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+).