Gentamicin formation in Micromonospora purpurea: stimulatory effect of ammonium

The effect of ammonium on the fermentative production of gentamicin in Micromonospora purpurea has been studied using a chemically defined medium. Ammonium chloride concentrations ranging from 20 to 150 mM resulted in a proportional stimulation of growth and antibiotic formation. The use of other ammonium salts exerted a similar effect. Among the products of ammonium assimilation, glutamate and glutamine were able to exert the stimulatory effect. In addition, both amino acids reproduced the stimulation in resting cell systems of this microorganism and this result was not modified by the presence of chloramphenicol, eliminating a possible inductive action as the cause of this effect. The use of a glutamine synthetase inhibitor prevented antibiotic formation. This inhibition was reverted only by glutamine, suggesting that this amino acid was responsible of ammonium stimulation. Glutamine stimulation seems to be due to its ability to produce 2-deoxystreptamine and glucosamine, intermediates of the gentamicin biosynthetic pathway.