Iron Differentially Regulates Gene Expression and Extracellular Secretion ofVibrio vulnificusCytolysin‐Hemolysin

In a previous study, we showed that Vibrio vulnificus is a ferrophilic bacterium that requires high levels of available iron for growth. In the present study, we show that iron stimulates, in an unusual manner, the production of cytolysin-hemolysin (VvhA), the most potent exotoxin produced by V. vulnificus. The vvhA gene possesses a putative ferric uptake regulator (Fur)-binding box in the regulatory region, andvvhA transcription was repressed by iron and de-repressed by fur mutation. However, extracellular secretion of VvhA was conversely increased by iron. Iron increased transcription of pilD, which encodes PilD, a component of the type II general secretion system responsible for extracellular VvhA secretion. These results indicate that iron increases extracellular VvhA secretion via the type II general secretion system, although it can repress vvhA transcription via Fur.