Interaction Mechanism of Wickerhamomyces anomalus and Saccharomyces cerevisiae in Mixed Culture Fermentation

To evaluate the application potential of Wickerhamomyces anomalus (Wa) K-008 in mixed culture fermentation and its interaction mechanism with Saccharomyces cerevisiae (Sc) ZM-005 in co-fermentation, pure and mixed culture fermentations of the two strains were carried out. The biomass, glucose consumption, ethanol production and fermentation rate were measured during the fermentation process. It was found that after 24 hours of mixed culture fermentation, Wa showed growth arrest and cell death, while the growth of Sc was not significantly affected by the presence of Wa. We preliminarily ruled out that the early death phenomenon was due to Wa autolysis or apoptosis. By analyzing the fermentation supernatant as well as evaluating the ethanol tolerance, we found that the death of Wa at the early stage of fermentation was not due to the lack of nutrients or the toxic effect of Sc. The mixed culture fermentations with high concentrations of viable, broken or dead cells of Sc indicated that cell death in Wa at the early stage was due to the high concentration of live Sc cells in the system but not dead or broken Sc cells. Furthermore, to verify the mechanism of action, the Sc and Wa cells were separated by dialysis to avoid contact between each other. It was found that both Sc and Wa could grow normally in the mixed culture system. In summary, the growth arrest and death of Wa at the early stage of mixed culture fermentation may be caused by the high concentration of live Sc cells through a cell-to-cell contact mechanism.