Key enzymes for the degradation of benzoate,m- and p-hydroxybenzoate by some members of the order Actinomycetales

A preliminary screening of numerous species of the order Actinomycetales, especially of the genera Mycobacterium, Nocardia, Rhodococcus, Pseudonocardia, and Streptomyces, showed that many of them are able to metabolize benzoate (B) and p-hydroxybenzoate (pHB) as indicated by growth and change of color of the pH-indicator of an agar medium. Subsequent experiments with liquid cultures which allowed the analysis of substrate utilization by thin layer chromatography confirmed these results. The study of the degradative pathway proved that B was metabolized via catechol (C), pHB via protocatechuate (P) and m-hydroxybenzoate (mHB) via gentisate (G). The aromatic ring of C and P was subjected to an ortho-cleavage; only one strain of Noc. asteroides degraded C via a meta-cleavage, but P via an ortho-cleavage. Cell free extracts of four selected organisms exhibited activity of C-1,2-dioxygenase (C-1,2-O) and/or P-3,4-dioxygenase (P-3,4-O), depending on the growth substrate used for precultivation. In Streptomyces C-1,2-O was only found in cells grown on B, and P-3,4-O only in cells grown on pHB. On the contrary, in Rhodococcus rhodochrous B-cells oxidized C as well as P, while P-cells possessed only P-3,4-O-activity.