We suggest the protective role of RyhB against serum killing is due to the activation of CPS biosynthesis. In E. coli, RyhB plays a positive role in control of the intracellular iron concentration via the degradation of nonessential Compound C order iron-using proteins or an increase in siderophore
production [49–51]. In this study, we also found the deletion of ryhB in Δfur decreased this website siderophore production on the CAS plate under iron-limiting condition (Figure 5). Consistent with E. coli , RyhB in K. pneumoniae regulates siderophore production by activating the expression of enterobactin system genes (entC fepA, and fepB). In addition, we found that RyhB may activate iucA and fecA expression. Since sRNA may positively regulate its target mRNAs via an anti-antisense selleck chemical mechanism to disrupt an intrinsic inhibitory structure in the 5′ mRNA region that sequesters the ribosome-binding site and the first translation codon [52, 53], the 5′-untranslated regions of the iuc and fec operons were analysed for sequences complementary to RyhB by prediction with the bioinformatics application RNAhybrid  (http://bibiserv.techfak.uni-bielefeld.de/rnahybrid/submission.html). However, no apparent base pairing was found in the 5′-untranslated region of the iuc or fec operons, suggesting that the activation
of iucA and fecA by RyhB is not a result of direct interaction. Furthermore, RyhB was found to repress the expression of fhuA and sitA in K. pneumoniae. In E. coli,
RyhB represses the expression of fhuA, which also corresponds to our results . A possible paring between RyhB with the adjacent sequence of translational start site of fhuA and sitA was also predicted by the RNAhybrid algorithm. Alignment of the protected residues predicts that RyhB forms a 7 + 4 + 4 bp RNA duplex with the sitA Ketotifen mRNA (Additional file 1: Figure S1), but no apparent base pairing was found between RyhB and fhuA. However, the direct interaction of RyhB with the sitA mRNA remains to be confirmed. In E. coli, RyhB has been shown to repress several genes that are involved in iron-binding, which may increase the intracellular iron concentration, thereby allowing a better usage of iron and more complete Fur repression of these genes [35, 55]. Nevertheless, this possibility in K. pneumoniae needs to be proven by careful experiments. In this study, the coordinated action of Fur and RyhB was found to regulate the expression of the iron acquisition systems for maintaining intracellular iron homeostasis in K. pneumoniae. Conclusions In this study, we provide an initial characterisation of K. pneumoniae RyhB. Our results suggest that RyhB plays an important role in the Fur regulon, which modulates the CPS biosynthesis and iron acquisition systems in K. pneumoniae, both of which contribute to the infectivity and survival of the bacterium.