Lignocellulose Biodegradation Research Articles

Screening of Phytophagous and Xylophagous Insects Guts Microbiota Abilities to Degrade Lignocellulose in Bioreactor.

Microbial consortia producing specific enzymatic cocktails are present in the gut of phytophagous and xylophagous insects; they are known to be the most efficient ecosystems to degrade lignocellulose. Here, the ability of these consortia to degrade ex vivo lignocellulosic biomass in anaerobic bioreactors was characterized in term of bioprocess performances, enzymatic activities and bacterial community structure. In a preliminary screening, guts of Ergates faber (beetle), Potosia cuprea (chafer), Gromphadorrhina portentosa (cockroach), Locusta migratoria (locust), and Gryllus bimaculatus (cricket) were inoculated in anaerobic batch reactors, in presence of grounded wheat straw at neutral pH. A short duration fermentation of less than 8 days was observed and was related to a drop of pH from 7 to below 4.5, leading to an interruption of gas and metabolites production. Consistently, a maximum of 180 mgeq.COD of metabolites accumulated in the medium, which was related to a low degradation of the lignocellulosic biomass, with a maximum of 5 and 2.2% observed for chafer and locust gut consortia. The initial cell-bound and extracellular enzyme activities, i.e., xylanase and β-endoglucanase, were similar to values observed in the literature. Wheat straw fermentation in bioreactors leads to an increase of cell-bounded enzyme activities, with an increase of 145% for cockroach xylanase activity. Bacterial community structures were insect dependent and mainly composed of Clostridia, Bacteroidia and Gammaproteobacteria. Improvement of lignocellulose biodegradation was operated in successive batch mode at pH 8 using the most interesting consortia, i.e., locust, cockroaches and chafer gut consortia. In these conditions, lignocellulose degradation increased significantly: 8.4, 10.5, and 21.0% of the initial COD were degraded for chafer, cockroaches and locusts, respectively in 15 days. Consistently, xylanase activity tripled for the three consortia, attesting the improvement of the process. Bacteroidia was the major bacterial class represented in the bacterial community for all consortia, followed by Clostridia and Gammaproteobacteria classes. This work demonstrates the possibility to maintain apart of insect gut biological activity ex vivo and shows that lignocellulose biodegradation can be improved by using a biomimetic approach. These results bring new insights for the optimization of lignocellulose degradation in bioreactors.

Biodegradation of lignin by Pseudomonas sp. Q18 and the characterization of a novel bacterial DyP-type peroxidase.

Lignin valorization can be obtained through cleavage of selected bonds by microbial enzymes, in which lignin is segregated from cellulose and hemicellulose and abundant phenolic compounds can be provided. In this study, Pseudomonas sp. Q18, previously isolated from rotten wood in China, was used to degrade alkali lignin and raw lignocellulosic material. Gel-permeation chromatography, field-emission scanning electron microscope, and GC-MS were combined to investigate the degradation process. The GC-MS results revealed that the quantities of aromatic compounds with phenol ring from lignin increased significantly after incubation with Pseudomonas sp. Q18, which indicated the degradation of lignin. According to the lignin-derived metabolite analysis, it was proposed that a DyP-type peroxidase (PmDyP) might exist in strain Q18. Thereafter, the gene of PmDyP was cloned and expressed, after which the recombinant PmDyP was purified and the enzymatic kinetics of PmDyP were assayed. According to results, PmDyP showed promising characteristics for lignocellulosic biodegradation in biorefinery.

Penicillium purpurogenum Produces a Set of Endoxylanases: Identification, Heterologous Expression, and Characterization of a Fourth Xylanase, XynD, a Novel Enzyme Belonging to Glycoside Hydrolase Family 10.

The fungus Penicillium purpurogenum grows on a variety of natural carbon sources and secretes a large number of enzymes which degrade the polysaccharides present in lignocellulose. In this work, the gene coding for a novel endoxylanase has been identified in the genome of the fungus. This gene (xynd) possesses four introns. The cDNA has been expressed in Pichia pastoris and characterized. The enzyme, XynD, belongs to family 10 of the glycoside hydrolases. Mature XynD has a calculated molecular weight of 40,997. It consists of 387 amino acid residues with an N-terminal catalytic module, a linker rich in ser and thr residues, and a C-terminal family 1 carbohydrate-binding module. XynD shows the highest identity (97%) to a putative endoxylanase from Penicillium subrubescens but its highest identity to a biochemically characterized xylanase (XYND from Penicillium funiculosum) is only 68%. The enzyme has a temperature optimum of 60°C, and it is highly stable in its pH optimum range of 6.5-8.5. XynD is the fourth biochemically characterized endoxylanase from P. purpurogenum, confirming the rich potential of this fungus for lignocellulose biodegradation. XynD, due to its wide pH optimum and stability, may be a useful enzyme in biotechnological procedures related to this biodegradation process.

