Isolation and Identification of Bacillus subtilis LJ and Its Control Effect Against Vibriosis in Litopenaeus vannamei Larvae
[Objective]To isolate and identify probiotics that antagonize pathogenic vibrios from shrimp intestines,and evaluate its biological safety and control effect against vibriosis in Litopenaeus vannamei larvae,so as to promote the prevention and bioconrol of shrimp vibriosis by probiotics.[Method]Shrimp intestinal bacteria were isolated by using streak plate method,and from which potential probiotic was screened based on antagonistic activity against pathogenic vibrios.The target strain was identified according to the phenotypical characteristics,16S rRNA and rpoB gene sequences,and its sensitivities to 17 kinds of antibacterial drugs were examined by disc diffusion method.The biocontrol effect of L.vannamei larvae infected with Vibrio parahaemolyticus was evaluated by adding target bacteria to water.[Result]A strain named LJ with obvious antagonism against V.parahaemolyticus,Vibrio harveyi,and Vibrio campbellii was isolated and selected from shrimp intestines.LJ has no multiple drug resistance and was identified as Bacillus subtilis.The addition of 1×105 and 1×106 cfu/mL LJ to water could significantly improve the survival and metamorphosis rates of shrimp larvae infected with V.parahaemolyticus(P<0.05),and the high-dose treatment group had a more significant effect.Under conditions without pathogen infection,high concentration of LJ(5×107 cfu/mL)was harmless to larvae and could significantly promote their survival and metamorphosis.[Conclusion]The B.subtilis LJ derived from shrimp gut has high biosafety,can effectively antagonize pathogenic vibrios and improve the survival rate of L.vannamei larvae infected with V.parahaemolyticus.
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