Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “LIGNIN”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 1,477 records · Page 82Linked to original sources
PubMed1995

Manganese peroxidase from Phanerochaete chrysosporium. A homology-based molecular model.

A detailed three-dimensional model of manganese peroxidase was constructed using lignine peroxidase as the structural scaffold. This is the only protein in the peroxidase family except for cytochrome c peroxidase for which a resolved crystal structure is available. The model was built using the following procedure: (a) structurally preserved regions were derived from similar regions in the sequence alignment of the two proteins; (b) non-similar regions were modelled by searching a set of resolved protein structures for fragments which fitted in geometrically and choosing the best fitting fragment. Side chains were constructed by calculating rotamer-rotamer interaction energies and minimizing intramolecular energy. Model refinement was performed by molecular mechanics calculation. The quality of the model was assessed on the basis of the propensity of the amino acids to be inserted into regular secondary-structure elements and to be exposed to solvent. All the lignine peroxidase regions not used for model construction because of the lack of similarity, except the helix fragment Leu261-Phe269, correspond to external loops, suggesting reliable modelling. The manganese peroxidase model structure was analyzed in detail and several functionally relevant structural features were predicted, the most important being: (a) the very close structural similarity between lignine and manganese peroxidase active sites, suggesting a similar mode of hydrogen peroxide activation; (b) the substitution of polar residues for the hydrophobic amino acids exposed at the edge of the channel involved in substrate recognition in lignine peroxidase, suggesting that manganese peroxidase does not directly bind aromatic substrates; (c) the location of residues potentially able to bind Mn2+, spatially positioned on the side of the 3-CH3 heme edge.

Amino Acid Sequence↗
PubMed1980

Mineralization of detrital lignocelluloses by salt marsh sediment microflora.

Specifically radiolabeled C-(cellulose)-lignocellulose and C-(lignin)-lignocellulose were isolated from labeled cuttings of Spartina alterniflora (cordgrass) and Pinus elliottii (slash pine). These were used to estimate the rates of mineralization to CO(2) of lignocelluloses of estuarine and terrestrial origin in salt marsh estuarine sediments. The lignin moiety of pine lignocellulose was mineralized 10 to 14 times more slowly than that of Spartina lignocellulose, depending on the source of inoculum. Average values for percent mineralization after 835 h of incubation were 1.4 and 13.9%, respectively. For Spartina lignocellulose, mineralization of the cellulose moiety was three times faster than that of the lignin moiety. Average values for percent mineralization after 720 h of incubation were 32.1 and 10.6%, respectively. Lignocellulose and lignin contents of live pine and Spartina plants were analyzed and found to be 60.7 and 20.9%, respectively, for pine and 75.6 and 15.1%, respectively, for Spartina.

Journal Article↗
PubMed1981

Degradation of softwood, hardwood, and grass lignocelluloses by two streptomyces strains.

Two Streptomyces strains, S. viridosporus T7A and S. setonii 75Vi2, were grown on softwood, hardwood, and grass lignocelluloses, and lignocellulose decomposition was followed by monitoring substrate weight loss, lignin loss, and carbohydrate loss over time. Results showed that both Streptomyces strains substantially degraded both the lignin and the carbohydrate components of each lignocellulose; however, these actinomycetes were more efficient decomposers of grass lignocelluloses than of hardwood or softwood lignocelluloses. In particular, these Streptomyces strains were more efficient decomposers of grass lignins than of hardwood or softwood lignins.

Journal Article↗
PubMed1982

Effects of petroleum hydrocarbons on plant litter microbiota in an arctic lake.

