The killer yeast wickerhamomyces anomalus is a potential new tool for the symbiotic control of malaria

Introduction Wickerhamomyces anomalus is a yeast associated with different insects including disease vector mosquitoes and sandflies (Ricci et al. 2011; Martin et al. 2015), where it is proposed to be involved in symbiotic relationships with hosts (Cappelli et al. 2014; Martin et al. 2018). Different symbiotic strains of W. anomalus display a killer phenotype mediated by protein toxins with broad-spectrum antimicrobial activities. In particular, a killer toxin (KT) purified from a W. anomalus strain (WaF17.12), isolated from the malaria vector mosquito Anopheles stephensi, has shown anti-plasmodial activities against early sporogonic stages of the murine malaria parasite Plasmodium berghei. Methods WaF17.12 was cultured in selective conditions to stimulate KT production. Supernatants were separated by chromatography and analysed using an antibody specific for yeast KTs. Food preparation containing activated WaF17.12 was provided to An. stephensi. The effect of WaF17.12-KT was tested using P. berghei transgenic strains that express Green Fluorescent Protein. Twenty-four hours after the infected blood meal, mosquito guts were analysed through fluorescence microscopy to detect early sporogonic stages. Results WaF17.12 cultures, properly stimulated to induce the KT expression, affect P. berghei early sporogonic stages in the mosquito midgut lumen, causing parasite membrane damage and death. A mosquito dietary supplementation with activated WaF17.12 cells, strongly interfere with the ookinete development, significantly reducing the parasite number. Discussion Innovative biotechnologies propose novel tools for the prevention of insect-borne diseases as the Symbiotic Control (SC), which implies the use of microbial symbionts living in insects to block pathogens transmission. Symbionts can be used as a Trojan horse to drive antagonist molecules in the vector’s gut, interfering with pathogens proliferation. WaF17.12 might be a good candidate for SC and its strong anti-plasmodial activity, observed in our study, outlines further investigations in wild vectors, that could lead to innovative, safe and cost-competitive tools against malaria