An Effective Modification with Mild Alkali Pretreatment for Enhancing the Biodegradation of Wheat Straw by Pycnoporus sanguineus NFZH-1

A delignification pretreatment is important for enhancing lignocellulose biodegradation. Alkali pretreatment is a promising approach. Fiber morphology, alkaline nitrobenzene oxidation, and ozonation were used to characterize the wheat straw modified by mild alkali pretreatment (2% sodium hydroxide (NaOH) at 121 °C for 30 min), and for studying the advantageous performance by Pycnoporus sanguineus NFZH-1 in the aspects of lignin and carbohydrate biodegradation. The results indicated a powerful and selective delignification in the mild alkali pretreatment process. The relative contents of the G unit and the T form both decreased with mild alkali pretreatment. Meanwhile, epicuticular wax removal and increased porosity was observed in the fibrous tissue of alkali-treated wheat straw. Thus, the biodegradation of the Klason lignin in alkali-treated wheat straw was clearly enhanced and reached 41.4% during the following 10 days of fermentation with P. sanguineus NFZH-1. In addition, the modification of fiber tissue with a mild alkali pretreatment enhanced the biodegradation of xylan. The biodegradation of the chemical constituents of the wheat straw was enhanced by the effective modification with a mild alkali pretreatment. The enhanced biodegradation will be helpful for improving the efficiency of straw return.

Lignocellulose biodegradation in the biodrying process of sewage sludge and sawdust

ABSTRACTLignocellulose degradation is important when applying biodrying treatment to sewage sludge intended for land use. This study investigated the lignocellulose degradation in the biodrying of sewage sludge and sawdust. The experiment analyzed lignocellulose content, lignocellulase activity, humic substances, and fungal communities. After biodrying, lignin, cellulose, and hemicellulose degradation rates were 48.4, 38.8, and 45.0%, respectively. Carboxymethyl cellulase, lignin peroxidase, and xylanase played key roles. During the thermophilic phase, more than 80% of the microorganisms in the sample contributing to lignocellulose degradation were Ascomycota. The lignocellulose degradation and a rate of increase in humic acid/fulvic acid of 380% benefit land use of biodrying product.

An aldonolactonase AltA from Penicillium oxalicum mitigates the inhibition of β-glucosidase during lignocellulose biodegradation.

Efficient deconstruction of lignocellulose is achieved by the synergistic action of various hydrolytic and oxidative enzymes. However, the aldonolactones generated by oxidative enzymes have inhibitory effects on some cellulolytic enzymes. In this work, D-glucono-1,5-lactone was shown to have a much stronger inhibitory effect than D-glucose and D-gluconate on β-glucosidase, a vital enzyme during cellulose degradation. AltA, a secreted enzyme from Penicillium oxalicum, was identified as an aldonolactonase which can catalyze the hydrolysis of D-glucono-1,5-lactone to D-gluconic acid. In the course of lignocellulose saccharification conducted by cellulases from P. oxalicum or Trichoderma reesei, supplementation of AltA was able to relieve the decrease of β-glucosidase activity obviously with a stimulation of glucose yield. This boosting effect disappeared when sodium azide and ethylenediaminetetraacetic acid (EDTA) were added to the saccharification system to inhibit the activities of oxidative enzymes. In summary, we describe the first heterologous expression of a fungal secreted aldonolactonase and its application as an efficient supplement of cellulolytic enzyme system for lignocellulose biodegradation.

Lignocellulose-degrading enzymes, free-radical transformations during composting of lignocellulosic waste and biothermal phases in small-scale reactors.

