S-layer is a key element in metabolic response and entry into the stationary phase in Bacillus cereus AH187.

Bacillus cereus is a food-borne Gram-positive pathogen. The emetic reference strain B. cereus AH187 is surrounded by a proteinaceous surface layer (S-layer) that contributes to its physico-chemical surface properties, and promotes its adhesion in response to starvation conditions. The S-layer produced by B. cereus AH187 is composed of two proteins, SL2 and EA1, which are incorporated at different growth stages. Here, we showed that deletion of the genes encoding SL2 and EA1 produced viable cells, but decreased the glucose uptake rate at the start of growth, and induced extensive reorganization of the cellular and exoproteomes upon entry into the stationary phase. As a consequence, stationary cells were less resistant to abiotic stress. Taken together, our data indicate that the S-layer is crucial but comes at a metabolic cost that modulates the stationary phase response. SIGNIFICANCE: The emetic strains of Bacillus cereus are known to cause severe food poisoning, making it crucial to understand the factors contributing to their selective enrichment in foods. Most emetic strains are surrounded by a crystalline S-layer, which is a costly protein structure to produce. In this study, we used high-throughput proteomics to investigate how S-layer synthesis affects the allocation of cellular resources in the emetic B. cereus strain AH187. Our results demonstrate that the synthesis of the S-layer plays a crucial role in the pathogen's ability to thrive under stationary growth phase conditions by modulating the stress response, thereby promoting its lifestyle as an emetic pathogen. We conclude that the synthesis of the S-layer is a critical adaptation for emetic B. cereus to successfully colonize specific niches.