Novel spectrophotometric approach for determination of validamycin A in fermentation of Streptomyces hygroscopicus

- A stable relationship between pigment secretion and Val-A production was found.
- An equation with SA value of pigment to determine Val-A was fitted.
- Accuracy and applicability of Spectrophotometry was proved in determining Val-A productivity and screening high-yield mutants.
- Spectrophotometry assay is reported first as a rapid method in antibiotic fermentation.

Validamycin A (Val-A), produced by Streptomyces hygroscopicus 5008 in industrial fermentation, is one of the most widely used anti-fungal agro-antibiotics in Asia and high performance liquid chromatography (HPLC) assay is usually used to determine the production of Val-A. A new approach to determine Val-A by spectrophotometer is developed. During the fermentation of S. hygroscopicus 5008, a pigment secretion was found along with the Val-A biosynthesis. There was a stable relationship between the concentration of Val-A and spectral absorption (SA) value of this pigment at 450 nm, even in different fermentation cultures or conditions. Using SA value as interior label, a rapid spectrophotometric method for determining Val-A production was established. In comparing Val-A productivity by HPLC method with that by SA method, the relative standard deviation (R.S.D.) was 0.007 (less than 0.05, no variation) and the conditional probability [Pr(T < t)] was 0.3491 (greater than 0.05, no difference) at the optimal time point of Val-A fermentation, which demonstrated SA method was as stable and accurate as standard HPLC method. It was applied successfully to finding positive strains with high Val-A productivity and short fermentation time. SA assay is an accurate and cost-effective method for measuring Val-A and screening high-producing strains, and this work provides a new insight for rapid quantitative analysis of antibiotics in fermentation of pigment-producing strains.