Global transcriptome analysis revealsSalmonellaTyphimurium employs the nitrate-dependent anaerobic pathway to combat bile stress

Abstract

Salmonella Typhimurium is an enteric pathogen that is highly tolerant to bile. Next-generation mRNA sequencing was performed to analyse the stress and adaptive responses of S. Typhimurium to bile. We identified the cellular pathways affected during bile stress in wild type (WT) and a mutant lacking cspE (ΔcspE), which plays an essential role in protection from bile stress. We observed transcriptional upregulation of several genes involved in nitrate metabolism, in response to bile stress. These genes were also differentially expressed between the bile-resilient WT and the bile-sensitive ΔcspE strain. To understand the role of nitrate metabolism in bile stress response, we generated a strain lacking fnr (Δfnr), which is the global regulator of nitrate metabolism in S. Typhimurium. fnr was highly induced in the bile treated WT strain but not in the ΔcspE strain. Notably, the Δfnr strain was susceptible to bile-mediated killing. Our studies revealed a new role for fnr in mediating the bile stress response. In addition, a strain lacking arcA (ΔarcA), a two-component system response regulator involved in anaerobic metabolism, also showed a marked reduction in growth in presence of bile. This corroborated the significance of anaerobic metabolism in S. Typhimurium bile tolerance. Importantly, overexpression of fnr and arcA lowered reactive oxygen species and significantly enhanced the survival of the bile-sensitive ΔcspE strain. We also observed that S. Typhimurium pre-treated with nitrate displayed better growth in the presence of bile. Together, these results demonstrate that nitrate-dependent anaerobic metabolism promotes adaptation of S. Typhimurium to bile.

Role of narL gene in the pathogenesis of Salmonella Typhimurium

“…motility in Pseudomonas [25], biofilm formation in E. coli [27], and Burkholderia pseudomallei [28]. The role of narL has been particularly mentioned in STM for combatting bile stress as well [29]. In the current study, we have addressed that the deletion of narL attenuates several virulence-associated factors like motility, biofilmforming ability, and intracellular survival of STM in vitro which might have led to its competitive exclusion by the wild type strain in vivo in the mouse model.…”

“…Nitrate sensing contributes to virulent parameters, as NarL or its homolog has been regarded to play a central role in regulating motility and biofilm formation in the case of Pseudomonas aeruginosa [25,26], E. coli [27], Burkholderia pseudomallei [28], and so on. Furthermore, Singh et al observed an enrichment in the expression of narL, narG, narH, and narI genes in bile-treated STM inferring the positive impact of nitrate metabolism to combat bile stress in the host [29].…”