Wheat straw (Triticum sativum) and poplar wood (Liriodendron tulipifera) were subjected to biomimetic oxidative pretreatment in aqueous organic solvent at mild condition. To enhance the biomass conversion efficiency, influences of different coordinated copper (II) complexes and organic solvents on hydrolysable sugar yield, residual lignin content and biogas potential were investigated. The screening study of copper complexes showed that the pretreatment system in the presence of Cu/dpa complexes gave the best results among all other coordinators on accelerating the oxidative lignin degradation when hydrogen peroxide was used as an oxidant yielding 409.7 mg g -1 or 63.7% theoretical reducing sugar yield based on total polysaccharides of untreated wheat straw after 48-h enzymatic hydrolysis. Delignification of wheat straw in isopropanol/water mixture catalyzed Cu/dpa/H2O2 system improved both lignin removal and lignin depolymerization efficiencies which subsequently led to higher yield of hydrolysable reducing sugars. Reducing sugar yield of 548.7 mg g -1 (85.3% theoretical yield) and 11.3% total residual lignin content (43.8% lignin removal) were obtained from the Cu/dpa/H2O2 pretreatment system in isopropanol/water mixture. However, less effect was observed for poplar wood biomass pretreatment in all particle sizes tested. Keyword: Biomass pretreatment, lignocelluloses delignification, wheat straw, poplar wood, coordinated-copper complex, aqueous organic solvent system, oxidative lignin degradation, organosolv system

Wheat straw (Triticum aestivum L.) and oat straw (Avena sativa L.) were subjected to acid and alkaline pre-treatments partly in combination with hydrogen peroxide. The aim was to remove lignin and increase the accessibility of the polysaccharides to enzymatic digestion. Accessibility was evaluated by digestion with a cell wall degrading enzyme complex to yield reducing sugars that may serve as precursor substrates for biofuels or building block chemicals. Changes in lignin, hemicelluloses, as well as amorphous, semi-crystalline, and crystalline regions of cellulose moieties of pretreated straw were efficiently characterized by Fourier transform near-infrared (FT-NIR) reflectance spectroscopy. These alterations of the chemical structure of straw after different pre-treatment methods were powerfully differentiated by principal component analysis (PCA). Characteristics of the different samples owing to the different pretreatment methods could be clustered from the PCA loadings spectra.

Melanin is chemically and by physical characteristics very similar to lignin, a major constituent of wood, and therefore ligninolytic enzymes of white-rot fungi were tested for their ability to selectively degrade melanin. Melanin degradation was studied both in liquid suspensions of melanin and on melaninised paper samples. Liquid suspension samples were tested for changes in their chemical composition (appearance and relative representation of functional groups and chemical bonds) with FTIR spectrometry. Changes in colour of melaninised paper samples were investigated with a colorimeter. Effectiveness of the treatment (bleaching) was determined as a change in lightness (ΔL). Melanin was oxidised in the liquid suspensions, and the intensity of modification varied depending on the procedure employed. The most pronounced changes in melanin were observed in laccase-1-hydroxybenzotriazole (HBT) treatment at heightened air pressure. The most prominent discoloration of the melaninised paper samples (and no visually detectable damage to the integrity of the paper) was, like in the case of the liquid suspensions, observed after laccase-HBT treatment.

Laccase enzyme was produced from an isolate of the white rot fungus, Ganoderma lucidum Chaaim-001 BCU. The enzyme was subsequently evaluated for its degradative ability towards sixteen types of polycyclic aromatic hydrocarbons (PAHs). The G. lucidum laccase degraded antracene completely with or without a redox mediator (2 mM 1-hydroxybenzotriazole) and also degraded benzo[a] pyrene, fluorine, acenapthene, acenaphthylene and benzo[a] anthracene up to 100.0, 98.6, 95.4, 90.1 and 85.3 %, respectively, when the mediator was present. In the absence of the mediator, the ability to degrade these compounds dropped to 71.71, 62.9, 80.49, 85.85 and 9.14% respectively. Compared to the laccase enzyme from Trametes vesicolor, G. lucidum laccase appeared to retain more of its capability to degrade these PAHs when the mediator was absent.

