Production of aerobactin by microorganisms from a compost enrichment culture and soybean utilization

Fe chelators produced by compost microorganisms in C enrichment culture can efficiently improve Fe nutrition of soybean and oat under slightly alkalin e conditions. Little information is available, however, concerning the iden tity of these chelators. A study was conducted to identify the Fe chelators and the microorganisms responsible for their production and to evaluate th e mechanism of Fe uptake by soybean of these Fe chelates. One Fe chelator p redominated in the culture solution and, after purification using chromatog raphy, it was identified by nuclear magnetic resonance and mass spectrometr y as the siderophore, aerobactin. A strain of Citrobacter diversus, which p roduced a high concentration of aerobactin, was isolated and purified from the culture. Bathophenanthrolinedisulfonic acid (BPDS), an Fe2+ trap, did n ot decrease soybean uptake of Fe of which more than 90% was in the form of an Fe-aerobactin complex. Reduction of Fe as Fe-aerobactin by soybean roots was not detected. Iron uptake was, however, significantly (P similar to 0. 05) inhibited by NaN3, a respiratory inhibitor. These results suggest that the Fe may have been taken up by soybean as an Fe-aerobactin complex throug h an active transport mechanism.