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Prevention of brown-rot decay by chelators
1992 - IRG/WP 92-1540
In this work the brown-rot decay was shown to be prevented by chelating the endogenous metals existing in wood by using organic or inorganic chelators or iron-binding siderophores. The fungal growth and decaying ability were significantly decreased by the chelating treatments of the solid wood-based culture medium and pine wood pieces, respectively. The transition metals existing in native wood are proposed to be the key elements in the brown-rot decay mechanism. Of these, especially iron has an important role both in the oxidative degradative pathway and for the growth of the decaying organism. This new method may lead to the development of a specific efficient and non-toxic method for preventing brown-rot.
L Viikari, A-C Ritschkoff

The effect of low molecular weight chelators on iron chelation and free radical generation as studied by ESR measurement
2000 - IRG/WP 00-10367
The focus of this work was to improve our current knowledge of the non-enzymatic mechanisms involved in brown-rot decay. Electron Spin Resonance (ESR), also known as Electron Paramagnetic Resonance (EPR), is an attractive technique for the identification and study of chemical species containing unpaired electrons (such as radicals and certain transition metal species). ESR spin-trapping techniques are also commonly used to study very reactive and short-lived free radical species. It has been proposed that low MW chelators as well as Fenton reagents are involved in wood brown-rot decay, at least in early non-enzymatic stages. In this work, the binding between a chelator model compound and ferric iron was studied by ESR spectroscopy. The effects of the chelator model compound, Fenton reagents, as well as the reaction conditions on free radical generation were also studied using ESR spin-trapping techniques. The results indicate: 1. The relative amount of ferric iron bound to chelators is directly related to the chelator / iron ratio in the system. The relative quantity of the chelator-iron complex can be determined by measuring the intensities of the characteristic g4.3 ESR signal. 2. The effects of the chelator/iron ratio, the pH, and other reaction parameters on the hydroxyl radical generation in a Fenton type system could be determined using ESR spin-trapping techniques. 3. Data support the hypothesis that superoxide radicals are involved in the chelator mediated Fenton processes.
Yuhui Qian, B Goodell

Wood degradation mechanisms by the brown rot fungus Gloeophyllum trabeum
1997 - IRG/WP 97-10229
A mechanism for the degradation of wood by the brown rot fungus Gloeophyllum trabeum is outlined. The mechanism includes the function of redox-cycling, low molecular weight phenolic derivatives which sequester and reduce iron in acidic environments. The role of oxalate for the sequestration of iron (hydr)oxides and the pH dependent transfer of iron to the G. trabeum phenolic chelators, as well as for the maintenance of a pH gradient within the cell lumen and wood cell wall is discussed. A hypothesis for the generation of reactive oxygen species from the redox cycling of the phenolate compounds produced by G. trabeum as well as from free phenolics derived from the wood cell wall is outlined. Site specific production of hydroxyl radicals within the wood cell wall is discussed.
B Goodell, J Jellison

Siderophore production by Trichoderma spp. and its importance in the biological control of wood decay fungi
1994 - IRG/WP 94-10070
Competition for iron as well as other micro-nutrients is an essential component of the microbial ecology of many ecosystems. A wide range of micro-organisms including fungi and bacteria have been shown to increase their ability to efficiently capture iron through the production of specialised iron chelating compounds called siderophores. Since iron is in low supply in wood and has been implicated in the wood decay process by basidiomycete fungi, it is likely that any colonising organism which can capture the available iron may well act to biologically control the decay organisms. Many authors have reported that Trichoderma spp. can be used to control basidiomycetes (especially on agar systems) and a number of active mechanisms of antagonism have been identified. These have included competition for nutrients, mycoparasitism, antibiosis and production of volatile antibiotics. Little, however, has been reported on the importance of siderophores in the biological control of wood decay fungi. This paper reports on the ability of Trichoderma isolates to produce both phenolate and hydroxymate type siderophores and examines the potential role of such compounds in the biological control of wood decay fungi by Trichoderma isolates.
U Srinivasan, A Bruce, T L Highley

Preliminary studies of the performance of iron chelators as inhibitors of brown rot (Coniophora puteana) attack
1996 - IRG/WP 96-10185
This paper describes experiments to examine the proposal that the presence of iron is essential for brown rot fungi to utilize hydroxyl radicals remote from the hyphae as a means of converting the wood into a food source. reliminary test results are presented from trials using three different iron chelators impregnated into Scots pine (Pinus sylvestris) sapwood blocks. Their relative effects on the resistance of the blocks to brown rot attack under laboratory mycology trials are detailed. In general, very dilute aqueous solutions of all the chelators studied were capable of inhibiting the attack of brown rot fungus. indications for the application of this branch of basidiomycete control and areas for further study are discussed.
E D Suttie, R J Orsler, P M Wood

The role of oxygen and oxygen radicals in one-electron oxidation reactions mediated by low-molecular weight chelators isolated from Gloeophyllum trabeum.markup
1994 - IRG/WP 94-10086
The KTBA assay for determination of one-electron oxidation activity was used to assay reactions of low-molecular weight chelators isolated from the brown rot fungus Gloeophyllum trabeum. The assay, performed either under air or nitrogen showed that molecular oxygen was an important factor in chelator-mediated oxidation reactions. A reduction in oxidative activity was observed when superoxide dismutase was introduced to the reaction, indicating that superoxide radicals also involved in the reaction and were scavenged by SOD. The KTBA assay showed, similarly to other assays in our laboratory, that the chelators could reduce Fe(III) to Fe(II). However, once chelators were 'oxidized' in this process they appeared to be redox inactive. Preliminary results indicate that chelator redox activity can only be regenerated in the presence of a reductant such as NADH or oxalate.
Jun Lu, B Goodell, Jiang Liu, A Enoki, J Jellison, H Tanaka, F Fekete

The Chelator Mediated Fenton System in the Brown Rot Fungi: Details of the Mechanism, and Reasons Why it has Been Ineffective as a Biomimetic Treatment in some Biomass Applications – a Review
2014 - IRG/WP 14-10828
The chelator-mediated Fenton (CMF) reaction requires the action of two types of chelating compounds. The first chelator, oxalate, solubilizes and then sequesters iron, and the second chelator reduces iron. Iron reduction must be controlled near the fungal hyphae to prevent damaging Fenton chemistry from occurring in that location. Similarly, iron reduction must be promoted within the wood/plant cell wall to promote Fenton chemistry in the proximity of the target lignocellulose. The mechanism for that control is reviewed in this paper. Both neat Fenton and the CMF have been examined by researchers seeking to exploit this relatively simple mechanism for biomass conversion and lignocellulose pretreatment systems. This paper reviews why some of that research has not produced useful depolymerization reactions and why excess amounts of reagents have been required. The application of Fenton treatments requires that the reactive oxygen species produced in the reaction be generated within a nanometer of the target substrate (lignocellulose), and for this to occur in biomass treatments using Fenton or CMF systems, iron must first be allowed to bind to the substrate to allow the reactions to proceed within nanoscale proximity to lignocellulose. Further, excess iron in solution and in interstitial space must be removed as this “free” iron will react preferentially with chelators and peroxide preventing appropriate targeted action on lignocellulose.
B S Goodell, M Nakamura, J Jellison