Environmentally friendly strategies of waste management are both part of legal solutions currently in place and a focus of interest worldwide. Large-scale composting plants are set up across various regions while home composting is becoming increasingly popular. A variety of microbial groups are successively at work during composting and enzymatic activities detected in the composting mass fluctuate accordingly. Changes in the activities of oxidoreductases and hydrolases, i.e. glucose oxidase, horseradish peroxidase, lignin peroxidase, laccase, xylanase, superoxide dismutase and keratinase, low-molecular weight compounds, i.e. methoxyphenolic and hydroxyphenolic compounds, and the relative level of superoxide radicals and glucose were determined periodically in water extracts of composts to investigate the process of biochemical transformations of ligninocellulose in relation to biothermal phases and to identify a potential priming effect in two composts containing different ratios of lignocellulosic waste and chicken feathers. Composting was conducted for 30weeks. An important aim of the study was to demonstrate that a positive priming effect was induced during composting of a variety of lignocellulosic waste types using native keratin (chicken feathers) as a source of N. The effect was more evident in compost containing grass, which was related to a more rapid depletion of easily available sources of C and energy (glucose) during composting. Ligninolytic enzymes known to biodegrade recalcitrant organic matter were induced in subsequent biothermal phases of composting. Compost I enriched with grass (pine bark, grass, sawdust and chicken feathers) exhibited a higher enzymatic activity than compost II which did not contain any grass but which had a greater number of hardly-degradable components (pine bark, wheat straw, sawdust, chicken feathers). Similar observations were made for the concentrations of low-molecular weight compounds. The enzymes activities and concentration of low-molecular weight compounds listed above can be used to estimate the biodegradation of lignocellulose during composting.

Metagenomic and metaproteomic analyses of a corn stover-adapted microbial consortium EMSD5 reveal its taxonomic and enzymatic basis for degrading lignocellulose.

BackgroundMicrobial consortia represent promising candidates for aiding in the development of plant biomass conversion strategies for biofuel production. However, the interaction between different community members and the dynamics of enzyme complements during the lignocellulose deconstruction process remain poorly understood. We present here a comprehensive study on the community structure and enzyme systems of a lignocellulolytic microbial consortium EMSD5 during growth on corn stover, using metagenome sequencing in combination with quantitative metaproteomics.ResultsThe taxonomic affiliation of the metagenomic data showed that EMSD5 was primarily composed of members from the phyla Proteobacteria, Firmicutes and Bacteroidetes. The carbohydrate-active enzyme (CAZyme) annotation revealed that representatives of Firmicutes encoded a broad array of enzymes responsible for hemicellulose and cellulose deconstruction. Extracellular metaproteome analysis further pinpointed the specific role and synergistic interaction of Firmicutes populations in plant polysaccharide breakdown. In particular, a wide range of xylan degradation-related enzymes, including xylanases, β-xylosidases, α-l-arabinofuranosidases, α-glucuronidases and acetyl xylan esterases, were secreted by diverse members from Firmicutes during growth on corn stover. Using label-free quantitative proteomics, we identified the differential secretion pattern of a core subset of enzymes, including xylanases and cellulases with multiple carbohydrate-binding modules (CBMs). In addition, analysis of the coordinate expression patterns indicated that transport proteins and hypothetical proteins may play a role in bacteria processing lignocellulose. Moreover, enzyme preparation from EMSD5 demonstrated synergistic activities in the hydrolysis of pretreated corn stover by commercial cellulases from Trichoderma reesei.ConclusionsThese results demonstrate that the corn stover-adapted microbial consortium EMSD5 harbors a variety of lignocellulolytic anaerobic bacteria and degradative enzymes, especially those implicated in hemicellulose decomposition. The data in this study highlight the pivotal role and cooperative relationship of Firmicutes members in the biodegradation of plant lignocellulose by EMSD5. The differential expression patterns of enzymes reveal the strategy of sequential lignocellulose deconstruction by EMSD5. Our findings provide insights into the mechanism by which consortium members orchestrate their array of enzymes to degrade complex lignocellulosic biomass.Electronic supplementary materialThe online version of this article (doi:10.1186/s13068-016-0658-z) contains supplementary material, which is available to authorized users.

Construction and Characterization of a Cellulolytic Consortium Enriched from the Hindgut of Holotrichia parallela Larvae.

Degradation of rice straw by cooperative microbial activities is at present the most attractive alternative to fuels and provides a basis for biomass conversion. The use of microbial consortia in the biodegradation of lignocelluloses could reduce problems such as incomplete synergistic enzymes, end-product inhibition, and so on. In this study, a cellulolytic microbial consortium was enriched from the hindgut of Holotrichia parallela larvae via continuous subcultivation (20 subcultures in total) under static conditions. The degradation ratio for rice straw was about 83.1% after three days of cultivation, indicating its strong cellulolytic activity. The diversity analysis results showed that the bacterial diversity and richness decreased during the consortium enrichment process, and the consortium enrichment process could lead to a significant enrichment of phyla Proteobacteria and Spirochaetes, classes Clostridia, Epsilonproteobacteria, and Betaproteobacteria, and genera Arcobacter, Treponema, Comamonas, and Clostridium. Some of these are well known as typical cellulolytic and hemicellulolytic microorganisms. Our results revealed that the microbial consortium identified herein is a potential candidate for use in the degradation of waste lignocellulosic biomass and further highlights the hindgut of the larvae as a reservoir of extensive and specific cellulolytic and hemicellulolytic microbes.

