Characteristics of iron uptake from hydroxamate siderophores byChlorella vulgarisand the correlation between uptake and reduction

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Abstract
Iron uptake by Chlorella vulgaris from ferric‐rhodotorulic acid (Fe(III)‐RA), ferrioximine B (Fe(III)‐DFOB), ferric‐caffeic acid (Fe(III)‐Caf) and ferric‐citrate (Fe(III)‐Cit) was investigated to further describe this uptake and probe the possible link between ferric reduction and iron uptake. Fe‐59 was used to follow iron uptake, and electron paramagnetic resonance (EPR) was used to observe the reduction of ferric iron. Maximal growth occured when excess chelator was used. Iron was taken up in a biphasic manner with a rapid initial rate that after five minutes slowed to a linear rate of uptake. Cyanide decreased the first, rapid rate for Fe(III)‐RA and Fe(III)‐DFOB, while having no apparent effect on the slower rate. This slow rate was sensitive to 10 μM carbonylcyanide m ‐chlorophenylhydrazone (CCCP). Ferric reduction was closely correlated to iron uptake with Fe(III)‐RA and Fe(III)‐DFOB, while the EPR method does not appear to be applicable to Fe(III)‐Cit. CCCP inhibits uptake and reduction for both Fe(III)‐RA and Fe(III)‐DFOB. The data indicate a possible need for energy to both reduce ferric iron and take up iron from these chelates. It remains to be shown whether uptake and reduction are steps in the same mechanism.