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Potentialities of protein borates as low-toxic, long-term wood preservatives - Preliminary trials
1999 - IRG/WP 99-30212
Boron compounds are efficient wood preservatives, as well as safe for the mammals and environmentally acceptable. Their natural solubility allows them to treat almost any wood species, but is also the cause of their high depletion from treated timber in outside exposure. In order to reduce this leachability, potentialities of proteinic polymer networks retaining boron within the wood have been investigated. Several mixtures of boric acid and proteins (including ovalbumin, collagen, casein, soya flour) have been used to treat pine sapwood miniblocks. The insoluble networks were obtained by protein gelation or coagulation, induced by a physical and/or a chemical factor. These systems appeared to retard boron leaching, the decrease of the leachability rate depending on the protein and the denaturing agent involved in the network creation. The best results have generally been observed for the irreversible heat-induced protein gels. These associations are also able to conserve some boron mobility and activity. Accelerated biological tests of leached wood samples showed good durability performances against Basidiomycetes. The use of protein borates seems to be an interesting basis for low-toxic wood preservatives. Furthermore, in some cases, proteins could add their anti-nutritional factors to boron efficacy to enhance wood protection.
M-F Thévenon, A Pizzi, J P Haluk

The influence of crystalline and amorphous cellulose on extracellular hydrogen peroxide production by brown-rot fungi
1991 - IRG/WP 1482
The production of hydrogen peroxide (H2O2) has been suggested to play a key role in the degradation of wood by wood-rotting fungi. The production of extracellular hydrogen peroxide was studied by a quantitative method which detects the oxidation of the 2,2-azinobis(3-ethylbenzthiazoline-6-sulphonic acid) (ABTS) by H2O2 and horseradish peroxidase (HRP) in liquid culture medium. The carbon sources used were crystalline and amorphous cellulose. Two brown-rotters, Serpula lacrymans and Poria placenta, were able to produce clearly detectable amounts of extracellular hydrogen peroxide in liquid medium which contained crystalline cellulose as carbon source. No detectable H2O2 was produced in conditions where amorphous medium was used as carbon source. This result suggests that the conformational structure of the substrate may induce H2O2 production by brown-rot fungi.
A-C Ritschkoff, L Viikari

Non-enzymatic Gloeophyllum trabeum decay mechanisms: Further study
2001 - IRG/WP 01-10395
Information will be presented on the mechanisms involved in, and potential application of, non-enzymatic wood decay by brown rot decay fungi. Specifically, the hypothesized role of low molecular weight phenolate derivatives will be discussed in relation to non-enzymatic degradation of wood. The mechanism of binding of iron by cellulose, and binding and reduction of iron by fungal derivatives and model compounds is examined. Positive and negative aspects of potential application of these compounds in the generation of free radicals will be discussed.
B Goodell, J Jellison

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

Interaction mechanisms of F/Cr/As/B type preservative and wood
1981 - IRG/WP 3183
The paper reports results of investigations on the fixation of the components of a F/Cr/As/B preservative in wood and its lignin and cellulosic components.
N Ermush, I Andersone

Vapour boron treatment of wood based panels: Mechanism for effect upon impact resistance
1994 - IRG/WP 94-40036
Samples of medium density fibreboard, chipboard and oriented strandboard (OSB) were treated to two retentions of boric acid by a vapour phase treatment. The results of a range of mechanical tests were reported by Hashim et al. (1992, 1993) in which a small reduction in impact resistance was observed. Several investigations were carried out to study how and where this loss in impact resistance occured. Possible mechanisms for the loss in impact resistance are discussed.
R Hashim, R J Murphy, D J Dickinson, J Dinwoodie

