Global Effects of the Transcriptional Regulators ArcA and FNR in Anaerobically Grown Salmonella enterica sv. Typhimurium 14028s.

Abstract

EVANS, MATTHEW RICHARD. Global Effects of the Transcriptional Regulators ArcA and FNR in Anaerobically Grown Salmonella enterica sv. Typhimurium 14028s. (Under the direction of Dr. Hosni M. Hassan.)

The purpose of this research was to assess and compare the genome-wide transcriptional profiles and virulence in mice of the global regulators, FNR (Fumarate Nitrate Reductase) and ArcA (Aerobic Respiratory Control) in anaerobically grown Salmonella enterica serovar Typhimurium 14028s. FNR controls the expression of target genes by sensing and responding to the presence or absence of dioxygen via assembly-disassembly of oxygen-liable iron-sulfur clusters, while ArcA is a two-component (ArcA/ArcB), cytosolic redox response regulator. This work demonstrates that FNR is a positive regulator of motility, flagellar biosynthesis, and pathogenesis. An fnr mutant was non-motile, lacked flagella, attenuated for virulence in mice, and did not survive inside macrophages. In S. Typhimurium, as in Escherichia coli, the FNR modulon encompassed the core metabolic and energy functions as well as motility. Salmonella-specific genes/operons regulated by FNR included those required for ethanolamine utilization, newly identified flagellar genes (mcpAC, cheV), several virulence genes in Salmonella pathogenicity island 1 (SPI-1), and the srfABC operon. ArcA serves as a transcriptional repressor/activator coordinating cellular metabolism and motility. An arcA mutant was non-motile, lacked flagella, and was as virulent as the wild-type strain via intraperitoneal challenge in mice. In S. Typhimurium, as in E. coli, the ArcA modulon encompassed the core metabolic and energy functions as well as motility. Salmonella-specific genes/operons regulated by ArcA included those for propanediol utilization, newly identified flagellar genes (mcpAC, cheV), Gifsy-1 prophage genes, and a few virulence genes located in SPI-3 (mgtBC, slsA, STM3784). Regulation by either ArcA or FNR in S. Typhimurium is similar, but distinct from that in E. coli. Genes/operons involved in the succinyl-CoA pathway, fatty acid degradation, flagellar biosynthesis, motility, chemotaxis, cytochrome oxidase complexes are regulated similarly in the two organisms by ArcA. Genes/operons involved in aerobic metabolism, NO• detoxification, flagellar biosynthesis, motility and chemotaxis, and anaerobic carbon utilization are regulated similarly in the two organisms by FNR. Herein, we present the first report on the global role of these two redox regulators in S. Typhimurium. According this study, we hypothesize that FNR plays a more heirarchical role than ArcA in pathogenesis and during the transition between aero- and anaerobiosis in the host. Furthermore, when comparing the motility and virulence results from our work on FNR to those on ArcA, we show that the lack of motility does not necessarily correspond to the lack of virulence in S. Typhimurium.