Biosynthesis of Kitasamycin(Leucomycin) by Leucine Analog-Resistant Mutants of Streptomyces kitasatoensis

Abstract

The biosynthesis of kitasamycin in Streptomyces kitasatoensis B-896 was profoundly influenced by the addition of precursors to complex and defined media: l -valine and l -leucine directed biosynthesis towards the pairs A 4 /A 5 (R 2 = butyryl) and A 1 /A 3 (R 2 = isovaleryl), respectively, and total kitasamycin titers were doubled and quadrupled, respectively. S. kitasatoensis B-896 was very resistant (>20 mg/ml) to α-aminobutyric acid, an analog of l -valine, but very susceptible to l -leucine analogs 5′, 5′, 5′-trifluoroleucine and 4-azaleucine (5 to 10 μg/ml). The inhibition by 4-azaleucine could be reversed by l -leucine, but by none of the other amino acids of the pyruvate family or the amino acids of the aspartate pathway. 4-Azaleucine-resistant mutants were isolated which in the absence of any precursors overproduced l -leucine and a kitasamycin complex mainly consisting of the pair A 1 /A 3 . These 4-azaleucine-resistant mutants are presumed to be regulatory mutants in which α-isopropylmalate synthase, the first enzyme of the l -leucine pathway, has become either derepressed or desensitized to leucine feedback inhibition. l -Leucine-regulatory mutants have economic value: in the absence of expensive precursors, they produce a kitasamycin complex in which the most potent pair A 1 /A 3 is dominant and the least active components are absent.