Biodegradation of dimethylphenols by bacteria with different ring-cleavage pathways of phenolic compounds.

The biodegradation of 3,4, 2,4, 2,3, 2,6 and 3,5-dimethylphenol in combination with phenol and p-cresol by axenic and mixed cultures of bacteria was investigated. The strains, which degrade phenol and p-cresol through different catabolic pathways, were isolated from river water continuously polluted with phenolic compounds of leachate of oil shale semicoke ash heaps. The proper research of degradation of 2,4 and 3,4-dimethylphenol in multinutrient environments was performed. The degradation of phenolic compounds from mixtures indicated a flux of substrates into different catabolic pathways. Catechol 2,3-dioxygenase activity was induced by dimethylphenols in Pseudomonas mendocina PC1, where meta cleavage pathway was functional during the degradation of p-cresol. In the case of strains PC18 and PC24 of P. fluorescens, the degradation of p-cresol occurred via the protocatechuate ortho pathway and the key enzyme of this pathway, p-cresol methylhydroxylase, was also induced by dimethylphenols. 2,4 and 3,4-dimethylphenols were converted into the dead-end products 4-hydroxy-3-methylbenzoic acid and 4-hydroxy-2-methylbenzoic acid. In the degradation of 3,4-dimethylphenol, the transient accumulation of 4-hydroxy-2-methylbenzaldehyde repressed the consumption of phenol from substrate mixtures. A mixed culture of strains with different catabolic types made it possible to overcome the incompatibilities at degradation of studied substrate mixtures.