The effects of petroleum hydrocarbons on the microbial community associated with decomposing Carex leaf litter colonized in Toolik Lake, Alaska, were examined. Microbial metabolic activity, measured as the rate of acetate incorporation into lipid, did not vary significantly from controls over a 12-h period after exposure of colonized Carex litter to 3.0 ml of Prudhoe Bay crude oil, diesel fuel, or toluene per liter. ATP levels of the microbiota became elevated within 2 h after the exposure of the litter to diesel fuel or toluene, but returned to control levels within 4 to 8 h. ATP levels of samples exposed to Prudhoe Bay crude oil did not vary from control levels. Mineralization of specifically labeled C-[lignin]-lignocellulose and C-[cellulose]-lignocellulose by Toolik Lake sediments, after the addition of 2% (vol/vol) Prudhoe Bay crude oil, motor oil, diesel fuel, gasoline, n-hexane, or toluene, was examined after 21 days of incubation at 10 degrees C. Diesel fuel, motor oil, gasoline, and toluene inhibited C-[lignin]-lignocellulose mineralization by 58, 67, 67, and 86%, respectively. Hexane-treated samples displayed an increase in the rate of C-[lignin]-lignocellulose mineralization of 33%. C-[cellulose]-lignocellulose mineralization was inhibited by the addition of motor oil or toluene by 27 and 64%, respectively, whereas diesel fuel-treated samples showed a 17% increase in mineralization rate. Mineralization of the labeled lignin component of lignocellulose appeared to be more sensitive to hydrocarbon perturbations than was the labeled cellulose component.

Journal Article↗
PubMed1985

Factors Involved in the Regulation of a Ligninase Activity in Phanerochaete chrysosporium.

The regulation of an H(2)O(2)-dependent ligninolytic activity was examined in the wood decay fungus Phanerochaete chrysosporium. The ligninase appears in cultures upon limitation for nitrogen or carbohydrate and is suppressed by excess nutrients, by cycloheximide, or by culture agitation. Activity is increased by idiophasic exposure of cultures to 100% O(2). Elevated levels of ligninase and, in some cases, of extracellular H(2)O(2) production are detected after brief incubation of cultures with lignins or lignin substructure models, with the secondary metabolite veratryl alcohol, or with other related compounds. It is concluded that lignin degradation (lignin --> CO(2)) by this organism is regulated in part at the level of the ligninase, which is apparently inducible by its substrates or their degradation products.

Journal Article↗
PubMed1986

Palo Podrido: Model for Extensive Delignification of Wood by Ganoderma applanatum.

Chemical and micromorphological analysis revealed that South Chilean "palo podrido" results from a white-rot fungus that causes highly selective and extensive delignification. Palo podrido samples from 10 different hardwood trunks (Eucryphia cordifolia, Drimys winteri, and Nothofagus dombeyi) decayed by Ganoderma applanatum were analyzed. Of 14 samples, 11 had extremely low Klason lignin values, ranging from 6.1 to 0.4% (dry weight). The most remarkable and unusual feature was that delignification and defibration were not restricted to small pockets but extended throughout large areas in the interior of trunks subjected to undisturbed rotting over long periods of time. Comparative analysis of water content, swelling capacity, and lignin content led to the conclusion that besides lignin degradation, suppression of the cellulolytic activity of the rotting organisms plays a decisive role. Among various nutrients added to a palo podrido sample (3% residual Klason lignin), the nitrogen source was the only one leading to almost complete cellulose degradation. We suggest that the extremely low nitrogen content (0.037 to 0.073% [dry weight]) of the investigated wood species was the primary cause for the extensive delignification as well as the concomitant suppression of cellulose breakdown. The low temperatures, high humidity, and microaerobic conditions maintained within the decaying trunks are discussed as additional ecological factors favoring delignification in South Chilean rain forests.

Journal Article↗
PubMed1989

Relationship between Fungal Biomass Production and the Brightening of Hardwood Kraft Pulp by Coriolus versicolor.

The white-rot fungus Coriolus versicolor increased the brightness of hardwood kraft pulp by two mechanisms depending on the concentration of available nitrogen. In low-nitrogen conditions, the brightening process was a chemical effect mediated by the fungus, associated with the removal of residual lignin in the pulp; kappa number was used as an indicator of lignin concentration. A five-day treatment in low-nitrogen conditions increased the brightness of hardwood kraft pulp from 36.2 to 54.5%, with a corresponding decrease in kappa number from 12.0 to 8.5, equivalent to a reduction in the lignin concentration from ca. 2.0% (wt/wt) to ca. 1.4% (wt/wt). Under these conditions, we concluded that the brightening of the pulp was a secondary metabolic event initiated after the depletion of available nitrogen. This method of brightening has been described as bleaching or biobleaching. By contrast, in high-nitrogen conditions, the brightening was a physical effect associated with the dilution of the dark pulp fibers by the relatively high levels of brighter fungal mycelium produced. Since this method of brightening was not evidently associated with lignin removal, it cannot be described as bleaching. In pulp samples brightened in high-nitrogen conditions, as brightness increased, there was a corresponding increase in kappa number. This observation was explained by the consumption of potassium permanganate by the fungal mycelium, which interfered with kappa number determinations at high fungal biomass levels.

