earticle

영어

Validamycin A or called as jinggangmycin in China is an anti-fungal aminoglycoside antibiotic produced by Streptomyces hygroscopicus var. limoneus and S. hygroscopicus var.
jingganggensis 5008 (S. hygroscopicus 5008, hereafter). Because of its high protection efficiency and safety to human and animals, validamycin A has been one of the most important and widely used plant protection reagents for the treatment of rice sheath blight disease in East Asia. In this work, the effects of fermentation temperature on validamycin A biosynthesis by S. hygroscopicus 5008 were investigated within 28-42oC in detail, and an interesting threshold of temperature for the antibiotics production was found between 35oC and 37oC. At a relatively higher temperature, a much higher validamycin A productivity was obtained together with faster protein synthesis and sugar consumption. Transcription analysis of samples from early, middle and late stages of fermentation at various temperatures demonstrated that three operons, valABC, valKLMN and valG, for all eight necessary structure genes, were dramatically promoted when temperature reached the threshold. Activities of both glucose-6-phosphate dehydrogenase (G6PDH) of pentose-phosphate pathway and ValG of validamycin A biosynthesis were also enhanced at a higher cultivation temperature. The interesting temperature effect with a 2oC threshold shift from 35oC to 37oC on the antibiotic biosynthesis was understood in view of the gene transcription levels and key enzyme activities. In addition, reactive oxygen species (ROS) are generated during fermentation, and it is reported that ROS mediate many cell processes in different organisms. In this work, H2O2 induced ROS was found to regulate the validamycin A biosynthesis, and H2O2 stress was an effective strategy in enhancing the validamycin A fermentation. The new information obtained will be helpful to industrial production of this important antibiotic.