Effect of iron limitation on growth, siderophore production, and expression of outer membrane proteins of Vibrio cholerae.

Vibrio cholerae strains secrete a phenolate-type siderophore when grown in low-iron medium. The siderophore was detected as early as 3.5 h after downshift to iron-poor medium, and it continued to accumulate in the medium as the cells entered stationary phase. Two clinical isolates and an environmental isolate were examined for the amount of siderophore produced. The environmental isolate produced more siderophore and continued to secrete it at concentrations of iron that repressed synthesis in the clinical isolates. Concomitant with production of siderophore, at least six new proteins were seen in the outer membranes of iron starved cells. One of the proteins was large (200,000 Mr [220K]) and appeared to be loosely associated with the outer membrane. The other five proteins had approximate Mr values of 77K, 76K, 75K, 73K, and 62K. The 62K protein, like the 40K major outer membrane protein, was heat modifiable. One or more of these proteins may be a component of the receptor for the iron-siderophore complex.