Albumin borate: A new non-toxic, wide-spectrum, long-term wood preservative
1998 - IRG/WP 98-30167
Boron, widely recognized for its broad range of activity towards both fungi and insects and for its low mammalian toxicity, can not provide long term protection to treated timber due to its high leachability. Boron, in the form of boric acid, can be partially fixed to timber by the formation of an association with egg albumin, which is insolubilized by heat-induced coagulation. Chemical investigations on fixation mechanisms of boric acid by egg albumin indicated that both acid-base salt formation occurs, as well as the formation of boric acid-albumin complexes, depending on the boric acid/protein ratio. In treated timber, a chance in protein conformation in presence of boric acid, has been shown by scanning electron microscopy. These mechanisms, partly reversible, while greatly retarding its leaching, leave small amounts of boron free to exercice its activity when needed. Boron leaching as a function of time, appears to tend to an equilibrium value, which one differs in the case of an albumin coagulum alone from what is obtained by leaching treated wood samples. Accelerated biolocical tests using such treated timber have shown that albumin borate used as wood preservative has effectiveness against wood decay, and have durability performances comparable to those obtained with CCA.
M-F Thévenon, A Pizzi, J-P Haluk

Microbial breakdown mechanisms. Mini-Symposium at the 18th IRG meeting, Honey Harbour, Ontario, Canada
1987 - IRG/WP 1327
An understanding of how micro-organisms cause chemical alternation to wood is essential for effective wood preservation. Investigation of the Microbial Breakdown of wood is a very dynamic research field and is increasing in importance as several biocides are being examined as alternativesw to classic wood preservatives. These biocides often do not possess broad spectrum activity. It is esential that the biocides are carefully examined and a good knowledge obtained of how and what they must protect. The aim of this Symposium is to attempt to present an update of research, presented by leaders in the field. The following presentations were held: 1) Intrduction/Overview - L.E. Leightley 2) Morphological observations of brown rot and white rot decay - K. Messner 3) Biochemical aspects or brown and white rot decay - T.L. Highley 4) Influence of variable lignin content on brown rot decay of wood - T. Nilson; G. Daniel 5) Soft rot decay - R.A. Eaton.
L E Leightley

Preliminary studies of the decay mechanism of some brown-rot fungi
1989 - IRG/WP 1402
The importance of the enzymatic degradation of hemicellulose and cellulose by brown-rot fungi is still under discussion. Endo-ß-1,4-xylanase and endoglucanase activities of Coniophora puteana and Poria placenta cultures were measured by the increase in reducing groups. Enzymes were produced in liquid and solid sawdust based culture media. Enzyme activities were measured in two, four and eight week intervals from the beginning of the test. The ability of brown-rot fungi to degrade crystalline and noncrystalline cellulose by an enzymatic pathway was studied by measurement of total cellulase activities from Coniophora puteana and Serpula lacrymans. Low enzyme activities were noted. This result indicates strongly that these fungi possess a complete cellulose-degrading enzymatic pathway.
A-C Ritschkoff, H Viitanen

Biochemical aspects of white-rot and brown-rot decay
1987 - IRG/WP 1319
This paper presents an overview of the decomposition of wood by white- and brown-rot fungi - the most important and potent of known wood-decay fungi. These organisms are unique among cellulose destroyers because of their strong capability to enzymatically degrade lignified material. Special emphasis is given to the following aspects of wood decomposition by white- and brown-rot fungi: (1) effects on the chemical and physical properties of wood, (2) method of invasion and ultrastructural modification of wood, (3) nature and activities of extracellular degrating enzymes, (4) relationship of ultrastructural changes to the degradative enzyme systems, and (5) unique physiological features of the fungi that can be used to control decay.
T L Highley

Fenton's reagent as a modification tool in brown-rot decay
1996 - IRG/WP 96-10155
A biomimetic approach was used to clarify the role and importance of the Fenton-type reaction in the carbohydrate degradation by brown-rot fungi. Spruce sawdust and microcrystalline cellulose were modified in the H2O2/Fe(II) treatment. The degree of hydrolysis of the pretreated spruce sawdust was clearly increased with the complete cellulase (Econase), purified endoglucanase from Trichoderma reesei and endoglucanase of Poria placenta. The oxidative pretreatment of microcrystalline cellulose decreased the hydrolyzability of pure cellulose with the complete cellulase, but the hydrolyzability with both purified endoglucanase of Trichoderma reesei and endoglucanase from Poria placenta was increased. Thus, after oxidative treatment with Fenton's reagent the hydrolysis of both pure cellulose and wood was substantially increased.
M Rättö, A-C Ritschkoff, J Buchert, L Viikari

