# SanA is an inner membrane protein mediating Salmonella Typhimurium infection

## TL;DR

The SanA protein in Salmonella is an inner membrane protein that influences bacterial invasiveness and environmental stress response.

## Contribution

This study identifies SanA as an inner membrane protein and reveals its role in modulating Salmonella’s infection and stress response mechanisms.

## Key findings

- SanA is localized in the inner membrane and is active during late exponential and early stationary growth phases.
- Deletion of sanA increases bacterial invasiveness, partly due to upregulated sicA expression in nutrient-rich conditions.
- SanA-deficient bacteria colonize mouse organs better but are outcompeted by wild-type bacteria in mixed infections.

## Abstract

Bacterial membrane proteins like SanA are essential for environmental interactions, significantly affecting the physicochemical properties of the bacterial envelope and influencing Salmonella’s antibiotic resistance and infection traits. Previous research links sanA deletion to increased Salmonella invasiveness, though the mechanisms are poorly understood. This study explores SanA’s role in Salmonella infection both in vitro and in vivo. It examines its expression pattern, subcellular localization, and connection with the genetic background responsible for the infection phenotype following sanA knockout. Through subcellular fractionation and Western blotting, SanA was found mainly in the inner membrane. Transcriptional fusion indicated that sanA expression is important during late exponential and early stationary growth phases and remains significant 24 h post-host cell entry. Invasion assays showed that sanA deletion in bacteria grown to early stationary phase increased invasiveness, partly due to higher sicA expression regulated by nutrient availability. In vivo results supported these findings, with the sanA 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 Salmonella’s response to environmental stress, including hostile environments, emphasizing the importance of inner membrane proteins in shaping bacterial fitness and pathogenicity.

Salmonella 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 sanA gene increases Salmonella’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 sanA 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 Salmonella’s infection and survival capabilities.