Screening and functional study of Bacillus from intestines of largemouth bass
In order to screen Bacillus strains which are beneficial to largemouth bass,the Bacillus strains from the intestine of largemouth bass were isolated,their hemolysis,enzymatic activity,biofilm for-mation ability,sensitivity to various common antibiotics,tolerance to gastric and intestinal fluids,and in vitro antagonism against Nocardia were detected.These strains were added to the feed of largemouth bass and weigh gain and expression of inflammatory cytokine were detected.A total of 94 Bacillus strains were identified.Four Bacillus subtilis strains,K-3,K-12,K-13,and K-22,were selected based on their non-hemolytic and broad enzymatic activity.These four strains all formed strong biofilms and were sensitive to various common antibiotics.Strains K-3 and K-13 showed in vitro antagonism against Nocardia.The 2-hour survival rates of the four strains in artificial gastric and intestinal fluids were above 80%.After feeding for 42 days,the weight gain of largemouth bass of K-13 group was significantly higher than that of the con-trol group,while protease and lipase activities in the intestines in K-12 and K-13 groups were significantly higher than that of the control group.In addition,compared with the control group,the expression levels of pro-inflammatory factors in the head kidney,spleen,and hind gut of the K-13 experimental group were down-regulated,while the expression levels of anti-inflammatory factor were up-regulated,indicating that K-13 has the potential to reduce intestinal inflammation in largemouth bass.Overall,the B.subtilis strain K-13 selected in this study has high safety,broad enzymatic activity,antagonism against Nocardia,and promotes the growth of largemouth bass,making it a potential probiotic additive for largemouth bass feed.
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