Journal Article↗
PubMed1990

Comparative studies of delignification caused by ganoderma species.

Isolates of six species of Ganoderma in the G. lucidum complex were evaluated for their ability to decay wood of Quercus hypoleucoides A. Camus and Abies concolor (Gord. and Glend.) Lindl. ex. Hildebr. by using in vitro agar block decay tests. Morphological, ultrastructural, and chemical studies of decayed wood were used to determine the extent of delignification or simultaneous decay caused by each species of Ganoderma. All species decayed both white fir and oak wood; however, less percent weight loss (%WL) occurred in white fir than oak. In white fir, isolates of two undescribed Ganoderma species (RLG16161, RLG16162, JEA615, and JEA625) caused significantly higher%WL (21 to 26%) than that in G. colossum, G. oregonense, G. meredithiae, and G. zonatum (10 to 16%). Only Ganoderma sp. isolates JEA615 and JEA625 caused delignification, with JEA615 causing a lignin-to-glucose gram loss ratio of 1.6:1. Morphological and ultrastructural studies confirmed delignification by this fungus and showed that some delignification had occurred by all of the species, although areas of delignification were limited to small regions adjacent to simultaneously decayed cells. In oak, G. colossum caused significantly less%WL (22 to 35%) than the other species (38 to 52%). All of the species, except G. meredithiae, caused delignification with lignin-to-glucose gram loss ratios ranging from 1.4 to 4.9:1. Extensive delignification by isolates of G. colossum and G. oregonense was observed; moderate delignification was caused by the other species. Ganoderma meredithiae caused a simultaneous decay, with only small localized regions of cells delignified, while delignification by G. zonatum was irregular, with specific zones within the cell wall delignified. The thermophilic and chlamydosporic G. colossum has the capacity to cause extensive delignification and appears ideally suited for use in lignin degradation studies and biotechnological applications of lignin-degrading fungi.

Journal Article↗
PubMed1993

Microbial delignification with white rot fungi improves forage digestibility.

Three wild-type white rot fungi and two cellulase-less mutants developed from Phanerochaete chrysosporium K-3 (formerly Sporotrichum pulverulentum) were tested for their ability to delignify grass cell walls and improve biodegradation by rumen microorganisms. Fungal-treated and control stems of Bermuda grass were analyzed for their content of ester- and ether-linked aromatics by using alkali extraction and gas chromatography, for in vitro dry weight digestion and production of volatile fatty acids in in vitro fermentations with mixed ruminal microorganisms, for loss of lignin and other aromatics from specific cell wall types by using microspectrophotometry, and for structural changes before and after in vitro degradation by rumen microorganisms by using transmission electron microscopy. P. chrysosporium K-3 and Ceriporiopsis subvermispora FP 90031-sp produced the greatest losses in lignin and improved the biodegradation of Bermuda grass over that of untreated control substrate. However, C. subvermispora removed the most lignin and significantly improved biodegradation over all other treatments. Phellinus pini RAB-83-19 and cellulase-less mutants 3113 and 85118 developed from P. chrysosporium K-3 did not improve the biodegradation of Bermuda grass lignocellulose. Results indicated that C. subvermispora extensively removed ester-linked p-coumaric and ferulic acids and also removed the greatest amount of non-ester-linked aromatics from plant cell walls. Microscopic observations further indicated that C. subvermispora removed esters from parenchyma cell walls as well as esters and lignin from the more recalcitrant cell walls (i.e., sclerenchyma and vascular tissues). C. subvermispora improved in vitro digestion and volatile fatty acid production by ruminal microorganisms by about 80%, while dry matter loss due to fungi was about 20% greater than loss in untreated control stems. The chemical and structural studies used identified sites of specific fungal attack and suggested mechanisms whereby improvement occurred.

