Biology of Killer Yeast and Technological Implications

Abstract

The killer phenomenon has been reported among various genera of yeast. Potential ability of certain yeast (killer yeast) to kill the other yeast (sensitive yeast) was first observed in the strains of Saccharomyces cerevisiae. The killer yeasts secrete extracellular protein toxin that is fatal for the sensitive yeast, and kills the latter. Killer toxin producer yeasts are immune towards their own toxin but can kill the other sensitive yeasts by employing variety of mechanisms like targeting several cellular components viz. cell wall, plasma membrane, tRNA, DNA etc. The genetic information for production of killer toxin (killer phenotype) is generally present as extra-chromosomal genetic elements like dsRNA or linear DNA, or on the chromosome. The protein toxins produced by several killer yeasts have been thoroughly studied after purification and characterization. Killer toxins encoding genes have been cloned, characterized and expressed in heterologous systems. Significance of yeast-derived killer toxins and/or killer yeasts have been implicated in various areas including food fermentations/yeast-based bioprocesses. Yeast killer phenomenon may play a substantive role in stabilizing the ecosystem. Killer toxins of yeast may have potential for application as biopreservatives, biocontrol agents and as new therapeutic molecules especially against multidrug resistant pathogens. For ethanol-based industries like distilleries, breweries, and wineries, killer yeast can be employed as starter industrial yeast cultures to protect against the wild contaminants. Current article presents recent developments on biological and technological implications of killer yeasts.