Physiological factors affecting the production of an antimicrobial substance by Streptomyces violatus in batch cultures

A survey was carried out to select an antibiotic producing Streptomyces strain isolated from garden soil in Alexandria, Egypt. Streptomyces violatus showed the highest antimicrobial activity in static cultures after 7 days incubation at 30°C. The antibacterial substance was more active against Bacillus subtilis and Staphyllococcus aureus than Escherichia coli or Sarcina lutea. Growth of S. violatus and production of antibiotic in a starch-nitrate medium were monitored over a period of 14 days. The organism produced a blue pigment associated with the antibiotic appearance in the cultures. Optimization of antibiotic production in batch cultures has been carried out. Substitution of starch by glycerol at a concentration of 12.5 g/l showed 1.32-fold increase of antibiotic production. Cultures containing sodium nitrate (2.5g/l) showed the highest antibiotic production followed by peptone, alanine, monosodium glutamate or phenylalanine. A mixture (w/w) of K2HPO4 and KH2PO4 (1g/l) yielded 1.9-fold and 6.1-fold increase in antibiotic production compared to cultures individually supplied with K2HPO4 or KH2PO4, respectively. The presence of ferrous sulphate and manganese chloride improved the production of the antibiotic. An inoculum size of 4x10 6 spores/ml and initial pH 7.0 at 30°C were optimum for a maximum antibiotic production of 268µg/ml in the culture filtrates of S. violatus.