The cell-associated magnesium content is affected in Salmonella mutants defective for SigmaS/RpoS and O-antigen synthesis

In many Gram-negative bacteria, the stress sigma factor of RNA polymerase, σS/RpoS, remodels global gene expression to reshape the physiology of quiescent cells and ensure their survival under non-optimal growth conditions. In the foodborne pathogen Salmonella enterica serovar Typhimurium, σS is also required for biofilm formation and virulence. Our recent work has shown that a ΔrpoS mutation reduces the magnesium content of Salmonella (Metaane et al. 2022, PLoS ONE 17(3): e0265511). The O-antigen of LPS is a Mg2+ reservoir that can be used under magnesium deprivation. We show here that eventhough the cell-associated magnesium content is affected when Salmonella lacks the entire O-antigen, an effect of the ΔrpoS mutation can be still observed. We have also shown that the amount of intracellular free Mg2+ is slightly reduced in the ΔrpoS mutant compared to the wild-type strain (Metaane et al 2023, PLoS ONE 18(9): e0291736). This work was supported by the French National Research Agency (ANR-19-CE44-0005-01, PERIOMET project).