SanA is an inner membrane protein mediating <i>Salmonella</i> Typhimurium infection

Bacterial membrane proteins like SanA are essential for environmental interactions, significantly affecting the physicochemical properties of the bacterial envelope and influencing <i>Salmonella</i>'s antibiotic resistance and infection traits. Previous research links <i>sanA</i> deletion to increased <i>Salmonella</i> invasiveness, though the mechanisms are poorly understood. This study explores SanA's role in <i>Salmonella</i> infection both <i>in vitro</i> and <i>in vivo</i>. It examines its expression pattern, subcellular localization, and connection with the genetic background responsible for the infection phenotype following <i>sanA</i> knockout. Through subcellular fractionation and Western blotting, SanA was found mainly in the inner membrane. Transcriptional fusion indicated that <i>sanA</i> expression is important during late exponential and early stationary growth phases and remains significant 24 h post-host cell entry. Invasion assays showed that <i>sanA</i> deletion in bacteria grown to early stationary phase increased invasiveness, partly due to higher <i>sicA</i> expression regulated by nutrient availability. <i>In vivo</i> results supported these findings, with the <i>sanA</i> mutant exhibiting enhanced colonization of mouse organs but being outcompeted by the wild type in competitive infection. This study provides new insights into the role of SanA in <i>Salmonella</i>'s response to environmental stress, including hostile environments, emphasizing the importance of inner membrane proteins in shaping bacterial fitness and pathogenicity.IMPORTANCE<i>Salmonella</i> poses significant global health and economic challenges. Its successful infection depends on complex interactions between the bacteria and host cells, involving various proteins in the bacterial envelopes. One such protein, SanA, plays a role in bacterial interaction with the environment, affecting antibiotic resistance and infection capability. Previous studies revealed that removing the <i>sanA</i> gene increases <i>Salmonella</i>'s ability to enter the host cells, though the underlying mechanisms were unclear. This research investigates SanA's role during infections, discovering its primary location in the inner bacterial membrane and its heightened activity during specific growth phases and post-host cell entry. Removing <i>sanA</i> made the bacteria more invasive, likely due to the upregulation of genes aiding host cell infection, especially in nutrient-rich conditions. In mouse infection experiments, SanA-deficient bacteria colonized organs more effectively but were less competitive when wild-type and mutant bacteria coexisted. This indicates SanA's role in managing environmental stress, enhancing <i>Salmonella</i>'s infection and survival capabilities.