Yeasts Producing Killer Toxins: An Overview

Abstract

The production of exotoxins with antimicrobial activity on susceptible microorganisms by yeasts is a relativelycommon phenomenon. Exotoxins (generally proteins or glycoproteins) that are able to kill susceptible cells belongingto the same or congeneric species have been defined as killer toxins. Since first discovered in Saccharomyces cerevisiae, killer strains have been isolated from several yeast genera, including Candida, Cryptococcus, Hanseniaspora, Kluyveromyces, Pichia , Torulopsis , Ustilago , Williopsis and Zygosaccharomyces. Many types of killer toxinshave been reported and their genomes were mapped on double-stranded RNA (S. cerevisiae K1, K2, K28,Ustilagemaydis and Hanseniaspora uvarum) , a linear double-stranded DNA plasmid (Kluyveromyces lactis, Pichia acaciaeand Pichia inositovora) or carried on a chromosome (S. cerevisiae KHS, KHR and Williopsis mrakii). During the lasttwo decades, secreted killer toxins and toxin-producing killer yeasts have found several applications. For instance inthe food and fermentation industries,killer yeasts have been used to combat contaminating wild-type yeasts whichcan occur during the production of wine, beer and bread . Killer yeasts have also been used as bio-control agents inthe preservation of foods , in the bio-typing of medically important pathogenic yeasts and yeast-like fungi , in thedevelopment of novel antimycotics for the treatment of human and plant fungal infections, and finally in the field ofrecombinant DNA technology