GENETIC APPROACH TO BIOSYNTHESIS OF RIFAMYCIN-CHROMOPHORE IN NOCARDIA-MEDITERRANEI .1. ISOLATION AND CHARACTERIZATION OF A PENTOSE-EXCRETING AUXOTROPHIC MUTANT OF NOCARDIA-MEDITERRANEI WITH DRASTICALLY REDUCED RIFAMYCIN PRODUCTION

The mutant under study, designated A8, is derived from a Nocardia mediterranei strain, N813, which is a high rifamycin B producer. A8 is auxotrophic for aromatic amino acids and produces much less rifamycin B than the parent. A mixture of pentoses with D (−) ribulose as the main product is accumulated in the fermentation broth of this mutant. It was shown to be affected in its transketolase activity as no formation of D-sedoheptulose-7P from pentosephosphates could be detected in vitro using crude extracts. The only pathway so far known which is derived from D-sedoheptulose-7P is the shikimate pathway leading to aromatic amino acids and vitamins. Biochemical and genetic investigations with mutant A8, which is defective in both the biosynthesis of rifamycins and the biosynthesis of shikimate pathway products, show that the seven-carbon amino unit of the rifamycinchromophore must be derived from an intermediate of the shikimate pathway. © 1978, JAPAN ANTIBIOTICS RESEARCH ASSOCIATION. All rights reserved.