Browsing by Author "Petzsch, Irmela"

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    Physical contact in oenological yeast-bacteria interactions
    (2022-03) Petzsch, Irmela; Bauer, Florian
    Yeast-bacteria interactions are of special interest in wine, as these species are responsible for specific fermentative processes and their interactions have downstream effects on the end-product. Typically, these organisms interact through direct (cell-cell) or indirect (metabolic) contact, but limited information is available on the specific mechanisms behind such interactions. Research has focused largely on yeast, thus the role of physical contact in yeast-bacteria interactions remains unclear. One tool to study such interactions is a multi-membrane bioreactor (MMB). This enables the physical separation of cells while maintaining them in the same growth media. This study was designed to optimize a novel MMB to investigate the effect of physical contact in interactions between Saccharomyces cerevisiae yeast and Lactiplantibacillus plantarum bacteria. Additionally, it expands upon previous research where bacterial isolates were exposed to yeast as biotic selection pressures in a directed evolution experiment. Isolates from this experiment were investigated in this study and phenotypes compared to the parental bacteria, to gain insight into evolutionary aspects. The research methodology centred around selecting pairs of strains displaying phenotypes of interest from small-scale yeast-bacteria fermentations, to be further studied in the optimized MMB. Initial small-scale experiments displayed a variety of phenotypes of the evolved bacterial isolates, but most interestingly, some of the evolved isolates displayed an ability to limit yeast growth compared to the parental bacteria strain. These results are aligned with the selection strategy and suggests the success of biotic selection pressures in directed evolution. Based on the data, an isolate of interest, E59, was selected for further investigation in the MMB. Optimizing the MMB entailed performing a variety of experiments to mitigate issues like membrane fouling and ensure cells were successfully filtered. Once the successful growth of both microbial species was achieved over a 24-hour period, yeast and bacteria were investigated in both direct and indirect contact. MMB experiments revealed that physical contact likely plays a significant role in yeast-bacteria interactions. Direct contact improved bacterial growth, while it limited yeast growth compared to indirect contact. This was a major finding from this research. Once again, the effect of directed evolution was highlighted as E59 displayed less fluctuation in its effect on yeast compared to its parent, when contact types were changed. The MMB system was successfully optimized for yeast-bacteria interactions. This research provides relevant insights into both interactions between Lb. plantarum and S. cerevisiae, and the role of physical contact in yeast-bacteria interactions. It also provides a basis for further study of yeast-bacteria interactions in an optimized MMB, with which contact and genetic mechanisms can be investigated.