Production of exraxellular hydrogen peroxide and oxalic acid by brown-rot fungus Poria placenta
1995 - IRG/WP 95-10112
Hydrogen peroxide and oxalic acid have been suggested to be essential in the degradation of wood carbohydrates by brown-rot fungi. Hydrogen peroxide has been suggested to be one of the diffusible low molecular weight agents produced by brown-rot fungi for the degradation of wood carbohydrates by generating highly active radicals. The production of hydrogen peroxide and oxalic acid by Poria placenta was studied on crystalline cellulose, amorphous cellulose and glucose media. Hydrogen peroxide and oxalic acid were clearly produced on culture media containing either amorphous or crystalline cellulose. Hydrogen peroxide and oxalic acid were formed simultaneously and highest amounts of these compounds were obtained on amorphous cellulose. The production of hydrogen peroxide and oxalic acid was surprisingly low on glucose medium.
A-C Ritschkoff, M Rättö, J Buchert, L Viikari

Mechanisms of Protection by NHA Against Fungal Decay
2002 - IRG/WP 02-10429
Treating wood with the water-borne sodium salt of N'-N-naphthaloylhydroxylamine (Na-NHA) protects wood against decay and termite damage. Initial testing indicated little or no inhibition of sapstain fungi, molds, or soft-rot fungi by Na-NHA, suggesting that the mechanism by which this compound protected wood was complex and not that of a broad-spectrum biocide. Previously, we (Green et al, 1997) suggested that the protective mechanism was due to Na-NHA complexing with calcium ions to disrupt fungal metabolism, and/or binding of Na-NHA to the calcium in pit membranes, which acts as a physical barrier to fungal colonization. More recent experiments suggest an alternate mechanism. Specifically, pKa measurements of Na-NHA show that the sodium salt will be essentially fully protonated when impregnated into SYP which is naturally acidic (pH at or below 5.5). Furthermore, the protonated form (H-NHA) was more fungicidal than Na-NHA against two white- and two brown-rot fungi, with the bioactivity approaching that of several commercial organic fungicides. The moderate fungicidal activity of H-NHA is not surprising; the compound is a polyaromatic hydrocarbon much like many of the compounds in creosote. By precipitating mainly at the pit membranes, H-NHA or Ca-NHA serves as a fungicidal barrier to inhibit fungal hyphae from spreading to adjacent cells through the pits. Studies of H-NHA combined with three commercial organic biocides showed that only one combination was synergistic, which further suggests that NHA protects wood by a biocidal mechanism rather than being simply a compound is extremely water insoluble and will thus not leach from wood in outdoor exposure. NHA may also have metal chelating and/or antioxidant properties which further assists in protecting wood. non-biocidal additive.
F Green III, W Henry, T Schultz

Assessing the importance of degradation mechanisms on the loss of effectiveness of wood preservatives
2000 - IRG/WP 00-20193
Accelerated ageing systems developed for application to samples in the laboratory prior to biological tests, should reflect those natural deterioration processes that are likely to occur in the hazard classes defined in EN 335-1. Losses through evaporation or the effects of leaching have been recognised, however their importance, relative to other mechanisms has not been quantified. Degradation mechanisms including photolysis, thermolysis and hydrolysis have largely been ignored. This paper presents information from a study, conducted as part of a project supported by the European Commission (SMT4-CT96-2135), on the relative importance of these different mechanisms through a series of experiments using model compounds. These model compounds were selected because they have known susceptibility to one of the identified degradative mechanisms. TnBTO has been used to monitor photolysis, trihexylene glycol biborate to examine the effects of hydrolysis and lindane to monitor evaporation. The experimental data are compared to semi-natural exposure data. Support for ensuring that the various degradative mechanisms occur in the accelerated ageing systems is recommended.
E D Suttie, R J Orsler, T Dearling

