Baci-VAC, a novel RNAi vaccine from a non-pathogenic Bacillus subtilis cell expressing dsRNA-EHP to protect microsporidian infection in shrimp

Disease presents a significant challenge in global shrimp aquaculture. Ecytonucleospora (=Enterocytozoon) hepatopenaei (EHP) is a prominent microsporidian menace to this industry. Effective vaccines are essential for safeguarding shrimp against pathogens. Long dsRNA, which stimulates RNA interference (RNAi), can activate innate immune pathways and an RNAi-like mechanism in a marine shrimp. RNA interference vaccines present a promising, eco-friendly solution. We focus on harnessing Bacillus subtilis, a well-described probiotic that supports shrimp health, to produce double-stranded RNA (dsRNA). B. subtilis possesses a well-established secretion system that facilitates the release of dsRNA. We propose to engineer B. subtilis to produce dsRNA and silence crucial genes in EHP. Our strategy involves synthesizing dsRNA that can target the polar tube extrusion protein of EHP, a protein that plays a key role in development and infectivity – where it initiates the intracellular life cycle and generation of mature spores, disrupting sporogony. DsRNA from B. subtilis will be introduced to shrimp before they are infected with EHP, allowing the RNAi mechanism process within the shrimp. This intervention has the potential to enhance shrimp health, bolster resistance to pathogen infection, and promote shrimp growth. Shrimp cells have been shown to express the SID-1 complex, allowing for dsRNA uptake, meaning that each cell can uptake the anti-microsporidian dsRNA product and become resistant. By developing a dsRNA-secreting strain of B. subtilis, we aim to achieve high-yield dsRNA production in an environmentally sustainable manner, reducing production costs and using a compound deemed safe for both shrimp and human consumption. This innovation offers hope for utilizing dsRNA in aquaculture systems to combat shrimp diseases and promote sustainable farming. This project proposes a first step towards demonstrating the feasibility of using dsRNA from B. subtilis to prevent EHP in shrimp, laying the groundwork for using dsRNA-secreting Bacillus in the future.