Isolation, identification and fibrolytic characteristics of rumen fungi grown with indigenous methanogen from yaks (Bos grunniens) grazing on the Qinghai-Tibetan Plateau.

To obtain co-cultures of anaerobic fungi and their indigenously associated methanogens from the rumen of yaks grazing on the Qinghai-Tibetan Plateau and investigate their morphology features and ability to degrade lignocellulose. Twenty fungus-methanogen co-cultures were obtained by Hungate roll-tube technique. The fungi were identified as Orpinomyces, Neocallimastix and Piromyces genera based on the morphological characteristics and internal transcribed spacer 1 sequences analysis. All methanogens were identified as Methanobrevibacter sp. by 16S rRNA gene sequencing. There were four types of co-cultures: Neocallimastix with Methanobrevibacter ruminantium, Orpinomyces with M.ruminantium, Orpinomyces with Methanobrevibacter millerae and Piromyces with M.ruminantium among 20 co-cultures. In vitro studies with wheat straw as substrate showed that the Neocallimastix with M.ruminantium co-cultures and Piromyces with M.ruminantium co-cultures exhibited higher xylanase, filter paper cellulase (FPase), ferulic acid esterase, acetyl esterase activities, invitro dry matter digestibility, gas, CH4 , acetate production, ferulic acid and p-coumaric acid releases. The Neocallimastix frontalis Yak16 with M.ruminantium co-culture presented the strongest lignocellulose degradation ability among 20 co-cultures. Twenty fungus-methanogen co-cultures were obtained from the rumen of grazing yaks. The N.frontalis with M.ruminantium co-cultures were highly effective combination for developing a fermentative system that bioconverts lignocellulose to high activity fibre-degrading enzyme, CH4 and acetate. The N.frontalis with M.ruminantium co-cultures from yaks grazing on the Qinghai-Tibetan Plateau present great potential in lignocellulose biodegradation industry.

Metagenomic analysis of microbial consortia enriched from compost: new insights into the role of Actinobacteria in lignocellulose decomposition.

BackgroundCompost habitats sustain a vast ensemble of microbes specializing in the degradation of lignocellulosic plant materials and are thus important both for their roles in the global carbon cycle and as potential sources of biochemical catalysts for advanced biofuels production. Studies have revealed substantial diversity in compost microbiomes, yet how this diversity relates to functions and even to the genes encoding lignocellulolytic enzymes remains obscure. Here, we used a metagenomic analysis of the rice straw-adapted (RSA) microbial consortia enriched from compost ecosystems to decipher the systematic and functional contexts within such a distinctive microbiome.ResultsAnalyses of the 16S pyrotag library and 5 Gbp of metagenomic sequence showed that the phylum Actinobacteria was the predominant group among the Bacteria in the RSA consortia, followed by Proteobacteria, Firmicutes, Chloroflexi, and Bacteroidetes. The CAZymes profile revealed that CAZyme genes in the RSA consortia were also widely distributed within these bacterial phyla. Strikingly, about 46.1 % of CAZyme genes were from actinomycetal communities, which harbored a substantially expanded catalog of the cellobiohydrolase, β-glucosidase, acetyl xylan esterase, arabinofuranosidase, pectin lyase, and ligninase genes. Among these communities, a variety of previously unrecognized species was found, which reveals a greater ecological functional diversity of thermophilic Actinobacteria than previously assumed.ConclusionThese data underline the pivotal role of thermophilic Actinobacteria in lignocellulose biodegradation processes in the compost habitat. Besides revealing a new benchmark for microbial enzymatic deconstruction of lignocelluloses, the results suggest that actinomycetes found in compost ecosystems are potential candidates for mining efficient lignocellulosic enzymes in the biofuel industry.Electronic supplementary materialThe online version of this article (doi:10.1186/s13068-016-0440-2) contains supplementary material, which is available to authorized users.

