No abstract

No abstract

No abstract

Eucalyptus globulus wood was subjected to autohydrolysis pretreatment at different severity factors. The pretreated materials were enzymatically saccharified at a substrate load of 10% (w/v) using a cellulase enzyme complex. Around 82-95% of original glucans were retained in the pretreated material, and the enzymatic hydrolysis yields ranged from 58% to 90%. The chemical and structural changes in the pretreated materials were investigated by microscopic (SEM, LSCM) and spectroscopic (2D-HSQC NMR and FT-IR) techniques. 2D-NMR results showed a reduction in the amounts of β-O-4 aryl-ether linkages and suggested the presence of newly condensed structures of lignin in the biomass pretreated at the more severe conditions. Furthermore, the microscopic analysis showed that lignin migrates out of the cell wall and re-deposits in certain regions of the fibers at the more severe conditions to form droplet-like structures and expose the cellulose surface. These changes improved the glucose yield up to 69%, on dry wood basis.

No abstract

Although lignin is recalcitrant, some specialized fungi developed the ability to degrade this complex molecule. Most of these fungi belong to the basidiomycetes and are responsible for the white-rot decay process (19). White-rot fungi use an intricate oxidative complex to degrade lignin, which is based on oxidative enzymes and low-molecular-mass mediators (28). Several white-rot fungi produce a lignin peroxidase (LiP) that can initiate one-electron oxidation of nonphenolic arylglycerol-␤-O-aryl ether units. This oxidation is followed by C␣-C␤ or ␤-O-aryl cleavage to give aromatic aldehydes or phenylglycerols, respectively, as primary products (19). On the other hand, some white-rot fungi degrade lignin efficiently without producing LiP (20). One of them, Ceriporiopsis subvermispora, has been extensively studied (15,16,17,31,32), owing to its suitability for biopulping (1,27). Although the industrial applicability of this fungus has been recognized, its ligninolytic strategies are not completely understood. It has often been assumed that lignin degradation by C. subvermispora is dependent on manganese-dependent peroxidases and laccases (28). The occurrence of lignin degradation inside the wood matrix during the first stages of wood decay, when low cell wall permeability does not permit enzyme diffusion, has clearly indicated that some low-molecular-mass agents also act in the early stages of lignin biodegradation (2). Lipid peroxidation induced by manganese-dependent peroxidase has been proposed for lignin biodegradation by C. subvermispora (6,17,18,32). Studies with lignin model compounds have shown that nonphenolic arylglycerol-␤-O-aryl units are disrupted by means of one-electron oxidation mechanisms similar to the routes proposed for basidiomycetes that produce LiP (18,32).Under solid-state fermentation of wood, C. subvermispora extensively depolymerizes lignin. Lignin depolymerization has been demonstrated in studies based on the molecular mass distribution of milled wood lignins (MWLs) recovered from biotreated wood samples (15) and in studies using in situ derivatization followed by reductive cleavage (DFRC) of lignin in biotreated wood, which indicates lignin depolymerization as a consequence of aryl-ether degradation (16).The present study provides additional data for evaluating lignin biodegradation by C. subvermispora during solid-state fermentation of Pinus taeda wood. The structural characteristics of MWLs extracted from sound (untreated) and biotreated wood samples were elucidated using wet-chemical and spectroscopic analyses. MATERIALS AND METHODSFungus, inoculum preparation, and wood biodegradation. C. subvermispora (Pilat) Gilbertson et Ryvarden cultures were maintained on 2% (wt/vol) malt extract agar plates at 4°C. The wood chips (approximately 2.5 by 1.2 by 0.2 cm) used in this work came from a single log of a 28-year-old P. taeda tree.Biodegradation experiments were carried out in 20-liter polypropylene bioreactors. Precolonized wood chips were used as inoculum seed to start the colonization ...

Microorganisms capable of accumulating lipids in high percentages, known as oleaginous microorganisms, have been widely studied as an alternative for producing oleochemicals and biofuels. Microbial lipid, so-called Single Cell Oil (SCO), production depends on several growth parameters, including the nature of the carbon substrate, which must be efficiently taken up and converted into storage lipid. Οn the other hand, substrates considered for large scale applications must be abundant and of low acquisition cost. Among others, lignocellulosic biomass is a promising renewable substrate containing high percentages of assimilable sugars (hexoses and pentoses). However, it is also highly recalcitrant, and therefore it requires specific pretreatments in order to release its assimilable components. The main drawback of lignocellulose pretreatment is the generation of several by-products that can inhibit the microbial metabolism. In this review, we discuss the main aspects related to the cultivation of oleaginous microorganisms using lignocellulosic biomass as substrate, hoping to contribute to the development of a sustainable process for SCO production in the near future.

Ganoderma australe is a white-rot fungus that causes a selective wood biodelignification in some hardwoods found in the Chilean rainforest. Ceriporiopsis subvermispora is also a lignin-degrading fungus used in several biopulping studies. The enzymatic system responsible for lignin degradation in wood can also be used to degrade recalcitrant organic pollutants in liquid effluents. In this work, two strains of G. australe and one strain of C. subvermipora were comparatively evaluated in the biodegradation of ABTS and the dye Poly R-478 in liquid medium, and in the pretreatment of Eucalyptus globulus wood chips for further kraft biopulping. Laccase was detected in liquid and wood cultures with G. australe. Ceriporiopsis subvermispora produce laccase and manganese peroxidase when grown in liquid medium and only manganese peroxidase was detected during wood decay. ABTS was totally depleted by all strains after 8 days of incubation while Poly R-478 was degraded up to 40% with G. australe strains and up to 62% by C. subvermispora after 22 days of incubation. Eucalyptus globulus wood chips decayed for 15 days presented 1-6% of lignin loss and less than 2% of glucan loss. Kraft pulps with kappa number 15 were produced from biotreated wood chips with 2% less active alkali, with up to 3% increase in pulp yield and up to 20% less hexenuronic acids than pulps from undecayed control. Results showed that G. australe strains evaluated were not as efficient as C. subvermispora for dye and wood biodegradation, but could be used as a feasible alternative in biotechnological processes such as bioremediation and biopulping.