Gas bubble formation in fermenting and non-fermenting yeasts

[摘要] English: Literature previously suggested that intracellular gas bubble formation cannot occur in microorganisms even under high gas supersaturation. This observation was disproved with the discovery of gas bubbles in the yeasts Saccharomyces cerevisiae (baking industry) and Saccharomyces pastorianus (Brewing industry). As a result the missing link between the excessive production of carbon dioxide (CO2) by alcoholic fermentation inside the yeast cells and the vigorous release of this CO2 into the surrounding environment was uncovered. Further investigations proved that CO2 was indeed the gas contained inside these gas bubbles yet additional analysis of this gas composition was still needed.Here we investigate the occurrence of gas bubbles in yeasts that are fermenting and non-fermenting to identify any occurring differences and conserved status of gas bubbles formation in yeasts. Gas bubbles occurring in Crabtree-positive fermenting yeasts were observed to be more than those formed in the other yeasts (Crabtree-negative and strictly respiring yeasts). Although this was observed only on fermentable media, while on non-fermentable media less or no gas bubbles were formed. Furthermore, the Crabtree-negative fermenting and strictly respiring yeasts revealed similar results on both fermentable and non-fermentable media, with little to no gas bubble formation. Gas composition analysis was also carried out on three Crabtree-positive yeasts and it indicated the occurrence of five elements that were expected to be present in our samples. Moreover detection of sulphur compounds was observed in the same three samples with varying intensities. Nonetheless further research is still needed to confirm the point of production for these compounds, using more specific and sensitive techniques. From these findings it can be concluded that gas bubble formation is conserved in yeasts, with the amount of bubbles formed depending on the mode of CO2 production. In addition, it is possible that other gases or compounds such as sulphur compounds can be contained inside these gas bubbles.

[发布机构] University of the Free State