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

Primary and secondary metabolism in the thermophilic actinomycete Streptomycesthermoviolaceus were found to be strongly regulated by phosphate in complexand defined media. Increasing phosphate levels in glutamate minimal salts media led to peakproduction of granaticin at 5 mmol phosphate, a concentration that was growth-limiting, beforetotal inhibition of antibiotic production at 50 mmol. Product formation in particulate rapeseedmeal-based media was found to be less affected by the initial phosphate concentration. Theaddition of 5 mmol phytic acid to proline minimal salts media led to an increase in theconcentration of phosphate optimal for antibiotic production from 5·7 mmol to 15 mmol andreduced inhibition at higher concentrations. Phytic acid was shown to bind phosphate fromminimal salts media and inhibit the growth of the organism at high concentrations. Differences inthe production of granaticin by S. thermoviolaceus in two rapeseed meal-derived mediawere shown to be phosphate and phytic acid-related. In particulate rapeseed, the additionalphosphate 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 varietyof factors including low phosphate concentrations,is the critical factor for the onset of secondarymetabolism in S.thermoviolaceus.