Abstract
The yeast Wickerhamomyces anomalus has several applications in the food industry due to its antimicrobial potential and wide range of biotechnological properties. In particular, a specific strain of Wickerhamomyces anomalus isolated from the malaria mosquito Anopheles stephensi, namely WaF17.12, was reported to secrete a killer toxin with strong anti-plasmodial effect on different developmental stages of Plasmodium berghei; therefore, we propose its use in the symbiotic control of malaria. In this study, we focused on the identification/characterization of the protein toxin responsible for the observed antimicrobial activity of the yeast. For this purpose, the culture medium of the killer yeast strain WaF17.12 was processed by means of lateral flow filtration, anion exchange and gel filtration chromatography, immunometric methods, and eventually analyzed by liquid chromatography-tandem mass spectrometry (LC–MS/MS). Based on this concerted approach, we identified a protein with a molecular weight of approximately 140 kDa and limited electrophoretic mobility, corresponding to a high molecular weight β-glucosidase, as confirmed by activity tests in the presence of specific inhibitors.
Highlights
Killer yeasts can secrete one or several kinds of toxins with peculiar molecular weights and post-translational modifications, which are able to kill sensitive cells of the same or related yeast genera in the absence of a direct cell-cell contact [1]
Most killer toxins exert their activity on sensitive cells via a two-step mechanism: they bind to primary receptors, mainly β-glucans, on the cell wall of target cells and are translocated to secondary receptors on the plasma membrane causing osmotic lysis and resulting in cell death [15]
The yeast W. anomalous produces several KTs, each characterized by variable molecular weights, a large range of optimal pH and temperature and a wide antimicrobial activity against several microorganisms [16,17]
Summary
Killer yeasts can secrete one or several kinds of toxins with peculiar molecular weights and post-translational modifications, which are able to kill sensitive cells of the same or related yeast genera in the absence of a direct cell-cell contact [1]. Killer toxin producers are immune to their own toxin but they can be susceptible to the toxins secreted by other killer yeasts [2]. These toxins act by targeting cell wall receptors of the sensitive cells with the killing mechanism consisting of a strong β-1,3-glucanase activity [3,4]. The Wickerhamomyces anomalus is a Saccharomyces yeast with a wide spectrum of antimicrobial activities commonly used in food bio-preservation [7]. This yeast is observed in different habitats
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