Fur mutants (Mn-r) of Pseudomonas aeruginosa Fe10 (FF13 and FF28) and PAO1 (FPA12) were evaluated for the pattern of deregulation of pyoverdin synthesis in iron-replete medium with Casamino acids [CAM( Fe)] or succinate [SM(Fe)]. With respect to siderophore synthesis, we found in CAM( Fe) medium two Fur phenotypes: FurA (full deregulation, FF13) and FurB (partial deregulation, FF28 and FPA12). Fur mutants compared to parental strains grew with slower specific growth rates on SM(0) and CAM(0) media in a stirred bioreactor. Fur mutants grew in SM(0) with mu about half of that in CAM(0).