Journal Article↗
PubMed1993

Is an activator protein-2-like transcription factor involved in regulating gene expression during nitrogen limitation in fungi?

The upstream sequences of all published lignin peroxidase and manganese peroxidase genomic clones from Phanerochaete chrysosporium were analyzed. This analysis revealed the presence of putative activator protein-2 (AP-2) recognition sequences in 11 of 15 lignin peroxidase genes. The lignin peroxidase clone GLG6 and the manganese peroxidase gene (mnp-1) have two copies of putative AP-2 sequence in the upstream region. Interestingly, the lignin peroxidase gene VLG4 of another white rot fungus, Trametes versicolor, and the nit-2 gene of Neurospora crassa also contain putative AP-2-binding sequences. Since all of these genes are regulated by nutrient nitrogen, I hypothesize that an AP-2-like transcription factor may be involved in inducing gene expression during nitrogen limitation in fungi.

Base Sequence↗
PubMed1994

A simple method that uses differential staining and light microscopy to assess the selectivity of wood delignification by white rot fungi.

CRYOSTAT MICROTOME SECTIONS OF BIRCH WOOD DEGRADED BY WHITE ROT FUNGI WERE EXAMINED BY LIGHT MICROSCOPY AFTER TREATMENT WITH TWO STAINS: astra-blue, which stains cellulose blue only in the absence of lignin, and safranin, which stains lignin regardless of whether cellulose is present. The method provided a simple and reliable screening procedure that distinguishes between fungi that cause decay by selectively removing lignin and those that degrade both cellulose and lignin simultaneously. Moreover, morphological characteristics specific to selective delignification were revealed.

Journal Article↗
PubMed1994

Compositional Changes in Compost during Composting and Growth of Agaricus bisporus.

Samples from conventional compost taken at various stages of composting and mushroom (Agaricus bisporus) growth were analyzed for changes in 80% ethanol and water extracts, monosaccharides in acid hydrolysates of polysaccharides, lignin concentration, and lignin structural features. Variable amounts of extraneous inorganic solids in the form of fine sandy particles were removed by sedimentation of the samples in a carbon tetrachloride-dibromomethane mixture. During composting, about two-thirds of the initial wall polysaccharides were consumed by compost microorganisms, and only 17% of the total polysaccharides were used during mushroom production. The relative lignin content of composts as measured by the acetyl bromide procedure increased, both during composting and mushroom growth, and the chemical structure of lignin was altered by condensation and oxidation reactions.

Journal Article↗
PubMed1996

Purification and Characterization of Cellobiose Dehydrogenases from the White Rot Fungus Trametes versicolor.

The white rot fungus Trametes versicolor degrades lignocellulosic material at least in part by oxidizing the lignin via a number of secreted oxidative and peroxidative enzymes. An extracellular reductive enzyme, cellobiose dehydrogenase (CDH), oxidizes cellobiose and reduces insoluble Mn(IV)O(inf2), commonly found as dark deposits in decaying wood, to form Mn(III), a powerful lignin-oxidizing agent. CDH also reduces ortho-quinones and produces sugar acids which can promote manganese peroxidase and therefore ligninolytic activity. To better understand the role of CDH in lignin degradation, proteins exhibiting cellobiose-dependent quinone-reducing activity were isolated and purified from cultures of T. versicolor. Two distinct proteins were isolated; the proteins had apparent molecular weights of 97,000 and 81,000 and isoelectric points of 4.2 and 6.4, respectively. The larger CDH (CDH 4.2) contained both flavin and heme cofactors, whereas the smaller contained only a flavin (CDH 6.4). These CDH enzymes were rapidly reduced by cellobiose and lactose and somewhat more slowly by cellulose and certain cello-oligosaccharides. Both glycoproteins were able to reduce a very wide range of quinones and organic radical species but differed in their ability to reduce metal ion complexes. Temperature and pH optima for CDH 4.2 were affected by the reduced substrate. Although CDH 4.2 showed rather high substrate specificity among the ortho-quinones, it could also rapidly reduce a structurally very diverse collection of other species, from negatively charged triiodide ions to positively charged hexaquo ferric ions. CDH 6.4 showed a higher K(infm) and a lower V(infmax) and turnover number than did CDH 4.2 for all substrates tested. Furthermore, CDH 6.4 did not reduce the transition metals Fe(III), Cu(II), and Mn(III) at concentrations likely to be physiologically relevant, while CDH 4.2 was able to rapidly reduce even very low concentrations of these ions. The reduction of Fe(III) and Cu(II) by CDH 4.2 may be important in sustaining a Fenton's-type reaction, which produces hydroxyl radicals that can cleave both lignin and cellulose. Unlike the CDH proteins from Phanerochaete chrysosporium, CDH 4.2 and CDH 6.4 are unable to produce hydrogen peroxide.

