Physiological studies on gentamicin: phosphate repression of antibiotic formation

The effect of inorganic phosphate on the fermentative production of gentamicin by Micromonospora purpurea has been studied using a chemically defined medium. Phosphate concentrations higher than 5.75 mM (1 g/liter-1) did not inhibit growth but specifically prevented antibiotic formation. Changes in the pH medium and carbon or nitrogen depletion were excluded as the cause of antibiotic underproduction. The use of a phosphate analogue, a protein synthesis inhibitor and the profiles of differential rate of antibiotic production suggested that phosphate itself transiently repressed gentamicin formation. Phosphate affected the formation of 2-deoxystreptamine from 2-deoxyinosose, a none phosphorylated substrate.