Colistin Sulfate Strain Selection And Fermentation Process

The Polymyxin, also named colistin or colomycin, is a polypeptide system antibiotic abstracted from the fermentation broth. It is a mixture of polymyxin El and polymyxin E2, slightly soluble in water, white crystal or crystalline powder. The sulfate of colistin is a white powder, freely soluble in water,slightly soluble in methanol and ethanol, insoluble in acetone and acether, stable under pH of 2.0-6.0 and heat. It is slightly absorbed in animal digestive tract and quickly excreted with slightly toxicity and little side-effect, and thus it is one of the safest antibiotic to promote the growth of animals.In this article, a colistin producing strain originated from Paenibacillus polymyxa 6^# was treated by UV and a stable and high-yielding mutant 37# was screened out, the productivity of which was increased by 15%. Then the mutant which cultured on media containing α-amino-butyric acid (the analogue of valine) was treated with NTG, the mutant 42^# was obtained with the titer of colistin increased by 18% than the original strain.The fermentation condition of colistin production was optimized using shaking flask. The ratio of mixed carbon nutrition of 10% glucose and 90% soluble starch and mixed nitrogen nutrition of 0.1% (NH₄)₂SO₄ and the organic nitrogen of wheat embryo power was 2.5:1. The optimal culture time for seed was 20 to 24 hours;the optimal inoculation amount was 6% and the origin pH value was controlled under 6.4-6.6.The effects of environmental conditions on colistin production were investigated. The fermentation condition was further optimized on the 18m³ fermentor. The optimized fermentation conditions were as follows: aeration ratio 0.8m³/m³ min, stir speed 150rpm and the fermentation temperature 33 ℃。 The unit of fermentation broth was increased by 33% and the volumes 6% when fermenting procedure was ended.