Efficient Utilization Of Oil Cakes As Raw Material For Bacitracin Fermentation

Bacitracin,composed of 12 amino acids,is a kind of polypeptide antibiotic.The main producing strain is Bacillus licheniformis.It is a novel broad-spectrum antibiotic at present that is used extensively in the feed additive.In this paper,bacitracin fermentation with oil cakes by Bacillus licheniformis DW2 were optimized.The effects of amino acids on bacitracin fermentation was studied,which provided guidance for the fermentation production of bacitracin.This paper investigated the effect of different oil cakes on bacitracin fermentation.The single factor experiments on the basis of the original fermentation medium led to the conclusion that the optimum concentration of soybean meal was 10%.Then bacitracin fermentation feedstock had been optimized,the results indicated that soybean meal powder was the best single nitrogen source.The bacitracin titer was increased when mixed with other oil cakes,and ultimately the optimum ratio of nitrogen sources for bacitracin fermentation was 7%soybean meal + 2%low protein rapeseed cake.The titer of bacitracin reached 910.4 u/mL in 250 mL shake flask,which increased by 20.5%compared to the original formula.And the titer reached 849.3 u/mL with the ratio of bacitracin A being 64.0%in 50 L fermenter.Compared with CK,the titer and the ratio of A component increased by 12.4%and 6.8%respectively.This paper analyzed amino acid metabolism of bacitracin fermentation by measuring intracellular and extracellular amino acid content during the fermentation process.Results showed that Cys was the limiting amino acid of bacitracin fermentation.The titer of bacitracin was increased 7.5%by addition of 0.08 g/L Cys at 24 h,which indicated that Cys really could promote bacitracin synthesis.In addition,adding appropriate amounts of Ile,Glu,Lys,soybean meal hydrolysate and rapeseed cake hydrolysate at 24 h in fermentation medium could increased the yield of bacitracin in varying degrees.Through comparison to the proportion of various amino acids in soybean meal and rapeseed cake,it could be found that the proportion of Glu、Pro、Cys in rapeseed cake was 2.58%,2.50%,1.01%respectively higher than that in soybean meal.Thus one of the reasons that soybean meal combined with rapeseed cake had a good effect might be that increasing the proportion of Glu and Cys under the same nitrogen content could promote bacitracin synthesis.This paper also studied the effect of three areas including A,B，C of soybean meal and four kinds of particle size including 60 mesh,80 mesh,100 mesh，200 mesh of soybean meal on bacitracin fermentation.Differences in the amino acid composition and the hydrolysis degree were compared respectively.The results showed that soybean meal from C was best,and the total amino acid content was the highest.In addition to Lys and His,the contents of other amino acids were also the highest.Soybean meal with granularity of 80 mesh was best for bacitracin fermentation.The particle size of soybean meal was finer,the total degree of hydrolysis and leaching rate of protein was greater，but the yield of bacitracin was not necessarily higher.