Pat- and Pta-mediated protein acetylation is required for horizontally-acquired virulence gene expression in Salmonella Typhimurium.

Salmonella Typhimurium is a Gram-negative facultative pathogen that causes a range of diseases, from mild gastroenteritis to severe systemic infection in a variety of animal hosts. S. Typhimurium regulates virulence gene expression by a silencing mechanism using nucleoid-associated proteins such as Histone-like Nucleoid Structuring protein (H-NS) silencing. We hypothesize that the posttranslational modification, specifically protein acetylation, of proteins in gene silencing systems could affect the pathogenic gene expression of S. Typhimurium. Therefore, we created acetylation-deficient mutant by deleting two genes, pat and pta, which are involved in the protein acetylation pathway. We observed that the pat and pta deletion attenuates mouse virulence and also decreases Salmonella's replication within macrophages. In addition, the Δpat Δpta strain showed a decreased expression of the horizontally-acquired virulence genes, mgtC, pagC, and ugtL, which are highly expressed in low Mg2+. The decreased virulence gene expression is possibly due to higher H-NS occupancy to those promoters because the pat and pta deletion increases H-NS occupancy whereas the same mutation decreases occupancy of RNA polymerase. Our results suggest that Pat- and Pta-mediated protein acetylation system promotes the expression of virulence genes by regulating the binding affinity of H-NS in S. Typhimurium.