Impact of direct cell-cell contact on S. cerevisiae in three-species wine yeast consortia
During mixed-species wine fermentations, yeasts actively exchange metabolites and experience direct cell-cell contact, however, the contribution of physical contact in multispecies consortia remains poorly understood. Therefore, this study compared the impact of direct physical cell contact versus indirect (metabolic) contact on Saccharomyces cerevisiae within a three-species consortium, which included Lachancea thermotolerans and Torulaspora delbrueckii, using a novel design of a continuous flow membrane bioreactor. For each condition, growth of fluorescently-labeled yeast strains were monitored by flow cytometry, extracellular metabolites were quantified; and the transcriptional profiles of yeast species were at measured across two sampling points. Direct contact between cells favored S. cerevisiae growth and resulted in faster depletion of certain amino acids (serine, glycine, valine, aspartate, arginine) at the early timepoint. Transcriptomic analysis revealed fewer time-responsive genes under direct contact, but there was significant treatment-specific regulation for this treatment, such as upregulation of high-affinity hexose transporters (e.g. HXT6 and 7) and HPF1 and downregulation of iron-scavenging genes (e.g. FIT2). These results indicate that physical cell-cell contact alters nutrient uptake dynamics and elicits distinct gene expression responses in S. cerevisiae within a multispecies wine consortium, which could impact fermentation ecology and could have implications for aroma formation.