Role of the Salmonella enterica serovar Typhi Fur regulator and small RNAs RfrA and RfrB in iron homeostasis and interaction with host cells

Abstract

Iron is an essential element but can be toxic at high concentrations. Therefore, its acquisition and storage require tight control. Salmonella encodes the global regulator Fur (ferric uptake regulator) and the small regulatory non-coding RNAs (sRNAs) RfrA and RfrB, homologues of RyhB. The role of these iron homeostasis regulators was investigated in Salmonella enterica serovar Typhi (S. Typhi). Strains containing either single or combined deletions of these regulators were obtained. The mutants were tested for growth in low and high iron conditions, resistance to oxidative stress, expression and production of siderophores, and during interaction with host cells. The fur mutant showed a growth defect and was sensitive to hydrogen peroxide. The expression of the sRNAs was responsible for these defects. Siderophore expression by S. Typhi and both sRNAs were regulated by iron and by Fur. Fur contributed to invasion of epithelial cells, and was shown for the first time to play a role in phagocytosis and intracellular survival of S. Typhi in human macrophages. The sRNAs RfrA and RfrB were not required for interaction with epithelial cells, but both sRNAs were important for optimal intracellular replication in macrophages. In S. Typhi, Fur is a repressor of both sRNAs, and loss of either RfrA or RfrB resulted in distinct phenotypes, suggesting a non-redundant role for these regulatory RNAs.

The Small RNA RyhB Contributes to Siderophore Production and Virulence of Uropathogenic Escherichia coli

“…They are involved in protection against oxidative stress, bactericidal antibiotic and acid resistance, and survival within epithelial cells and macrophages (7,61). RyhB-2 is also implicated in the regulation of motility in S. Typhimurium, and the highest expression of both sRNAs in S. Typhi was obtained during interaction with host cells, which correlates with their role in virulence (27,62).…”

“…For CFT073, we demonstrated that the ⌬fur mutant was more sensitive to H 2 O 2 than the wild-type parental strain in iron-poor and iron-rich media. Similarly, for S. Typhi, it has been shown that the sRNAs RyhB-1 and RyhB-2 are responsible for sensitivity of the ⌬fur mutant to H 2 O 2 , as enzymes required in response to oxidative stress resistance, such as superoxide dismutases, are repressed by RyhB (5,27). However, for CFT073, the ⌬ryhB ⌬fur double mutant was more sensitive to H 2 O 2 than the ⌬fur mutant in iron-rich medium and iron-poor medium, suggesting that other, unknown mechanisms are involved in the oxidative stress response in this strain.…”

“…also been shown that deregulation of iron homeostasis increases sensitivity to reactive oxygen species, such as H 2 O 2 , in Salmonella enterica serovar Typhi and S. Typhimurium (27,60). Therefore, we determined whether Fur and/or RyhB contributes to H 2 O 2 resistance in UPEC strain CFT073.…”

“…Because several studies on nonpathogenic E. coli and Salmonella enterica previously demonstrated the roles of Fur and RyhB in siderophore production (18,19,27), we determined whether these regulators have an impact on siderophore production in the UPEC strain CFT073. We compared production of the three types of siderophores by strain CFT073 (enterobactin, salmochelins, and aerobactin) directly from supernatants of bacterial cultures grown in iron-poor medium.…”

“…Thus, RyhB plays an essential role in bacteria that require adaptation to iron starvation. Moreover, this sRNA also contributes to many pathogenicity determinants, such as acid resistance in Shigella flexneri (21); eukaryotic cell invasion and cell-to-cell spread in Shigella dysenteriae (22,23); motility, chemotaxis, and biofilm formation in Vibrio cholerae (24,25); biosynthesis of capsular polysaccharide and iron acquisition in Klebsiella pneumoniae (26); and oxidative stress resistance, survival inside human macrophages, and iron acquisition in Salmonella enterica serovar Typhi (27).…”