Transcriptomics and functional analysis reveal impaired motility, biofilm formation, invasion and intramacrophage survival of pimt gene-deleted strain of Salmonella Typhimurium.
Inside the host, Salmonella suffers but survives various stresses. Proteins are the prime targets of host inflammatory responses. Salmonella encodes two key protein repair enzymes, methionine sulfoxide reductase (Msr) and protein isoaspartate methyltransferase (PIMT), that reactivates damaged proteins without their translational synthesis. Under stress, the accumulation of L-isoaspartate (isoAsp) residues causes defects in protein shape and function, which lead to impaired bacterial survival. The PIMT converts the isoAsp residues into Asp residues. Earlier, we observed hypersensitivity of Δpimt mutant strain to various stresses and defective colonisation in mice and poultry. Here, we show that Δpimt mutant strain accumulates about 1.67-fold more intracellular ROS levels and higher protein aggregations. RNA-seq analysis of the pimt gene-deleted strain of S. typhimurium revealed differential expression of 2676 genes. Most of the downregulated genes are related to flagellar assembly, chemotaxis, fimbria formation, Salmonella pathogenicity island encoding type-3 secretion system, mainly implicated in motility, adhesion, invasion and intracellular survival inside intestinal epithelium, phagocytic cells, etc. These factors are known to be the major contributors for the virulence of S. typhimurium inside the host. The functional analysis revealed that the Δpimt mutant strain shows defective motility, reduced biofilm formation, and defective invasion and intramacrophage survival. Transcomplementation resulted in partial phenotype (like defective motility, biofilm formation and invasion and intramacrophage survival) restoration of Δpimt mutant strain. Interestingly, supplementation of Δpimt mutant strain culture with reduced glutathione (GSH) resulted in neutralization of ROS and rescued the defective motility and biofilm formation of the mutant strain.