Browsing by Author "Oosthuizen, Jennifer Rae"

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    Evolution of mutualistic behaviour between chlorella sorokiniana and saccharomyces cerevisiae within a synthetic environment.
    (Stellenbosch : Stellenbosch University, 2020-12) Oosthuizen, Jennifer Rae; Bauer, Florian; Naidoo-Blassoples, Rene Kathleen; Rossouw, Debra; Stellenbosch University. Faculty of AgriSciences. Dept. of Viticulture and Oenology. Institute for Wine Biotechnology.
    ENGLISH ABSTRACT: Microbial symbioses are abundant in the natural environment. Mutualisms are a subset of these symbioses that still lack fundamental understanding regarding the manner in which these complex interactions form and alter microbial species over time. Phototrophic-heterotrophic microbial systems are becoming more commonplace in research due to the many benefits they can provide when different organisms are combined. Heterotrophic fungal systems are largely utilized in the production of high-value metabolites, while phototrophic microalgal systems are found primarily in the green sector such as carbon dioxide sequestration or biofuel production. Synthetic ecology implemented into thoughtfully designed artificial ecosystems provides an ideal method for both the fundamental study of mutualistic symbioses and the production of improved microbial strains for industry. Both the long- and short-term effects of microbial co-evolution on strain performance are largely unknown. Mutualistic interactions are a way to study these effects as the nature of the interaction, reliance on the survival of a partner species, prevents a single species from outcompeting the other. The clear benefits of mutualistic interactions for industrial applications, such as increased growth of both species and/or the production of novel metabolites, also provide clear incentives to investigate these interactions. This study employed synthetic ecology principles and designed an artificial ecosystem to investigate the effects of co-evolution on a mutualistic yeast-microalgal pairing. The yeast, Saccharomyces cerevisiae, and microalga, Chlorella sorokiniana, were co-evolved in an environment that imposed an obligate mutualism between the two microbial partners for approximately 100 generations. The obligate mutualistic interaction was based upon the reciprocal exchange of carbon (CO2 from S. cerevisiae) and nitrogen (ammonia from C. sorokiniana). Strains were isolated from the 50th and 100th generation for further phenotypic, metabolic and transcriptional analysis compared to the parental strains. Phenotypic screening of isolates took place in both mono- and co-culture (multiple pairwise combinations of evolved yeast and microalgae) with various carbon and nitrogen sources to test the limits and effects of co-evolution. This study clearly demonstrated how even short periods of co-evolution can cause changes to the phenotypic growth and metabolite usage of co-evolved isolates. All co-evolved yeast and microalgal strains showed changes to growth rate and a wide variety of growth patterns when compared to the parental strains. Importantly, changes in the expression of key carbon and nitrogen genes were also observed in the evolved isolates of both species. These observed changes assist in highlighting potential underlying mechanisms that occur during co-evolution. These results, when taken together show that even short periods of co-evolution, can produce strains with different characteristics to the parental strains. Harnessing techniques such as co-evolution in combination with synthetic ecology and artificial ecosystems will allow for the creation of functional ecosystems with applications in a wide variety of sustainable industries such as the bioremediation, carbon capture and biofuel industries.