Phytic acid‐mediated regulation of secondary metabolism in Streptomyces thermoviolaceus grown in simple and complex media

Abstract

A.D. BRABBAN AND C. EDWARDS. 1997. Primary and secondary metabolism in the thermophilic actinomycete Streptomyces thermoviolaceus were found to be strongly regulated by phosphate in complex and defined media. Increasing phosphate levels in glutamate minimal salts media led to peak production of granaticin at 5 mmol phosphate, a concentration that was growth-limiting, before total inhibition of antibiotic production at 50 mmol. Product formation in particulate rapeseed meal-based media was found to be less affected by the initial phosphate concentration. The addition of 5 mmol phytic acid to proline minimal salts media led to an increase in the concentration of phosphate optimal for antibiotic production from 5.7 mmol to 15 mmol and reduced inhibition at higher concentrations. Phytic acid was shown to bind phosphate from minimal salts media and inhibit the growth of the organism at high concentrations. Differences in the production of granaticin by S. thermoviolaceus in two rapeseed meal-derived media were shown to be phosphate and phytic acid-related. In particulate rapeseed, the additional phosphate from minimal salts media was predominantly bound in an organic-soluble complex, while in extracted rapemeal media, phosphate was present predominantly in the free form. Overall, the work suggests that reduction in growth rate, which can be brought about by a variety of factors including low phosphate concentrations, is the critical factor for the onset of secondary metabolism in S. thermoviolaceus.