Uptake of iron from ferric-citrate in the cyanobacteria Synechocystis PCC6803.

Iron is an essential element for bacterial growth. Its intracellular concentration is mainly controlled at the uptake level, which is mediated by iron-dicitrate transport in various prokaryotes. We report here that the cyanobacterium Synechocystis PCC6803 takes up iron from ferric citrate. This process is dependent of the iron:citrate ratio, with a better efficiency for the highest concentration of citrate. The iron-citrate complex is the substrate of this active uptake, inhibited in part by the uncoupler FCCP. Iron starvation activates this uptake. These data suggest the existence of a specific ferric citrate receptor on the cyanobacterial membrane.