Hydrolysis of bordered pits during colonization of conifers by brown-rot fungi
1995 - IRG/WP 95-10103
Brown-rot decay results in rapid reduction in degree of polymerization (DP) of holocellulose with concomitant strength loss (MOR) without removing lignin. Development of new methods of wood protection will require focusing on early events in the sequence of depolymerization. Bordered pit membranes (sapwood) represent a readily available source of non-lignified carbohydrate, ie. pectin and cellulose. Commercial pectinases (Pectinol) and Trichoderma sp. have been shown to degrade pit membranes and increase penetration of preservatives. Brown-rot fungi have previouely been shown to produce oxalic acid (OA) during the decay process. Plant pathogens have been shown to degrade pectin by the synergistic action of OA and polygalacturonase (PG). The OA solubilizes the pectin by chelating the Ca++ and the PG hydrolyses the a-1,4 linkages. We have demonstrated the ability of Postia placenta, Gloeophyllum trabeum and Serpula incrassata to use pectin as a sole carbon sourse and to produce OA and PG on both liquid media and wood. Aspergillus niger and Trichoderma sp. also produce PG on wood but no OA or weight loss. The optimal pH of brown-rot polygalacturonase activity is circa 4.0. As the pH of the wood drope below pH 4, due to acid production during decay, there is a progressive decrease in PG activity and the possibility of acid catalyzed hydrolysis of pit membranes is suggested by increased permeability. We hypothesize that pectin utilization is an essential step during incipient brown-rot decay which helps to initiate fungal metabolism and promote the spread of fungal hyphae between tracheids.
F Green III, J L Tschernitz, T A Kuster, T L Highley

Copper based wood preservative - A new approach using fixation with resin acids of rosin
2000 - IRG/WP 00-30249
Copper soaps with carboxylic acid groups of resin acids of rosin were shown to be potential long-term wood preservatives. The principle involved is the attachment of copper to the network formed by the inorganic part of the preservative (rosin) through the -COOH groups. The mechanisms of fixation have been studied, and it has been shown that this association could be obtained : (1) by forming the salt (a mix of rosin and NaOH where CuSO4 is added), and then impregnate (with a vacuum/pressure system) the wood with this product dissolved in ethanol, or (2) by using a double impregnation system with water solutions of the mix rosin-NaOH first, and a CuSO4 solution second, the salt being then formed within the timber. The biocidal mechanisms are based on the realease of Cu2+ by hydrolysis of the -(COO - )2Cu2+ when very humid conditions occur, this being reversible when wood moisture content is decreasing. Treated wood mini-blocks have shown good performances when leached, and biological tests assessed the good durability of such treated and leached timber.
C Roussel, J P Haluk, A Pizzi, M-F Thévenon

Examination of preservative-treated Pinus sylvestris using electron paramagnetic resonance
1992 - IRG/WP 92-3710
EPR is currently being used to help elucidate the nature and extent of the chemical reactions occurring between wood and copper based timber preservatives. In the work reported here treated Scots pine samples were examined at room temperature and in the frozen state. Plots of the electronic parameters A|| vs. g|| were found to be a useful index of the electronic properties of the various formulations. Those containing copper bound to nitrogen could clearly be distinguished from chromated-copper and other nitrogen-free systems and the technique was extremely useful in the interpretation of spectra where a formulation generated more than one copper signal. In two of the nitrogen containing systems one of the forms of copper, identified as being bound to nitrogen was well fixed whereas the other form, not bound to nitrogen, was more leachable. In the chromated-copper formulations tested (CC and CCA) a small amount of the chromium was identified as a stable concentration dependent Cr(V) species (g = 1.974 - 1.978) which presumably disproportionates during leaching into Cr(III) and Cr(VI). In general, chromated copper formulations gave poor quality spectra in comparison to copper only formulations and this should allow the newer, chromium free preservatives to be more widely studied by EPR.
A S Hughes, R J Murphy, J F Gibson, A J Cornfield

The identification of the carbohydrate degrading enzymes from the crude extract of brown-rot fungus Gloeophyllum trabeum
1991 - IRG/WP 1483
The brown-rot fungus, Gloeophyllum trabeum, produces a pattern of carbohydrate degrading enzymes during the wood decay. In liquid sawdust media the activities of endo-b-1,4-gluganase and endo-b-1,4-xylanase were at the maximum after 5-6 weeks cultivation. The production of enzymes started immediately after inoculation suggesting that the degradation of hemicellulose and easily degradable parts of cellulose is an initial step of wood decomposition.
A-C Ritschkoff, J Buchert, L Viikari

