the induction of salicylate 5-hydroxylase. Maleylpyruvate isomerase in the gentisate pathway did not require reduced glutathione.