Iron transport in Mycobacterium smegmatis: uptake of iron from ferric citrate

In mycobacterial growth medium 40 to 400 μM citrate was required to solubilize 2 μM 55Fe. This solubilized 55Fe was taken up into both iron-deficient and iron-sufficient washed cell suspensions of Mycobacterium smegmatis and Mycobacterium bovis BCG. Although the 55Fe was taken up into the cell, the citrate was not. The uptake system with M. smegmatis was not inhibited by electron transport inhibitors, uncouplers of oxidative phosphorylation, or thiol reagents and was saturable with iron at approximately 35 μM. The system was independent of the iron transport systems already known to exist in M. smegmatis: i.e., the two exochelin routes of assimilation as well as the mycobactin-salicylate system. It was not induced by the presence of 400 μM citrate in the growth medium, nor did the presence of citrate in the medium affect the production of either exochelin or mycobactin