Chemical reactions involved in furfurylation of solid wood - An investigation by ATR-IR spectroscopy
2006 - IRG/WP 06-40347
Wood modification with furfuryl alcohol (FA) has gained renewed interest during the last five to ten years because of advances in process technology and because of increased focus on the environmental hazards of traditional wood impregnation. The reaction mechanisms involved in the furfurylation process are not yet understood in detail. In the work presented here, the chemical reactions and their end products in the wood cell wall were studied using Attenuated Total Reflection InfraRed spectroscopy (ATR-IR) and knowledge from molecular modelling. Evidence of a polymeric structure of FA in the cell wall was found, but bonding between wood constituents and FA or a FA-polymer could not be verified. Because of many overlapping absorbance peaks in the IR region, wood and FA absorbance bands are difficult to assign without support from extensive molecular modelling. Further modelling is needed to fully understand the possible reactions between wood and FA.
T Mark Venås, L Garbrecht Thygesen, S Barsberg

Protection mechanisms of modified wood against decay by white and brown rot fungi
2010 - IRG/WP 10-10713
The resistance of beech and pine wood blocks treated with 1,3-dimethylol-4,5-dihydroxyethylene urea (DMDHEU) against T. versicolor and C. puteana increased with increasing WPG. Full protection (mass loss below 3%) was reached at WPGs of approximately 15% (beech) and 10% (pine). Metabolic activity of the fungi in the wood blocks was assessed as heat or energy production determined by isothermal micro-calorimetry. Fungal activity in the wood decreased with increasing WPG. Still, activity was detected even in wood blocks of highest WPG and showed that the treatment was not toxic to the fungi. The infiltration of untreated and DMDHEU-treated wood blocks with nutrients and thiamine prior to fungal incubation did not result in an increased mass loss caused by the fungi. This shows that the destruction or removal of nutrients and vitamins during the modification process has no influence on fungal decay. In order to study the effect of cell wall bulking and increased surface area, the cell wall integrity was partly destroyed by milling and the decay of the fine wood flour was compared to that of wood mini-blocks. The mass losses caused by the fungi, however, also decreased with increasing WPG and showed comparable patterns like in the case of mini-blocks.To study the effect of the chemical change of cell wall polymers, cellulose was treated with DMDHEU and the product was subjected to hydrolysis by a cellulase preparation. The release of sugar during the incubation was clearly reduced as compared to untreated cellulose. Pre-treatment of modified cellulose with Fenton’s reagent increased the amount of released sugar due to the cellulase activity. Pine micro-veneers were subjected to Fenton’s reagents in acetate buffer over 48h. While untreated specimens and veneers treated with low DMDHEU concentration displayed strong and steady tensile strength loss, veneers treated to a higher WPG did hardly show tensile strength loss.
C Mai, P Verma, Yanjun Xie, J Dyckmans, H Militz

Fungal Attack on Lignin and Cellulose: Elucidation of Brown- and White-Rot Mechanisms Comparing Biomimetic and In-Vivo Degradation Patterns
2010 - IRG/WP 10-10714
This paper examines research and hypotheses that have been developed over several years on wood degradation mechanisms. This information is combined with new data and analyses to explain why wood decay patterns caused by brown-rot fungi and specific types of white-rot fungi are different. New data, including work with both biomimetic studies on low molecular weight compounds, degradative enzymes, and wood decayed by brown- and white-rot fungi support a role for these compounds, which results in different types of fungal decay. Specifically the presence or absence of low molecular weight phenolate compounds that bind and reduce iron to generate oxygen radicals is related to brown-rot, as well as “selective white-rot” decay of wood. Free radicals generated by the low molecular weight systems are important in opening up the structure of wood in advance of, or concurrent with, enzymatic attack in both brown-rot and selective white-rot decay. “Simulataneous white-rot” fungi do not typically posses a highly expressed low molecular weight phenolate system and this may help to explain the erosion pattern of decay observed in decay by this type of white-rot. New analytical techniques including Pyrolysis-molecular beam mass spectrometry and 13C-labeled tetramethylammonium hydroxide thermochemolysis are used to provide new information, particularly regarding how lignin is attacked, and either repolymerized or solubilized depending on the type of fungal attack. Discussion of the mechanisms involved, and how new wood protection schemes may be developed to exploit these mechanisms is reviewed.
V Arantes, B Goodell, A M F Milagres, Yuhui Qian, T Filley, J Jellison, S Kelley