Journal Article↗
PubMed2000

A homokaryotic derivative of a Phanerochaete chrysosporium strain and its use in genomic analysis of repetitive elements.

Analysis of complex gene families in the lignin-degrading basidiomycete Phanerochaete chrysosporium has been hampered by the dikaryotic nuclear condition. To facilitate genetic investigations in P. chrysosporium strain BKM-F-1767, we isolated a homokaryon from regenerated protoplasts. The nuclear condition was established by PCR amplification of five unlinked genes followed by probing with allele-specific oligonucleotides. Under standard nitrogen-limited culture conditions, lignin peroxidase, manganese peroxidase, and glyoxal oxidase activities of the homokaryon were equivalent to those of the parental dikaryon. We used the homokaryon to determine the genomic organization and to assess transcriptional effects of a family of repetitive elements. Previous studies had identified an insertional mutation, Pce1, within lignin peroxidase allele lipI2. The element resembled nonautonomous class II transposons and was present in multiple copies in strain BKM-F-1767. In the present study, three additional copies of the Pce1-like element were cloned and sequenced. The distribution of elements was nonrandom; all localized to the same 3.7-Mb chromosome, as assessed by segregation analysis and Southern blot analysis of the homokaryon. Reverse transcription-PCR (RT-PCR) showed that Pce1 was not spliced from the lipI2 transcript in either the homokaryon or the parental dikaryon. However, both strains had equivalent lignin peroxidase activity, suggesting that some lip genes may be redundant.

Chromosome Mapping↗
PubMed2005

Application of sequential aqueous steam treatments to the fractionation of softwood.

The FIRST (Feedstock Impregnation and Rapid Steam Treatment) approach was used in this study to isolate extractives, hemicellulose, lignin, fibers, and cellulosic fines of softwood. With hydrolysis and fermentation of the hemicellulose and cellulosic fines fractions, this approach produces four co-products: extractives, cellulose, lignin, and ethanol. The first unit operation uses aqueous/alcohol to remove and recover the extractive rich fraction. The second unit operation uses steam treatment to destructure the matrix and solubilize a large fraction of the hemicelluloses. The third unit operation uses alkaline delignification to dissolve a lignin fraction. The fourth unit operation uses the refining process to separate fibers from cellulosic fines. The fibers are bleached. The yields of lignin and bleached cellulose were about 20.0 kg and 38.3 kg out of 100 kg initial dry pine, respectively. The recovered hemicelluloses were 23.3 kg (containing 16.1 kg hexoses and 5.0 kg pentoses) and the cellulose fines derived hexoses amounted to 3.4 kg out of 100 kg initial dry pine. When the two liquors containing the hemicellulose sugars and the cellulose fines-derived hexoses were fermented for ethanol production, an ethanol yield of 6.8 kg was obtained.

Cellulose↗
PubMed2006

Updates on softwood-to-ethanol process development.

