The small RNA RyhB contributes to siderophore production and virulence of uropathogenic Escherichia coli

Abstract

In Escherichia coli, the small regulatory noncoding RNA (sRNA) RyhB and the global ferric uptake regulator (Fur) mediate iron acquisition and storage control. Iron is both essential and potentially toxic for most living organisms, making the precise maintenance of iron homeostasis necessary for survival. While the roles of these regulators in iron homeostasis have been well studied in a nonpathogenic E. coli strain, their impact on the production of virulence-associated factors is still unknown for a pathogenic E. coli strain. We thus investigated the roles of RyhB and Fur in iron homeostasis and virulence of the uropathogenic E. coli (UPEC) strain CFT073. In a murine model of urinary tract infection (UTI), deletion of fur alone did not attenuate virulence, whereas a ΔryhB mutant and a Δfur ΔryhB double mutant showed significantly reduced bladder colonization. The Δfur mutant was more sensitive to oxidative stress and produced more of the siderophores enterobactin, salmochelins, and aerobactin than the wild-type strain. In contrast, while RyhB was not implicated in oxidative stress resistance, the ΔryhB mutant produced lower levels of siderophores. This decrease was correlated with the downregulation of shiA (encoding a transporter of shikimate, a precursor of enterobactin and salmochelin biosynthesis) and iucD (involved in aerobactin biosynthesis) in this mutant grown in minimal medium or in human urine. iucD was also downregulated in bladders infected with the ΔryhB mutant compared to those infected with the wild-type strain. Our results thus demonstrate that the sRNA RyhB is involved in production of iron acquisition systems and colonization of the urinary tract by pathogenic E. coli.