MICROBIAL DISSOLUTION OF IRON AND ALUMINUM FROM SOIL MINERALS - EFFICIENCY AND SPECIFICITY OF HYDROXAMATE SIDEROPHORES COMPARED TO ALIPHATIC-ACIDS

Experimental treatments were performed in order to study the dissoluti on of iron and aluminium from different minerals by siderophores and a liphatic acids, either produced by an ectomycorrhizal fungus (biotic c onditions) or of synthetic origin (abiotic conditions). The selected e xperimental minerals choosen were a well cristallized ferric oxide (go ethite), a mica (biotite) and a sulfide (pyrite). Results shows that t he hydroxamate siderophores produced by the fungus are more efficient in the dissolution of the goethite than the aliphatic acids of same or igin. The efficiency of the siderophore to dissolve goethite is confir med in abiotic experiments. For biotite and pyrite, as iron is more av ailable, any siderophore is produced by the fungus and iron is mobiliz ed by the aliphatic acids. In abiotic conditions siderophore is also m ore efficient than the aliphatic acids tested to dissolve iron from bi otite and pyrite. Large amounts of aluminium are also solubilized by t he siderophore from the biotite. The specificity of siderophore is pro ved not to be very strict as this compound is able to dissolve ferric and ferrous iron from different cristallochemical structure, but also aluminium from silicates. But its efficiency in iron dissolution is al ways predominant and much more with ferric oxide mineral.