Iron Transport Agent Research Articles

Enhanced plant growth by siderophores produced by plant growth-promoting rhizobacteria

Specific strains of the Pseudomonas fluorescens-putida group have recently been used as seed inoculants on crop plants to promote growth and increase yields. These pseudomonads, termed plant growth-promoting rhizobacteria (PGPR), rapidly colonize plant roots of potato, sugar beet and radish, and cause statistically significant yield increases up to 144% in field tests1–5. These results prompted us to investigate the mechanism by which plant growth was enhanced. A previous study indicated that PGPR increase plant growth by antagonism to potentially deleterious rhizoplane fungi and bacteria, but the nature of this antagonism was not determined6. We now present evidence that PGPR exert their plant growth-promoting activity by depriving native microflora of iron. PGPR produce extracellular siderophores (microbial iron transport agents)7 which efficiently complex environmental iron, making it less available to certain native microflora.

Thujaplicins from Thuja plicata as iron transport agents for Salmonella typhimurium.

Strains of Salmonella typhimurium which are unable to synthesize their normal iron transport agent, enterobactin, and which must be supported with an exogenous chelator (siderophore) on certain media, were used to examine various types of wood for the presence of chelators. Western red cedar wood, Thuja plicata, was observed to contain large amounts of three substances that in low concentration would serve as chelators for S. typhimurium. The chelators from T. plicata were characterized and found to be alpha-, beta-, and gamma-thujaplicin. Other planar cyclic alpha-hydroxyketones were examined, and several were found to function as chelators for S. typhimurium.

Antibiotic action of N-methylthioformohydroxamate metal complexes.

The antibiotic activity of metal complexes of N-methylthioformohydroxamic acid against gram-negative Escherichia coli NIHJ and gram-positive Staphylococcus aureus 209P was investigated. The kinetically labile, square-planar, divalent (Cu, Ni, and Pd) and octahedral, trivalent (Fe, Co, and Cr) complexes displayed activity, whereas the more inert platinum(II) or rhodium(III) complex displayed no activity, or activity only at elevated concentrations. The free ligand did not suppress the growth of the above organisms, and the sulfur atom of the ligand in its metal complexes appears crucial for activity. Uptake studies of radioactively labeled N-methylthioformohydroxamic acid, its nickel(II), platinum(II), iron(III), and rhodium(III) complexes were conducted in the Escherichia coli K-12 RW193 mutant, which is defective in the production of its native iron(III) transport agent, enterobactin. Uptake of (55)Fe or (63)Ni label from their metal complexes appeared to occur as free inorganic metal ions. The antibiotic activity of the iron(III) and nickel(II) complexes was not due merely to an enhanced accumulation of metal ions by the cell. Metal complexes of [(35)S]N-methylthioformohydroxamic acid enhanced the accumulation of (35)S label compared to that of the free ligand. The antibiotic activity and uptake data are discussed in terms of possible modes of action.

Synthesis and characterization of iron complexes of rhodotorulic acid: a novel dihydroxamate siderophore and potential chelating drug

The iron complex of rhodotorulic acid (RA) at neutral pH has been found to be dimeric with the formulation Fe2(RA)3, where both iron atoms have the Δ-cis configuration; it is this dimeric complex that functions as an iron transport agent in yeast.

Effect of chelators on the suitability of natural waters for hydrilla growth

The role of chelators in affecting the suitability of natural water for growth of a submersed nuisance aquatic plant, Hydrilla verticillata, has been investigated. Screening studies were done using four synthetic chelators [ethylenedinitrilotetraacetic acid, disodium salt, Na 2 EDTA·2H 2O; ethyleneglycolbis (aminoethyl) tetraacetic acid, EGTA; 1,2-diaminocyclohexanetetra-acetic acid, disodium salt, Na 2CDTA; ethylenediamine- N, N′-diacetic acid, EDDA] and naturally occurring chelators, as a peat extract and as a water sample from Lake Starvation. Analyses included dissolved oxygen and inorganic and organic carbon measurements, as well as nutrient concentrations (calcium, magnesium). The growth characteristic, defined as the per cent dissolved oxygen increase in the presence of hydrilla, was found to be associated with the amount of iron present. For EDTA and CDTA, this quantity also showed a positive relationship with k o 2, the first pseudo first-order rate constant for oxygen production, as expected. This was not seen in the case of EGTA, and this anomaly is attributed to the stable chelation of calcium by EGTA. The availability of calcium ion and, therefore also, the availability of inorganic carbon with which calcium is known to form ion-pair complexes, play a role in making a medium suitable for hydrilla growth. The behavior of natural chelators is complicated, but they could act as iron-transport agents or as calcium-sequestering agents, and their presence in a lake may alter the suitability of the lake for hydrilla growth. The limitations and significance of these points with reference to potential control of hydrilla, are presented and discussed.

Nalpha-acetylfusarinines: isolation, characterization, and properties.

The isolation, purification, and structural elucidation of a new group of naturally occurring hydroxamic acids are described. These compounds are produced by an unidentified species of Penicillium when grown on iron deficient medium. They are closely related structurally to the fusarinines, whose basic structure contains Ndelta-(cis-5-hydroxy-3-methylpent-2-enoyl)-Ndelta-hydroxy-L-ornithine, but the alpha-amino groups in the new compounds are protected by Nalpha acetyl groups. The most complex of the compounds is N,N',N"-triacetylfusarinine C, or N,N'N"-triacetylfusigen, a cyclic triester composed of three molecules on Nalpha-acetylfusarinine. The trimer has growth factor activity for Arthrobacter JG-9 about equal to fusarinine C itself. The monohydroxamate, Nalpha-acetylfusarinine, is more active than the trimer. The greater chemical stability of these compounds compared to the unacetylated fusarinines reconciles the utilization of otherwise unstable amino acid esters as iron transport agents.

Ferrioxamine Iron in Rabbit Reticulocyte Heme Synthesis

Abstract Ferrioxamine B, a naturally occurring sideramine, serves as an iron transport agent and iron donor for heme synthesis in micro organisms. It is unable to effectively replace transferrin in iron delivery for rabbit reticulocyte hemoglobin formation.

Production by Salmonella typhimurium of 2,3-dihydroxybenzoylserine, and its stimulation of growth in human serum.

Transferrin, an iron-binding protein in the sera and tissue fluids of vertebrates, functions primarily as an iron-transport agent [1], but it also may serve as a component of nonspecific defense mechanisms against microbial infection [2, 3]. In normal adult human serum the transferrin is only onethird saturated with iron, and no free iron can be detected by colorimetric methods [4]. To grow in body fluids an organism may, therefore, possess a mechanism for utilizing some of the iron in transferrin.