Disruption of ECM33 in diploid wine yeast EC1118: cell morphology and aggregation and their influence on fermentation performance.

When investigating yeast gene function in relation to fermentation, many screens rely on haploid yeast derivatives. This, however, is not representative of industrial strains, which are typically diploid. One such example is the disruption of ECM33, which was associated with improved fermentation in the haploid wine yeast C911D, but remains uncharacterised in a diploid industrial strain background. We report on the homozygous disruption of ECM33 in Lalvin EC1118 using CRISPR/Cas9. EC1118 ecm33 resulted in a reduction of fermentation duration in a defined medium with limiting and sufficient nitrogen (-20% and -13%, respectively) when shaken. Increased cell size and aggregation, a phenotype previously unidentified in ecm33∆ as haploid yeast tend to aggregate, was also observed. This phenotype led to premature settling thereby the yeast behaving similarly to EC1118 in wine-like semi-static fermentations in a chemically defined medium. Further assessment in semi-static Riesling and Chardonnay fermentations inoculated based on cell number or biomass resulted in no significant difference or significantly slower fermentation duration in comparison the EC1118, nullifying the benefits of this mutation unless agitation is applied. This study draws attention to phenotypes being condition-dependent, highlighting the need to characterise and verify fermentation efficiency mutations in industrial yeast.