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

Abstract

AbstractSalmonellaTyphimurium is an enteric pathogen that is highly tolerant to bile. Next-generation mRNA sequencing was performed to analyse the stress and adaptive responses ofS. Typhimurium to bile. We identified the cellular pathways affected during bile stress in wild type (WT) and a mutant lackingcspE (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 lackingfnr(Δfnr), which is the global regulator of nitrate metabolism inS. Typhimurium.fnrwas highly induced in the bile treated WT strain but not in the ΔcspE strain. Notably, the Δfnrstrain was susceptible to bile-mediated killing. Our studies revealed a new role forfnrin mediating the bile stress response. In addition, a strain lackingarcA (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 inS. Typhimurium bile tolerance. Importantly, overexpression offnrandarcA lowered reactive oxygen species and significantly enhanced the survival of the bile-sensitive ΔcspE strain. We also observed thatS. Typhimurium pre-treated with nitrate displayed better growth in the presence of bile. Together, these results demonstrate that nitrate-dependent anaerobic metabolism promotes adaptation ofS. Typhimurium to bile.ImportanceSalmonellaTyphimurium, as an enteric pathogen, manifests an extreme example of bile tolerance. This study describes the diverse metabolic changes at the level of transcriptome inS. Typhimurium exposed to bile. We identified the differential expression of several genes involved in anaerobic metabolism between bile-tolerant WT and bile-sensitive ΔcspE strains. Two major regulators of anaerobic metabolism,fnrandarcA, support the growth ofS. Typhimurium in bile. Our results highlight that, in presence of bile,S. Typhimurium activates genes involved in anaerobic metabolism, specifically nitrate metabolism, that improves survival of bacteria during bile stress.