Regulatory Role of fnr Gene in Growth and tolA Gene Expression in Salmonella Typhimurium

Background: Salmonella Typhimurium (S.Typhimurium) adapts to the broad fluctuations of oxygen concentrations encountered in the host. The transition from aerobic to microaerobic/anaerobic condition encountered in the intestine is mainly regulated by fumarate and nitrate reductase (fnr) regulatory gene and aerobic respiratory control A (arcA) gene. Aim is to appraise the role of fnr gene under anaerobic conditions. Methods: In this study, we deleted fnr gene from S.Typhimurium using lambda red-recombinase mediated gene knockout protocol. Further carried out in vitro characterization and analyzed the differential protein expression in wild type (WT) and isogenic Δfnr null mutant (Δfnr) using SDS-PAGE and MALDI-TOF mass spectrometry under anaerobic conditions. Result: In growth competition, WT strain outcompeted the Δfnr and biofilm-forming ability of Δfnr was significantly reduced compared to WT strain. Swimming motility was reduced in Δfnr strain. Besides, differential protein expression revealed the global changes in the expression of many proteins in fnr strain. One differentially expressed protein was identified as TolA, an inner membrane envelope protein. It points out that fnr may regulate the genes responsible for motility and biofilm formation. FNR protein positively regulates TolA, which is important for bacterial virulence, maintenance of membrane integrity, LPS production and replication of bacteria.