RcsAB and Fur Coregulate the Iron-Acquisition System via entC in Klebsiella pneumoniae NTUH-K2044 in Response to Iron Availability

Abstract

The iron acquisition system is an essential virulence factor for human infection and is under tight regulatory control in a variety of pathogens. Ferric-uptake regulator (Fur) is one of Fe²⁺-responsive transcription factor that maintains iron homeostasis, and the regulator of capsule synthesis (Rcs) is known to regulate exopolysaccharide biosynthesis. We speculate the Rcs may involve in iron-acquisition given the identified regulator box in the upstream of <i>entC</i> that participated in the biosynthesis of enterobactin. To study the coregulation by RcsAB and Fur of <i>entC</i>, we measured the β-galactosidase activity and relative mRNA expression of <i>entC</i> in WT and mutant strains. The RcsAB- and Fur-protected regions were identified by an electrophoretic mobility shift assay (EMSA) and a DNase I footprinting assay. A regulatory cascade was identified with which Fur repressed <i>rcsA</i> expression and reduced RcsAB and <i>entC</i> expression. Our study demonstrated that <i>entC</i> was coregulated by two different transcriptional regulators, namely, RcsAB and Fur, in response to iron availability in <i>Klebsiella pneumoniae</i>.