Search

The article discusses a study which reported that A. hydrophila ATCC 7966 can, under iron-limiting conditions, use xenosiderophore, desferrioxamine B (DFOB) through the regulation of its outer membrane receptor encoded by desA. It further shows the involvement of desR in the transcriptional induction of desA in the presence of DFOB and under iron-limiting conditions. It indicates that microbes producing hydroxamate-type siderophores are widely distributed in aquatic and terrestial environments.

High-affinity iron acquisition in Vibrio parahaemolyticus is mediated by the cognate siderophore vibrioferrin. We have previously reported that the vibrioferrin biosynthesis operon (pvsOp) is regulated at the transcriptional level by the iron-responsive repressor Fur (T. Tanabe, T. Funahashi, H. Nakao, S. Miyoshi, S. Shinoda, and S. Yamamoto, J. Bacteriol. 185:6938-6949,2003). In this study, we identified the Fur-regulated small RNA RyhB and the RNA chaperone Hfq protein as additional regulatory proteins of vibrioferrin biosynthesis. We found that vibrioferrin production was greatly impaired in both the ryhB and hfq deletion mutants, and a TargetRNA search (http://snowwhite.wellesley.edu/targetRNA/index2.html) revealed that the 5'-untranslated region ofpvsOp mRNA (pvsOp 5'-UTR) contains a potential base-pairing region required for the formation of the RyhB-pvsOp 5'-UTR duplex. An electrophoresis mobility shift assay indicated that RyhB can directly bind to thepvsOp 5'-UTR with the aid of Hfq. Rifampin chase experiments indicated that the half-life of pvsOp mRNA in the ryhB and hfq mutants was approximately 3-fold shorter than that in the parental strain, suggesting that both RyhB and Hfq are engaged in the stabilization of pvsOp mRNA. Chrome azurol S assays followed by electrophoresis mobility shift assays and rifampin chase experiments carried out for mutant strains indicated that base pairing between RyhB and thepvsOp 5'-UTR results in an increase in the stability of pvsOp mRNA, thereby leading to the promotion of vibrioferrin production. It is unprecedented that RyhB confers increased stability on a polycistronic mRNA involved in siderophore biosynthesis as a direct target. [ABSTRACT FROM AUTHOR]

The cytotoxicity of Vibrio parahaemolyticus has been related to the type III secretion system 1 effector protein VP1680, which is secreted and translocated into host cells with the help of the specific chaperone protein, VP1682. This study sought to confirm the in silico analysis, which predicted that a small regulatory RNA (Spot 42) could base pair with the region encompassing the ribosomal-binding site and initiation codon of the vp1682 mRNA. Electrophoresis mobility shift assays indicated that Spot 42 could bind to the vp1682 mRNA with the help of Hfq. Consistent with these results, the translation of the vp1682 mRNA was inhibited when both Hfq and Spot 42 were added to the in vitro translation reaction. The cytotoxic activity against infected Caco-2 cells was significantly increased in the Spot 42 deletion mutant (Δspf) at 4 h after infection as compared with the parental strain. Additionally, we observed that both VP1682 and VP1680 were more highly expressed in (Δspf) mutants than in the parental strain. These results indicate that Spot 42 post-transcriptionally regulates the expression of VP1682 in V. parahaemolyticus, which contributes to cytotoxicity in vivo. [ABSTRACT FROM AUTHOR]