Production, purification, and antifungal activity of the antibiotic nucleoside, tubercidin, produced by Streptomyces violaceoniger

Abstract

Three antibiotic substances strongly inhibitory to Phytophthora capsici or Magnaporthe grisea were isolated from the broth culture of Streptomyces violaceoniger strain A50. A butanol-soluble mixture of antibiotics from the broth were partially purified by XAD-2 column chromatography. The XAD-2 eluates inhibited the mycelial growth of P. capsici and M. grisea and the development of Phytophthora blight on pepper (Capsicum annuum L.) plants. The antibiotics were separated by silica gel column chromatography and then purified on a Sephadex LH-20 column to yield three peaks of antifungal activity: SF1A, SF1B, and SF2A. The pure antibiotic SF2A was further purified by preparative HPLC and identified as the pyrrolo[2,3-d]-pyrimidine nucleoside tubercidin based on the UV, 1H, and 13C NMR spectral data and other chemical evidence. The antibiotic SF2A and authentic tubercidin showed a high antifungal activity against the plant pathogenic fungi P. capsici, Botryosphaeria dothidea, and Rhizoctonia solani. Key words: Streptomyces violaceoniger, tubercidin, antifungal activity.