Utilization of quinate and p ‐hydroxybenzoate by actinomycetes: key enzymes and taxonomic relevance

474 strains of the actinomycete genera Streptomyces (including species of the former genera Chainia and Streptoverticillium ), Pseudonocardia and Micromonospora were examined for their ability to degrade quinate (Q) and p ‐hydroxybenzoate (pHB); selected strains were also tested for their capacity to catabolize benzoate (B). Whereas in the case of Q (5—10 g/l of a mineral salts agar medium) the growth response signalizes assimilation, pHB has to be supplied in lower concentration (routinely 0.3 g/l together with small amounts of peptone and yeast extract in liquid broth), and its degradation has to be determined spectrophotometrically. 27% of the streptomycete strains were able to grow with Q, and 57% with pHB. The three strains of “ Chainia ” that were tested metabolized Q and pHB, but none of the fourty species of “ Streptoverticillium ” showed this ability. 80% of the 30 strains of Psn. autotrophica grew with Q, and 100% degraded pHB and B. Two of the five Micromonospora strains gave a positive response with pHB, but not with Q. — Toluene treated cells (preincubated with Q, pHB or B, respectively) gave a positive Rothera reaction with protocatechuate or catechol respectively, thus demonstrating that these organisms employed the β‐ketoadipate pathway ( ortho ‐fission) for the degradation of Q, pHB and B. The assay of five relevant enzymes in cell‐free extracts of nine selected organisms showed that in nocardioform actinomycetes (Pseudonocardia, Rhodococcus) all enzymes of the protocatechuate branch of the ketoadipate pathway seem to be induced by β‐ketoadipate as demonstrated here for protocatechuate‐3,4‐dioxygenase. In contrast, in Streptomyces this enzyme appears to be induced by its substrate, protocatechuate, whereas the regulation of the other enzymes of this pathway remains to be elucidated.