The prevalence and diversity of wild African Saccharomyces cerevisiae

• Main Author: Popescu, Justin
• Format: Others
• Language: en
• Published: 2018
• Online Access: https://hdl.handle.net/10539/25638

A dissertation submitted to the Faculty of Science, University of the Witwatersrand, Johannesburg, in fulfilment of the requirements for the degree of Master of Science. Johannesburg, May 2018. === Saccharomyces cerevisiae is the principle fermentative agent used in the production of wine, beer and bread. It is also an extremely well-studied organism and serves as a model system for many fields of research. Although the human-impact on the evolution of the species is notable, the discovery of ancient wild populations in China, in areas untouched by humans, has ignited interest in its use as an ecological and evolutionary model organism. In this study, we collected 300 samples from a variety of geographical and climatic regions in Africa, and through enrichment culturing, isolated 5 strains of S. cerevisiae from 3 bark samples. The isolation rate was 1%, much lower than other studies, and the low prevalence of the species could be attributed to the absence of a major niche. The phylogeny of isolated strains and global populations was constructed using the UTP14 gene. This included 9 wild African S. cerevisiae isolates. The wild African isolates clustered closely with global domesticated isolates and diverged recently in the history of the species. Phenotypic characterisation studies (which included 5 non-Saccharomyces isolates) revealed that maximum growth rates and tolerance to stress varied greatly within and between species, and that isolates did not cluster according to their phylogeny. Volatile metabolite detection by headspace GC-MS showed that most S. cerevisiae isolates were strong fermenters and that wild isolates performed just as well as commercial isolates, indicating that they may have a domestic origin. Further sampling needs to be performed in remote areas of Africa in order to elucidate the natural history of this species. Our results, however, support the hypothesis that Far East Asia is the origin of the species. === LG2018