The metabolic divergence in the meta cleavage of catechols by Pseudomonas putida NCIB 10015. Physiological significance and evolutionary implications.

Abstract

A reinvestigation of the catabolic pathway(s) used by Pseudomonas putida NCIB 10015 (Dagley's strain) for the degradation of phenol and the cresols has proved the existence of a metabolic divergence after meta cleavage of the catechols formed by hydroxylation of the primary substrates. The ring‐fission products of catechol and 4‐methylcatechol are shown to be simultaneously catabolized by two different enzymic activities, an NAD+‐dependent dehydrogenase and a cofactor‐independent hydrolase. The metabolizing activities of both ring‐fission products in extracts of cells grown on phenol and the cresols (o‐, m‐ and p‐cresol) were found to be non specific; thermal inactivation of extracts of phenol‐grown cells has shown that this nonspecificity is attributable to only one enzyme expressing each activity and that the two activities are located on separate proteins. Extracts of cells grown on all four substrates contain high induced levels of the meta cleavage suite of enzymes functional in the dissimilation of catechol, including both the 4‐oxalocrotonate branch (NAD+‐dependent 2‐hydroxymuconic semialdehyde dehydrogenase, 4‐oxalocrotonate tautomerase and 4‐oxalocrotonate decarboxylase) and the hydrolytic branch (2‐hydroxymuconic semialdehyde hydrolase). The hydroxylase, oxygenase, dehydrogenase and hydrolase activities are shown to be nonspecific and can also act upon the methyl derivatives of their respective substrates. A constant pattern of specificity was found for these enzymes, independent of the monophenolic substrate used for growth. From studies with a mutant lacking phenol hydroxylase, the entire suite of meta cleavage enzymes are shown to be coincidently induced from the top by the primary substrate (phenol or the cresols). The evolutionary and physiological implications of the divergent pathway are discussed.