# First Evidence of Metabolically Active Intracellular Bacteria in Saccharomyces cerevisiae

## TL;DR

This study provides the first evidence of bacteria living inside yeast cells and producing bacterial signaling molecules, which could impact food fermentation processes.

## Contribution

The first chemical evidence of bacterial quorum sensing molecules in yeast cells is presented.

## Key findings

- N-octanoyl- and N-decanoyl-L-homoserine lactones were detected in yeast culture media.
- Bacteria such as Firmicutes, Bacteroidota, and Proteobacteria were found inside S. cerevisiae cells.
- Tyrosol, a yeast signaling molecule, was identified and quantified using NMR analysis.

## Abstract

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.