Saccharomyces Cerevisiae
The best characterized toxin system is from yeast (Saccharomyces cerevisiae), which was found to spoil brewing of beer. In S. cerevisiae are toxins encoded by a double-stranded RNA virus, transcribed as a precursor, cleaved and secreted outside of the cells, where they may affect susceptible yeast. There are other killer systems in S. cerevisiae, such as KHR and KHS genes encoded on chromosome.
Read more about this topic: Killer Yeast