A survey of factors affecting decay resistance of wood modified with acetic anhydride
2012 - IRG/WP 12-40594
From the range of information published, acetylation appears well suited to provide adequate protection against biological attack for materials derived from typically non-durable wood species. Acetylated wood is now commercially available both in Europe and in the USA. But still there are a lot of unanswered questions related to fungal decay mechanisms in acetylated wood. The paper summarize existing knowledge and highlight future research opportunities related to fungal deterioration of acetic anhydride modified wood. In addition statistical analyses based on previously published data were performed to quantify what factors contribute most to the performance (calculated as test sample/control). The results showed that WPG can explain approximately 50 % of the performance, measured as test sample/control (T/C), for acetic anhydride treated wood. Other of the applied variables, like wood species or type of fungus can reduce the variance in T/C by additional 15 %.
G Alfredsen, P O Flæte, H Militz

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

Enhancing Our Understanding of Brown Rot Mechanisms through Catalytic Pretreatment and Cellulase Cocktail
2018 - IRG/WP 18-10909
A catalytic mechanism, described as the “chelator-mediated Fenton” (CMF) mechanism, is proposed to mimic the non-enzymatic action of brown rot fungi. A CMF treatment was used together with an enzymatic cocktail to study how wood was deconstructed and solubilized. This was done in-part to determine if the treatment mimicked the action of brown rot fungi, but also to explore improved treatment processes for bioprocessing of woody biomass. Our data suggest that the CMF mechanism is highly efficient in overcoming the lignin recalcitrance barrier to solubilize wood. Multiple pulses (up to 4 pulses) of CMF treatment were able to solubilize a majority of both the lignin and cellulose of wood at room temperature, using a hydrogen peroxide concentration of only 1%. Using a single pulse of the CMF system as a pretreatment allowed more wood residue to be retained, and enzymatic action on this pretreated wood was enhanced compared to control wood. In separate experiments, significantly greater solubilization of both sugars and lignin occurred when a single-pulse CMF pretreatment was used prior to enzymatic action than by enzymatic action alone on unmodified wood. This work suggests a key reason why the brown rot fungi have abandoned many of their extracellular enzymes to produce only a select suite of cellulases, which the fungus employs after prior modification of the cell wall using a CMF mechanism. This research further suggests that the CMF mechanism may have potential to be adapted for bioprocessing of woody biomass to produce sustainable fuels and bioproducts in the future.
S Tabor, L Orjuela, D Contreras, G Alfredsen, J Jellison, S Renneckar, B Goodell

Non-stochiometric oxidation and ROS generation promoted by guaiacol lignin structures and lignocelluose surfaces may be a component of brown rot fungal degradation mechanisms
2019 - IRG/WP 19-10937
Model guaiacol compounds representing lignin monomers, as well as DHP-lignin and wood flour of controlled particle size were used to assess iron reduction at the pH of the natural wood cell wall. All compounds functioned as electron donors for ferric iron, with the lignin monomers demonstrating capacity for non-stochiometric reduction of iron with multiple moles of ferric ion reduced per mole of lignin monomer. Iron reduction was enhanced as pH decreased. The results provide a mechanism to explain how lignin may participate as part of a “moving radical front” after initial fragmentation of the lignocellulose cell wall by brown rot fungi. Further, relative to enzymatic action on wood, the data suggest a mechanism to generate electrons that would promote action by fungal enzymes that require an electron donor. The data also demonstrate how hydroxyl radicals would be generated to promote the generation of low levels of formaldehyde from lignin under conditions when lignin surfaces were exposed.
Y Tamarua, M Yoshidaa, L D Eltisb, B Goodell

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