Abstract
The effects of aeration-agitation conditions and mediumcomposition on colistin fermentation were investigated with 5 liter-jar fermentors, using a medium containing aspartic acid. Since the high viscosity of the culture at 28°C lowered the aeration-agitation effect, a lower viscous culture at 32°C was used. The aeration-agitation conditions on a 5 liter-jar scale were determined with agitation. Although an increase of sugar concentration improved colistin production, an increase of broth viscosity or agitation speed limited colistin production. On the other hand, ammoniumnitrogen (NH4-N) was found out to control not only the optimum ratio of carbon to nitrogen for colistin production but the broth viscosity. The optimum ratio of sugar (as glucose) to NH4-N in the colistin fermentation was about 10 : 4. The optimumphosphate concentration for colistin production was independent of the agitation speed.
Bacillus polymyxa var. KY-7584 produced 71, 000u/ml of colistin in the modified medium containing the optimum levels of sugar and NH4-Nat 32°C. This titer corresponded to an increment of about 30% compared with the maximumtiter in the reference medium at 28°C (55, 500u/ml), and also was about five times as much as that in Morido's medium (14, 800u/ml) used as the basal medium.
