Biochemical and Genetic Characterization of Streptomyces rimosus Mutants Impaired in Oxytetracycline Biosynthesis

Abstract

Antibiotic non-producing mutants were isolated from an oxytetracycline (OTC) producing strain of Streptomyces rimosus. Cosynthesis tests and feeding known intermediates of the OTC pathway allowed the classification of the mutants into several groups. The biosynthetic lesion was determined for several of the mutants. Some of the mutants deficient in the reduction of 5a, 11a-dehydrooxytetracycline, the final step in the pathway, were unable to synthesize a cofactor (CSF1) essential for this reaction. Mutations apparently in genes for enzymes of the main OTC pathway were found for three of a possible four steps between 4-aminodedimethylaminoanhydrotetracycline (4-amino-ATC) and OTC. Mutations affecting three other steps of a possible five before 4-amino-ATC were found, but unambiguous identification of these was not possible. The genes for OTC production, including those for CSF1 synthesis, were located in two diametrically opposite clusters on the S. rimosus chromosomal linkage map. No evidence for plasmid-borne genes was obtained.