The production of exotoxins with antimicrobial activity on susceptible microorganisms by yeasts is a relatively
common phenomenon. Exotoxins (generally proteins or glycoproteins) that are able to kill susceptible cells belonging
to 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 toxins
have been reported and their genomes were mapped on double-stranded RNA (S. cerevisiae K1, K2, K28,Ustilage
maydis and Hanseniaspora uvarum) , a linear double-stranded DNA plasmid (Kluyveromyces lactis, Pichia acaciae
and Pichia inositovora) or carried on a chromosome (S. cerevisiae KHS, KHR and Williopsis mrakii). During the last
two decades, secreted killer toxins and toxin-producing killer yeasts have found several applications. For instance in
the food and fermentation industries,killer yeasts have been used to combat contaminating wild-type yeasts which
can occur during the production of wine, beer and bread . Killer yeasts have also been used as bio-control agents in
the preservation of foods , in the bio-typing of medically important pathogenic yeasts and yeast-like fungi , in the
development of novel antimycotics for the treatment of human and plant fungal infections, and finally in the field of
recombinant DNA technology