Cloning, expression and medium optimization of validamycin glycosyltransferase from Streptomyces hygroscopicus var. jinggangensis for the biotransformation of validoxylamine A to produce validamycin A using free resting cells

► Cloning and expression of valG from Streptomyces hygroscopicus var. jinggangensis. ► Biotransformation of validoxylamine A to validamycin A with cellobiose as the sugar donor. ► Using resting cells instead of validamycin glycosyltransferase. ► Improving the content of validamycin A in the products. ► Effective optimization of the culture medium with response surface methodology.