SanA is an inner membrane protein mediating the early stages of Salmonella infection

Bacterial membrane proteins, crucial for the interaction with the environment, encompass various functional molecules such as SanA. SanA is pivotal for the physicochemical properties of the bacterial membrane, influencing Salmonellas antibiotic resistance and infection phenotype. Previous studies identified a link between sanA mutation and increased Salmonella invasiveness, but the mechanisms underlying this phenomenon remain largely unexplored. Therefore, our research investigates SanAs role during Salmonella infection, examining its expression pattern, localization within the cell, and association with Salmonella Pathogenicity Island I (SPI-I). Using subcellular fractionation and Western Blotting we revealed that SanA is predominantly located in the inner membrane. Additionally, we utilized transcriptional fusion to monitor SanA expression under various environmental conditions. We observed that SanA plays a significant role during the late exponential and early stationary growth phase and remains important 24 hours after the bacteria enter host cells. Moreover, our invasion assays demonstrated that deletion of sanA in bacteria grown to early stationary phase significantly enhances their invasiveness, partly due to increased SPI-I expression, which is regulated in a nutrient availability-dependent manner. Our results highlight SanAs essential role in Salmonellas response to environmental stress, critical for its entry and survival in hostile environments. This research underscores the importance of inner membrane proteins in bacterial pathogenicity, particularly in the initial stages of infection.