Comparison of the Abilities of Hydroxamic, Synthetic, and Other Natural Organic Acids to Chelate Iron and Other Ions in Nutrient Solution

Abstract

Chelation modeling was used to predict the abilities of hydroxamate siderophores (HS) and other natural organic acids to chelate Fe and other ions in a modified Hoagland nutrient solution as a function of pH (4.0–10.0). Experimentally determined levels of chelated Fe (pH 5.0–10.0) agreed with our predicted results and with values previously predicted for EDTA (ethylenediaminetetraacetic acid), DTPA (diethylenetriaminepentaacetic acid), and EDDHA [ethylenediamine di(o‐hydroxyphenylacetic) acid].The natural HS, Desferrioxamine B (DFOB), and an unknown mixture of HS isolated from the ectomycorrhizal fungus Boletus edulis, remained fully chelated with Fe at all values of pH. Modeling predicted DFOB to be 99.9% chelated with Fe even in nutrient solution of pH 10.0. No significant chelation of Fe was measured or predicted above pH 6.0 for malate, malonate, oxalate, succinate, α‐ketoglutarate, or pyruvate. Only 4% of citrate was chelated with Fe at pHs 6.0 and 6.4 as determined by direct measurement and computer modeling, respectively.Solubility constants, derived for Fe(OH)3 (amorphous) (amorph.) and FePO4 (amorph.), indicated that FePO4 (amorph.) can control Fe solubility in nutrient solutions of low pH and reduce the ability of ligands to chelate Fe, relative to conditions in which Fe solubility is governed by Fe(OH)3 (amorph.).Since our results indicate that microbially produced hydroxamate siderophores have a significant influence on Fe solubility, we discuss how such ligands could be of importance in the Fe nutrition of plants under natural soil conditions.

EFFECT OF Penicillium bilaji ON THE SOLUBILITY AND UPTAKE OF P AND MICRONUTRIENTS FROM SOIL BY WHEAT

“…The two iron compounds releasing low amounts of ion, i.e., iron pyrite and ferric oxide, in the abiotic solubilization test were the same ones only slightly solubilized by the fungus. Cline et al (1982) Under greenhouse and field conditions, the addition of P. bilaji with or without added rock P resulted in increases in plant dry matter production and P uptake, confirming previously reported work (Kucey 1987;Asea et al 1988). The increase in soil-available P is in line with the observation that P. bilnji is able to solubilize soil P (Asea et al 1987 Raj et al 1981).…”

“…Hartikainen (1981) showed that addition of ethylenediamine tetra-acetic acid (EDTA) to soils could result in increased plant uptake of aluminum, iron and manganese. No study has reported micronutrient solubilization studies utilizing fungal-produced organic acids; however, Cline et al (1982) …”

Isolation and characterization of mineral phosphate-solubilizing bacteria naturally colonizing a limonitic crust in the south-eastern Venezuelan region

“…Moreover, citrate released by Pseudomonas fluorescens has been shown to effectively mobilize P from goethite, a common iron oxide/hydroxide (Hoberg et al, 2005). The carboxylate anions of these organic acids may compete with PO 2À 4 for binding sites and chelate Fe and Al, liberating this way phosphates in solution (Cline et al, 1982;Fox et al, 1990;Gerke, 1992).This could explain the ability of the two strains of Serratia sp. (MMB066 and MMB070) to solubilize FePO 4 , since it has been shown that members of this genera produce both citric and oxalic acids, among other organic acids (Sole´et al, 2000).…”

Organic acid mediated nutrient extraction efficiency in three calcareous soils

“…This is supported by the extraction data showing that citrate extracted much more Ca 2+ than oxalate. Chemical reaction of organic acids with metals depends not only on the chemical reactivity of a given acids (Cline et al 1987), but also on the individual organic acids adsorption/desorption reactions and microbial biodegradation (Jones and Darrah 1994b).…”