The ability of a sideroPhore-catabolizing bacterium to assimilate ferr
ic ion was examined. While the bacterium utilizes the siderophore defe
rrioxamine B (DFB) as a carbon source, it was incapable of using the f
erric ion analogue (ferrioxamine B) as an iron source. It did, however
, assimilate the ferric ion of the chelator ferric nitrilotriacetic ac
id and of the siderophore ferrirhodotorulic acid (ferriRA). Neither fe
rriRA nor its deferrated analog (RA), however, were capable of functio
ning as carbon sources for the bacterium. The microbe thus employs a '
nutritional selectivity' with respect to these two siderophores. That
is, it does not use the siderophore it employs as a carbon source (DFB
) as an iron source nor does the siderophore utilized as an iron sourc
e, i.e. ferriRA, nor its deferrated analog (RA), serve as carbon sourc
es for the organism.