Iron uptake processes in Mycobacterium vaccae R877R, a mycobacterium lacking mycobactin

The production of exochelins (MV) was established in Mycobacterium vaccae R877R under iron-deficient conditions in concentrations about five times greater than in Mycobacterium smegmatis. M. vaccae does not produce mycobactin nor is salicylic acid secreted into the medium. A simple method is described using 55Fe-labelled culture filtrates for assessing exochelin production and which would be applicable to other mycobacteria. One of the exochelins produced (MV3) is part of an active iron uptake system and another (MV1) is responsible for a passive uptake system. MV3 exochelin has similar chromatographic properties and biological activity to the major exochelin produced by M. smegmatis: iron uptake from MV3 exochelin was inhibited by dinitrophenol, NaN3 and HgCl2, and was judged to be an active transport process. This process was not inhibited by equimolar amounts of ferri-salicylate or ferri-citrate both of which could be used separately as sources of iron for the organism. Uptake from these latter sources was insensitive to metabolic inhibitors and uncouplers. The multiplicity of pathways for iron uptake in a single organism is discussed.