Abstract text (incl. references): Faecalibacterium are among the main bacteria responsible for the consumption of acetate and the production of butyrate, which has anti-inflammatory properties beneficial to intestinal health (1). Yet, little is known about how acetate availability affects this bacterium’s gene expression strategies either in a pure culture or in a complex environnement. Here, we show that, in the early stationary phase, F. duncaniae strain A2-165 can strongly regulate the expression of metabolic, transport and stress-response genes based on acetate availability in a pure culture model. Using RNA-seq, we compared gene expression patterns between two growth phases (late exponential vs. early stationary) and two acetate levels (low: 3 mM vs. high: 23 mM). At low-acetate levels, a general stress response was activated, and protein synthesis expression was down-regulated. At high- acetate levels, there was greater expression of genes related to butyrate synthesis and to the importation of B vitamins and iron. We analyzed a metaproteomic dataset obtained from eight healthy individuals (2), dedicated to the envelope fraction of the gut microbiota. Among the 42 transporter genes upregulated in high-acetate conditions, we found 236 peptides that matched with 10 transporter genes. The second highest degree of protein coverage (43.6%, 51 peptides) was found for the FeoB transporter. Of those 51 peptides, 9 were specific to a single protein in the metaproteomic dataset. Through multiomics and targeted approaches, this work highlights the crucial role that the feoAABC operon might play in iron homeostasis in F. duncaniae strain A2-165’s physiology (3). 1. R. Martin, D. Rios-Covian, E.Huillet, et al.. Faecalibacterium: a genus with expanding potential as a live biotherapeutic product in humans revue soumise à FEMS Microbiol Rev. 2. Henry C, Bassignani A, Berland M, Langella O, Sokol H, Juste C. (2022) Modern Metaproteomics: A Unique Tool to Characterize the Active Microbiome in Health and Diseases, and Pave the Road towards New Biomarkers—Example of Crohn’s Disease and Ulcerative Colitis Flare-Ups. Cells, 8 (11) 1340 3. S. Verstraeten, S. Layec, S. Auger, C. Juste, C.Henry, S. Charif, Y. Jaszczyszyn, H. Sokol, L.Beney, P. Langella, M. Thomas, E. Huillet. Faecalibacterium duncaniae A2-165 regulates the expression of butyrate synthesis, ferrous irouptake, and stress-response genes based on acetate level in early-stationary cultures. https://doi.org/10.21203/rs.3.rs-2481125/v1 preprint en révision