Transcriptomic Responses of Kveik Yeasts to Heat and Ethanol Stress

Kveik strains are a group of Saccharomyces cerevisiae strains notable for their exceptional tolerance to environmental stress. To investigate the molecular basis of this robustness, the transcriptomes of three kveik strains and a conventional ale strain were compared under non-stress and stress conditions using RNA-seq. Under non-stress conditions, kveik strains showed elevated basal expression of environmental stress response genes, suggesting that part of the stress-responsive transcriptional program is active irrespective of stress exposure. Catalase activity was elevated, providing physiological support for the transcriptomic findings related to oxidative-stress defense. Under sublethal heat stress, conventional ale yeast displayed transcriptional patterns associated with cell-cycle restraint and chromosome organization, whereas kveik strains showed enrichment of genes related to protein refolding, ribosome biogenesis, and cell-wall biosynthesis, suggesting retention of a transcriptional emphasis on growth-associated processes alongside stress-protective responses. Under ethanol stress, both groups upregulated translation-related processes; however, metabolic functions were more strongly enriched in ale yeast, while kveik strains showed patterns consistent with maintenance of translation-related functions together with increased emphasis on cell surface-associated processes. Overall, kveik stress tolerance appears to reflect elevated basal preparedness and transcriptional patterns consistent with the maintenance of biosynthetic and structural processes under stress, supporting their potential suitability for intensive industrial fermentations.