Softwoods are generally considered to be one of the most difficult lignocellulosic feedstocks to hydrolyze to sugars for fermentation, primarily owing to the nature and amount of lignin. If the inhibitory effect of lignin can be significantly reduced, softwoods may become a more useful feedstock for the bioconversion processes. Moreover, strategies developed to reduce problems with softwood lignin may also provide a means to enhance the processing of other lignocellulosic substrates. The Forest Products Biotechnology Group at the University of British Columbia has been developing softwood-to-ethanol processes with SO2-catalyzed steam explosion and ethanol organosolv pretreatments. Lignin from the steam explosion process has relatively low reactivity and, consequently, low product value, compared with the high-value coproduct that can be obtained through organosolv. The technical and economic challenges of both processes are presented, together with suggestions for future process development.

Biomass↗
PubMed2000

Sunlight persistence and rainfastness of spray-dried formulations of baculovirus isolated from Anagrapha falcifera (Lepidoptera: Noctuidae).

Nuclear polyhedrosis viruses such as the one isolated from the celery looper, Anagrapha falcifera (Kirby) (AfMNPV), have the potential to be successful bioinsecticides if improved formulations can prevent rapid loss of insecticidal activity from environmental conditions such as sunlight and rainfall. We tested 16 spray-dried formulations of AfMNPV to determine the effect of different ingredients (e.g., lignin, corn flour, and so on) on insecticidal activity after simulated rain and simulated sunlight (at Peoria, IL) and natural sunlight exposures (at Tifton, GA). The most effective formulation contained pregelatinized corn flour and potassium lignate, which retained more than half of its original activity after 5 cm of simulated rain, and almost full activity after 8 h of simulated sunlight. In Georgia, formulations made with and without lignin were compared for persistence of insecticidal activity when exposed to natural sunlight. In addition, the effect of fluorescent brighteners as formulation components and spray tank additives was tested. Results showed that the formulations with lignin had more insecticidal activity remaining after sunlight exposure than formulations without lignin. The inclusion of brighteners in the formulation did not improve initial activity or virus persistence. However, a 1% tank mix significantly enhanced activity and improved persistence. Scanning electron micrographs revealed discreet particles, and transmission electron micrographs showed virus embedded within microgranules. Results demonstrated that formulations made with natural ingredients could improve persistence of virus-based biopesticides.

Animals↗
PubMed1991

Isolation and chemical analyses of nonfermented fiber fractions of oat hulls and cottonseed hulls.

The purpose of this study was to isolate, using both in situ and in vivo methodology, the nonfermented fiber fraction of oat hulls (OH) and cottonseed hulls (CSH) and to compare the concentrations of alkali-labile phenolic monomers, nitrobenzene oxidizable phenolic monomers, and neutral monosaccharides, as well as the cross polarization/magic angle spinning (CP/MAS) carbon-13 (13C) nuclear magnetic resonance (NMR) spectra, of the nonfermented fraction with the original OH or CSH. The in situ isolation procedure involved a 30-h ruminal pretreatment and an 8-h acid:pepsin pretreatment followed by 1 to 7 additional days of incubation in the rumen. Fractions not fermented in vivo were isolated from duodena, ileal, and fecal material obtained from a site and extent of digestion trial in which these byproducts were fed to sheep at 80% of the diet (as-fed basis) and they represented the sole source of dietary fiber. Based on nonfermented fraction composition, both in situ and in vivo, all components analyzed were degraded to some extent. Also, all components present in original byproduct material were present in both the in situ and in vivo nonfermented fractions. Based on NMR analysis, cellulose crystallinity did not change during either long-term in situ or in vivo fermentation. However, CSH cellulose was more crystalline than that of OH. The ADL content of OH and CSH was 6.1% and 19.4%, respectively, and very little (15%) of the ADL disappeared during either in situ or in vivo fermentation. Much of the p-coumaric and ferulic acid of OH, associated with the cell wall matrix as lignin-carbohydrate and phenolic-carbohydrate complexes, was recovered in the fermented fractions. Data are interpreted to indicate that lignin encrustation and cellulose crystallinity are factors affecting CSH fermentation. Lignin encrustation and the presence of lignin-carbohydrate/phenolic-carbohydrate complexes are factors that inhibit OH fermentation.

Animal Feed↗