High-density Fermentation Of Bacillus Cereus And The Effect On Intestinal Flora

Bacillus cereus is a bacterium that can produce a variety of active substances,improve and treat a variety of gastrointestinal diseases,and enhance host immunity.Studies have shown that Bacillus cereus can balance the intestinal flora,but there are few studies on its mechanism of regulating the intestinal flora.For Bacillus probiotics,colony count and spore rate have a great influence on their probiotic functions.At present,there are relatively few reports on improving the yield of Bacillus cereus,and the reported yield is low.Therefore,it is necessary to optimize the fermentation process of Bacillus cereus to improve its yield and spore rate.It is also necessary to explore how Bacillus cereus regulates the gut microbiota and the influence of daily diet on this regulation.Given the above problems,this paper optimizes the culture conditions and fermentation strategy of Bacillus cereus.Finally,the yield of Bacillus cereus was higher than the reported level.For the first time,the bionic large intestine reactor independently developed by our laboratory was used to explore the regulation of Bacillus cereus on the intestinal flora,and the effects of different diets on this regulation.The main research results are as follows:（1）The optimized fermentation medium formula(g·L^-1):glucose 12.5,water-soluble starch 12.5,soy peptone 10.0,yeast extract 10.0,Mn Cl₂ 0.6,Mg SO₄·7H₂O 3.0,（NH₄）₂SO₄ 3.0.（2）The fermentation strategy at the 7 L fermenter level is as follows:0-9 h,the constant stirring speed,aeration ratio,and p H were 250 r·min^-1,1.0 vvm,and 6.5.After 9 h,the carbon and nitrogen sources were added at a rate of 0.45 m L·min^-1.At the same time,the stirring speed and aeration ratio were increased to 350 r·min^-1 and 1.5 vvm.At 18 h,the flow of carbon and nitrogen sources were stopped.Simultaneously,the p H,stirring speed,and aeration ratio were changed to 7.5,150 r·min^-1,and 0.75 vvm.Under this control strategy,the viable count of Bacillus cereus reached 2.2×10¹⁰ CFU·m L^-1,which was higher than the reported yield.The spore rate was more than 90.0%at the end of fermentation.（3）The vitro simulated digestion test showed that Bacillus cereus still had a survival rate of 39.78±6.42%after being digested by simulated saliva,gastric juice,and small intestinal juice.The experimental results indicated that Bacillus cereus could effectively tolerate the gastrointestinal environment.（4）The changes in the production of lactic acid and short-chain fatty acids（SCFAs）showed that the production of lactic acid and SCFAs increased significantly after adding Bacillus cereus.The production of lactic acid and SCFAs in different dietary groups was measured.The high carbohydrate group（HC）was found to have the highest production of lactic acid and acetic acid,reaching 66.63 and 71.75 mmol·L^-1,respectively.The high protein group（HP）had the highest propionic acid production,reaching 73.26 mmol·L^-1.Only the high-fat group（HF）produced butyrate.The experimental results showed that Bacillus cereus can effectively promote the production of intestinal lactic acid and SCFAs,and different diets have different degrees of influence on this effect.（5）The results of bacterial community structure analysis showed that,after the addition of Bacillus cereus,the relative abundance of harmful intestinal bacteria（Shigella,Clostridium erysipelas,Clostridium,etc.）decreased,and the relative abundance of beneficial intestinal bacteria（Lactobacillus,Bacteroides,Bifidobacterium,etc.）increased.The experimental results showed that Bacillus cereus could achieve its probiotic effect by regulating the composition of intestinal flora.