Ethanol perturbs cell wall and membrane homeostasis in Wickerhamomyces anomalus

Wickerhamomyces anomalus, a flavor-modulating non-Saccharomyces yeast, has garnered significant interest for its remarkable ability to shape wine flavor profiles. However, during fermentation, yeast cells are inevitably exposed to ethanol stress. The specific structural consequences of this stress, particularly its impact on cell wall and membrane homeostasis, remain unclear.

In this study, we investigated the effects of ethanol stress on the cellular integrity of W. anomalus through a physiological analysis focused on the cell wall and membrane. Our results demonstrated that ethanol stress induced significant morphological and ultrastructural alterations, which were primarily attributed to the disruption of cellular homeostasis. Specifically, ethanol stress compromised cell wall integrity, activated the cell wall integrity (CWI) pathway, and increased the intracellular levels of β-glucan and chitin. Furthermore, ethanol stress disrupted membrane homeostasis by remodeling its composition, reducing integrity and fluidity, while increasing permeability and simultaneously enhancing ATPase activity and elevated intracellular K⁺ levels. Fatty acid profiling also demonstrated a decrease in the monounsaturated fatty acid C18:1 and an increase in very long-chain fatty acids (VLCFAs; C22:0 and C24:0) under ethanol challenge. Exogenous supplementation of these fatty acids was shown to enhance the ethanol stress tolerance of W. anomalus.

These findings provide crucial insights into the mechanistic basis of ethanol stress response in W. anomalus and offer a foundation for developing novel strategies to improve its industrial utilization under fermentative stress conditions.