Abstract Title

Evolution of Novel Killer Toxins in Saccharomyces cerevisiae

Additional Funding Sources

The project described was supported by the National Institute Of General Medical Sciences of the National Institutes of Health under Award Number P20GM104420.

Abstract

Evolution of Novel Killer Toxins in Saccharomyces cerevisiae

Lance Fredericks and Paul Rowley (mentor)

Killer yeasts produce antifungal toxins in order to reduce the competition with other yeasts in the local environment. These toxins are proteins synthesized from double stranded RNAs (dsRNA) that parasitize a dsRNA totivirus found in the killer yeasts. These toxins could potentially have medical applications because of their potent antifungal activities however they are generally very unstable under physiological conditions, with an optimal activity at pH 4.6.. Our objective is to use evolutionary selection to improve the stability of killer toxins at pH 7. We evolved a killer strain by serial passage in competition with a a susceptible yeast strain. Two competition assays were run simultaneously on pH 4.6 and pH 7 media. We observed that the killer strain evolved at pH 7 lost its ability to kill entirely on pH 7 but maintained a strong killing ability on pH 4.6. We extracted the dsRNA from the evolved strains and observed the presence of dsRNA parasites. There was noticeable shift in size of the dsRNA parasite in the evolved strains. We will compare the sequences of the dsRNA parasite as well as transform the toxin-encoding plasmid into non-killer yeasts to see if the observed phenotype is maintained.

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Evolution of Novel Killer Toxins in Saccharomyces cerevisiae

Evolution of Novel Killer Toxins in Saccharomyces cerevisiae

Lance Fredericks and Paul Rowley (mentor)

Killer yeasts produce antifungal toxins in order to reduce the competition with other yeasts in the local environment. These toxins are proteins synthesized from double stranded RNAs (dsRNA) that parasitize a dsRNA totivirus found in the killer yeasts. These toxins could potentially have medical applications because of their potent antifungal activities however they are generally very unstable under physiological conditions, with an optimal activity at pH 4.6.. Our objective is to use evolutionary selection to improve the stability of killer toxins at pH 7. We evolved a killer strain by serial passage in competition with a a susceptible yeast strain. Two competition assays were run simultaneously on pH 4.6 and pH 7 media. We observed that the killer strain evolved at pH 7 lost its ability to kill entirely on pH 7 but maintained a strong killing ability on pH 4.6. We extracted the dsRNA from the evolved strains and observed the presence of dsRNA parasites. There was noticeable shift in size of the dsRNA parasite in the evolved strains. We will compare the sequences of the dsRNA parasite as well as transform the toxin-encoding plasmid into non-killer yeasts to see if the observed phenotype is maintained.