Journal of Pure and Applied MicrobiologyVol. 3 No. 2

Possible Involvement of Plasmids in the Expression of Killer Toxins of Saccharomyces cerevisiae

Sahar A. Alshalchi¹*, Sijal W. Alrikabi² and Ahmad Sahi²

¹Department of Biotechnology, College of Science, Baghdad University, Baghdad, Iraq. ²Department of Biology, College of Science, Almustansiriya University, Baghdad, Iraq.

Received on 05 June 2009 and accepted on 12 July 2009



Four isolates of Saccharomyces cerevisiae were selected in this study for their high ability to produce killer toxin, to investigate possible correlation between their plasmids contents and killer activity. Plasmid's profiles on agarose gel revealed presence of two plasmids in each of four isolates. Yeast cells obtained after plasmid curing experiments at elevated temperature showed that cured isolates lost their killing capacity. The plasmid cured yeast cells originated from three yeast isolates (Scs7, Scvi8 and Scf14 ) showed the possible correlation between plasmid curing and loss of killing ability, whereas isolate Scf4 retained the killing ability in absence of plasmids. Moreover, the extracted plasmid samples were shown to be sensitive to RNase treatment. These results might suggest that the genetic determinants for toxin production in three isolates (Scs7, Scvi8 and Scf14 ) of selected killer's yeasts of S. cerevisiae are encoded by dsRNA plasmid(s) except one isolate (Scf4), in this isolate the killer protein may be mediated by chromosome.

Keywords : Saccharomyces cerevisiae, Killer toxins, Plasmids.