Killer yeasts exert anti-plasmodial activities against the malaria parasite Plasmodium berghei in the vector mosquito Anopheles stephensi and in mice

Alessia Cappelli,Irene Ricci,Jovana Bozic,Consuelo Amantini,Paolo Rossi,Valentina Cecarini,Guido Favia,Priscilla Mensah,Matteo Valzano

doi:10.1186/s13071-019-3587-4

Abstract

BackgroundWickerhamomyces anomalus is a yeast associated with different insects including mosquitoes, where it is proposed to be involved in symbiotic relationships with hosts. Different symbiotic strains of W. anomalus display a killer phenotype mediated by protein toxins with broad-spectrum antimicrobial activities. In particular, a killer toxin purified from a W. anomalus strain (WaF17.12), previously isolated from the malaria vector mosquito Anopheles stephensi, has shown strong in vitro anti-plasmodial activity against early sporogonic stages of the murine malaria parasite Plasmodium berghei.ResultsHere, we provide evidence that WaF17.12 cultures, properly stimulated to induce the expression of the killer toxin, can directly affect in vitro P. berghei early sporogonic stages, causing membrane damage and parasite death. Moreover, we demonstrated by in vivo studies that mosquito dietary supplementation with activated WaF17.12 cells interfere with ookinete development in the midgut of An. stephensi. Besides the anti-sporogonic action of WaF17.12, an inhibitory effect of purified WaF17.12-killer toxin was observed on erythrocytic stages of P. berghei, with a consequent reduction of parasitaemia in mice. The preliminary safety tests on murine cell lines showed no side effects.ConclusionsOur findings demonstrate the anti-plasmodial activity of WaF17.12 against different developmental stages of P. berghei. New studies on P. falciparum are needed to evaluate the use of killer yeasts as innovative tools in the symbiotic control of malaria.

Highlights

Wickerhamomyces anomalus is a yeast associated with different insects including mosquitoes, where it is proposed to be involved in symbiotic relationships with hosts
Such data suggests that the effect of W. anomalus on P. berghei sporogonic stages development was strain-dependent and attributable to the presence of the killer toxin (KT) in the medium
To assess the activation of the WaF17.12 strain and to confirm KT expression, the supernatants from both strains were separated by ion-exchange chromatography and obtained fractions were analysed by western blot as described in the material and methods section

Summary

Introduction

Wickerhamomyces anomalus is a yeast associated with different insects including mosquitoes, where it is proposed to be involved in symbiotic relationships with hosts. Plasmodium has a complex life-cycle including sexual and asexual developmental stages It alternates a sporogonic phase in the mosquito with differentiation of zygotes, ookinetes, oocysts and sporozoites, and hepatic/erythrocytic phases in the vertebrate host where it multiplies different asexual stages, micro- and macro-gametocytes. This multifaceted phenotypic variability is advantageous for the parasite but hampers. Some bacteria, including Asaia, Wolbachia and Pantoea, and fungi such as Metarhizium, have been proposed for the SC of malaria [3, 6,7,8] In this frame, the identification of killer yeasts that exert symbiotic functions in mosquitoes is very promising [9, 10]

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