Abstract Sapstain fungi, which reduce the value of pine wood, were isolated from an industrial wood yard in north-eastern Germany. The predominant wood discolouring species on the industrial wood yard and in the forests of the investigated region was Sphaeropsis sapinea (syn. Diplodia pinea), but Ophiostoma minus was also found. These fungi were challenged with antagonistic micro-organisms in laboratory trials and in field experiments. Amongst the tested microorganisms only strains of filamentous fungi (Trichoderma sp. and Phlebiopsis gigantea) could control the sapstain fungi on pine wood blocks efficiently. Although P. gigantea was unable to inhibit stain formation completely, the wood was bleached by this fungus in later incubation stages. In two field trials, sapstain on pine wood logs was successfully retarded for a period of 10 and 12 weeks, respectively, with a white sporulating mutant of Trichoderma harzianum. Thus, the concept using filamentous fungi as antagonists against sapstain developed under laboratory conditions also proved to be valid under natural conditions in forest eco-systems.

Several analytical methods were compared to evaluate characteristic wood decaying fungi for their potential to depolymerise lignin on spruce wood particles. Wood samples were treated with the white rot fungi Phlebia brevispora, Ceriporiopsis subvermispora, Merulius tremellosus, Pycnoporus sanguineus, Trametes pubescens and with the brown rot fungus Gloeophyllum trabeum. The UV absorbancies of crude ethanol extracts, total extractives content from sequential extraction, ligninolytic enzyme activities, lignin solubilisation and decrease of lignin content were compared. It was shown, that, in early decay stages, UV absorbancies of crude ethanol extracts and total extractives content correlate well with lignin degradation, increase of acid soluble lignin and increased production of ligninolytic enzymes (total peroxidase). Lignin content was determined using FT-NIR spectroscopy as well as by wet-chemical analysis, indicating a very good correlation between the two methods. According to the different analytical methods, the tested fungi can be classified into three categories based on their characteristic behaviour: brown rot, “slow” and “fast” white rot.

A selective white rot fungus, Ceriporiopsis subvermispora is shown to, degrade lignin without extensive damage to cellulose. This selective ligninolysis reaction is catalyzed by low molecular mass compounds at a site far from the enzymes. At an incipient stage of the wood decay, the fungus catalyzed in situ lipid peroxidation and secreted alkylitaconic acids and ceriporic acids. The extracellular metabolites are thought to attenuate the iron redox reactions, thereby inhibiting the production of a cellulolytic active oxygen species such as hydroxyl radicals. The selective lignolysis by this fungus can be applied to pretreatments of wood for ethanol fermentation, methane fermentation and feedstuff production.

Wood is colonised and degraded by a variety of microorganisms, the most efficient ones are wood-rotting basidiomycetes. Microbial decay processes cause damage to wooden constructions, but also have great potential as biotechnological tools to change the properties of wood surfaces and of sound wood. Standard methods to evaluate changes in infected wood, e.g., EN350-1 1994, are time-consuming. Rapid FT-NIR spectroscopic methods are also suitable for this purpose. In this paper, degradation experiments on surfaces of spruce (Picea abies L. Karst) and beech (Fagus silvatica L.) were carried out with white rot basidiomycetes or the ascomycete Hypoxylon fragiforme. Experiments with brown rot or soft rot caused by Chaetomium globosum were also performed. FT-NIR spectra collected from the degraded wood were subjected to principal component analysis. The lignin content and mass loss of the specimens were estimated based on univariate or multivariate data analysis (partial least squares regression).

Summary Microbial mechanisms of lignin degradation may be utilised for solid-state fermentations other than biopulping, during which the selective conversion of lignin is required. The current paper reviews current work into selective lignin conversion, with emphasis on the contributions made by our research group, which consists of researchers from five different laboratories. Three of them cooperate within Wood K plus. The recent research of this group has focussed on fermentations utilising the unique metabolism of selective white-rot fungi to modify wood surfaces during relatively short fermentation times of less than one week and on research into the molecular mechanisms causing these modifications. Lignin degradation by selective fungi (e.g. Ceriporiopsis subvermispora and species of the genus Phlebia) on the wood surfaces was significant after three days. After seven days the overall lignin content of spruce wood shavings was reduced by more than 3.5 %. Lignin loss was accompanied by an increase of extractable substances. To evaluate small changes and to trace the fungal modification processes, Fourier transform infrared spectroscopic (FTIR) techniques and electron paramagnetic resonance (EPR) spectroscopy were applied and adapted. The spectra recorded in the near infrared region (FT-NIR) turned out to be very useful for kinetic studies of the biopulping/biomodification processes and a good method to evaluate the capabilities of fungi to modify wood surfaces within this short period.