Active Transport of Iron in Bacillus megaterium: Role of Secondary Hydroxamic Acids

Abstract

Kinetics of radioactive iron transport were examined in three strains of Bacillus megaterium . In strain ATCC 19213, which secretes the ferric-chelating secondary hydroxamic acid schizokinen, 59 Fe 3+ uptake from 59 FeCl 3 or the ferric hydroxamate Desferal- 59 Fe 3+ was rapid and reached saturation within 3 min. In strain SK11, which does not secrete schizokinen, transport from 59 FeCl 3 was markedly reduced; the two ferric hydroxamates Desferal- 59 Fe 3+ or schizokinen- 59 Fe 3+ increased both total 59 Fe 3+ uptake and the 59 Fe 3+ appearing in a cellular trichloroacetic acid-insoluble fraction, although 10 min was required to reach saturation. Certain characteristics of transport from both ferric hydroxamates and FeCl 3 suggest that iron uptake was an active process. The growth-inhibitory effect of aluminum on strain SK11 was probably due to the formation of nonutilizable iron-aluminum complexes which blocked uptake from 59 FeCl 3 . Desferal or schizokinen prevented this blockage. A strain (ARD-1) resistant to the ferric hydroxamate antibiotic A22765 was isolated from strain SK11. Strain ARD-1 failed to grow with Desferal-Fe 3+ as an iron source, and it was unable to incorporate 59 Fe 3+ from this source. Growth and iron uptake in strain ARD-1 were similar to strain SK11 with schizokinen-Fe 3+ or the iron salt as sources. It is suggested that the ferric hydroxamates, or the iron they chelate, may be transported by a special system which might be selective for certain ferric hydroxamates. Strain ARD-1 may be unable to recognize both the antibiotic A22765 and the structurally similar chelate Desferal-Fe 3+ , while retaining its capacity to utilize schizokinen-Fe 3+ .