Bacillus subtilis expressing double-strand RNAs (dsRNAs) induces RNA interference mechanism (RNAi) and increases survival of WSSV-challenged Litopenaeus vannamei

Abstract

Despite the great commercial success, the Pacific white shrimp Litopenaeus vannamei farming has suffered great economic losses due to the impact of viral diseases such as White Spot Syndrome. Among the innovative ap-proaches to mitigate viral diseases, one of the most promising is the manipulation of the eukaryote process known as interfering RNA (RNAi). This natural mechanism can be induced to improve degradation of viral transcripts, through double-stranded RNA molecules (dsRNAs) homologous to key target genes. The synthetic production of such molecules is expensive and prevents the use of this technology on a large scale. In the present study, the probiotic Bacillus subtilis was engineered to produce dsRNAs against the WSSV vp28 gene transcripts. The results obtained showed that the dsRNAs produced by the probiotic are efficient in inducing the RNAi mechanism in shrimp hemocytes. Shrimp pretreated with the genetically reprogrammed probiotic had a higher survival rate when challenged with the virus, and showed a considerable decrease in viral load. Histological analyzes did not identify viral inclusions in the survivors’ cuticle, gills and gastric epithelium. The present study reports that probiotics can be reprogrammed for the production of antiviral dsRNAs and that these molecules are absorbed at the intestine and reach the shrimp’s hemocytes, minimizing viral replication. Despite the current restrictions on the use of genetically modified microorganisms, this technology can become an important ther-apeutic tool not only for aquacultured species, but also for the treatment of human diseases in the near future.