CHEMICAL-STRUCTURE AND BIOLOGICAL-ACTIVITY OF A SIDEROPHORE PRODUCED BY RHIZOPUS-ARRHIZUS

Rhizopus arrhizus grown on low-Fe medium produces a siderophore, the chemical structure of which was determined by means of H-1 nuclear magnetic resonance (NMR), C-13 NMR, and circular dichroism spectroscopy. The siderophore was identified as N-1,N-4-bis(1-oxo-3-hydroxy-3,4-dicarboxybutyl)-diaminobutane chemically identical to rhizoferrin produced by Rhizopus microsporus. Growth promotion of R. arrhizus by several unferrated chelates in Fe-limited medium was studied in microtitration plates. The impact of rhizoferrin was much more pronounced than the effect of other siderophores. This growth promotion was used as a bioassay for the detection of rhizoferrin. Purified Fe-rhizoferrin was found to be a very efficient Fe source for tomato plants [Lycopersicon lycopersicon (L.) Karsten] in nutrient solutions. Uptake and translocation of Fe-55 mediated by rhizoferrin in a short-term (10-h) experiment were at levels higher than those obtained by other microbial siderophores. Iron-rhizoferrin acted similarly to the synthetic chelate FeEDDHA [ethylenediamine di(o-hydroxyphenylacetic acid)] on remedy of chlorosis in a long-term (14-d) experiment.