Enhance the biocontrol efficiency of Bacillus velezensis Bs916 for white spot syndrome virus in crayfish by overproduction of cyclic lipopeptide locillomycin

White spot disease, caused by white spot syndrome virus (WSSV), is a serious crustacean disease in China, and currently, there is no specific treatment for it. In this study, the addition of locillomycin could help to improve the cumulative survival rate of WSSV-infected crayfish. Then further analysis showed that Spo0A and SpoIIID could negatively regulate the production of locillomycin in Bacillus velezensis Bs916, and the disruption of them caused a significant increase in the production of locillomycin, which was 8.9 times higher than that of wild-type. Subsequently, we investigated the protective effects of B. velezensis Bs916 and Delta Spo0A + SpoIIID as probiotics, and the results showed that addition of their cultures to the basal control diet significantly reduced the mortality of WSSV-challenged crayfish. Further results indicated that dietary B. velezensis Bs916 or Delta Spo0A + SpoIIID supplement reduced the copy number of WSSV and improved the immune activities of acid phosphatase (ACP), alkaline phosphatase (AKP), nitric oxide synthase (NOS) and lysozyme (LZM) in crayfish. Moreover, compared with B. velezensis Bs916, all above performances were further enhanced when Delta Spo0A + SpoIIID was provided, so we speculated that overproduction of locillomycin might contribute to the enhancement of biocontrol efficiency of B. velezensis Bs916 for WSSV in crayfish. In summary, this study provides some insight into the therapeutic or prophylactic intervention with B. velezensis Bs916 or its metabolic product, locillomycin, to protect crayfish against WSSV infection, and also provides a theoretical basis for the construction of high yielding locillomycin strains.

Automated summary

White spot disease caused by white spot syndrome virus (WSSV) is a serious crustacean disease in China. Addition of locillomycin could improve the survival rate of WSSV-infected crayfish. Spo0A and SpoIIID were found to negatively regulate the production of locillomycin in Bacillus velezensis Bs916, and disruption of them increased the production of locillomycin significantly. Feeding with B. velezensis Bs916 or Delta Spo0A + SpoIIID reduced the mortality of WSSV-challenged crayfish and improved their immune activities.