First Evidence of Metabolically Active Intracellular Bacteria in Saccharomyces cerevisiae

Quorum sensing (QS) is a cell-to-cell signaling system that takes place at a key concentration (quorum) of signal molecules and via a peculiar signaling pathway. Both bacteria and yeasts possess QS mechanisms, mediated by specific molecules (farnesol, tyrosol, 2-phenylethanol, tryptophol) in yeasts, and N-acylhomoserine lactones (AHLs) and modified oligopeptides in bacteria. Here, we report the first chemical evidence of bacterial QS activity in yeast Saccharomyces cerevisiae (OS3 and V5 strains) by UPLC-MS/MS identification of N-octanoyl- and N-decanoyl-L-homoserine lactones in cell-free culture media extracts. The AHLs' presence was unexpected, as they are produced exclusively by bacteria. Tyrosol, a yeast signal molecule, was identified and quantified by NMR analysis. Metataxonomic analysis suggested the existence inside S. cerevisiae cells of bacteria, including Firmicutes, Bacteroidota, and Proteobacteria. Our study paves the way for investigations into bacterial detection within S. cerevisiae cells and their role in biotechnological performance in the food fermentation fields.