Syntrophic microbial system for ex-situ degradation of paddy straw at low temperature under controlled and natural environment

The syntrophic microbial application for lignocellulosic biodegradation and subsequent transformation into compost provides an alternative strategy against burning and disposing post harvested agricultural biomass which is of vital importance in agriculture used as compost. Biodegradation process is hindered during winter season, as the microorganisms involved in lignocellulose biodegradation slows down their metabolism due to unfavourable growth conditions at low temperatures. In order to intensify the composting process at low temperature, psychrotrophic microbes were isolated and characterized for lignocellulosic hydrolytic potential specifically at low temperatures. Among the isolated microbes, four efficient lignocellulolytic psychrotrophic microbes (Eupenicillium crustaceum, Paceliomyces sp., Bacillus atropheus and Bacillus sp.) and commercial fungal consortia (Aspergillus awamori, Aspergillus nidulans, Trichoderma viride and Phanerochaete chrysosporium) were used in present study. It was found that psychrotrophic microbes along with the commercial fungal consortium enhanced the composting process at low temperature. These psychrotrophic and mesophilic microbial consortium can be used for degradation of agri-residues and conversion to a value added product like compost, which helps in enhancing soil fertility and decreasing environmental pollution caused by burning of agrowastes. This is the first report for biodegradation of paddy straw by psychrotrophic microbes at low temperatures.

Expression of feruloyl esterase A from Aspergillus terreus and its application in biomass degradation

Feruloyl esterases (FAEs) are key enzymes involved in the complete biodegradation of lignocelluloses, which could hydrolyze the ester bonds between hemicellulose and lignin. The coding sequence of a feruloyl esterase A (AtFaeA) was cloned from Aspergillus terreus and the recombinant AtFaeA was constitutively expressed in Pichia pastoris. The SDS–PAGE analysis of purified AtFaeA showed two protein bands owing to the different extent of glycosylation, and the recombinant AtFaeA had an optimum temperature of 50°C and an optimum pH of 5.0. The substrate utilization and primary sequence identity of AtFaeA demonstrated that it is a type-A feruloyl esterase. The hydrolysis of corn stalk and corncob by xylanase from Aspergillus niger could be significantly improved in concert with recombinant AfFaeA.

Direct three-dimensional characterization and multiscale visualization of wheat straw deconstruction by white rot fungus.

Microbial degradation of lignocellulose for resource and energy recovery has received increasing interest. Despite its obvious importance, the mechanism behind the biodegradation, especially the changes of morphological structure and surface characteristics, has not been fully understood. Here, we used three-dimensional (3D) characterization and multiscale visualization methods, in combination with chemical compositional analyses, to elucidate the degradation process of wheat straw by a white rot fungus, Phanerochaete chrysosporium. It was found that the fungal attack initiated from stomata. Lignin of the straw decayed in both size and quantity, and heterogeneity in the biodegradation was observed. After treatment with the fungus, the straw surface turned from hydrophobic to hydrophilic, and the adhesion of the straw surface increased in the fungal degradation. The morphology of the straw outer layer became heterogeneous and loose with the formation of many holes with various sizes. The wasp-tunnels-like structure of the collenchyma and parenchyma of the straw as well as the fungal hyphae interspersed inside the straw structure were clearly visualized in the 3D reconstruction structure. This work offers a new insight into the mechanism of lignocellulose biodegradation and demonstrates that multiscale visualization methods could be a useful tool to explore such complex processes.

Phanerochaete chrysosporium inoculation shapes the indigenous fungal communities during agricultural waste composting.

Inoculation with exogenous white-rot fungi has been proven to be an efficient method to promote lignocellulose biodegradation during agricultural waste composting. Indigenous fungal communities, the most important organisms responsible for mineralization and decomposition of lignocellulosic materials in composts, can be affected by sample properties and other biotic factors. This research was conducted to determine the effects of the Phanerochaete chrysosporium inoculation on the indigenous fungal communities during agricultural waste composting. Fungal communities in samples with different inoculation regimes were investigated by sequencing and quantitative PCR. Results showed that P. chrysosporium inoculants produced significant negative effects on the indigenous fungal community abundance during the thermophilic stage. Samples inoculated during Phase II contained higher proportion of Acremonium chrysogenum and Galactomyces geotrichum, while those non-inoculated samples were dominated by Coprinopsis cinerea and Scytalidium thermophilum. Moreover, the indigenous fungal community abundance was significantly correlated with the C/N ratio, water soluble carbon and moisture content (P < 0.05). Redundancy analysis indicated that the most variation in distribution of indigenous fungal community structure was statistically explained by nitrate, C/N ratio, and moisture content, factors which solely explained 29.6 % (F = 30.316, P = 0.002), 25.6 % (F = 26.191, P = 0.002) and 10.0 % (F = 10.249, P = 0.002) of the variation in the indigenous fungal community structure, respectively.

A Cost-effective Integrated Process to Convert Sweet Sorghum Stalks into Biofuels

Biofuel is a renewable and sustainable energy as an substitute of fossil fuel. In China, the key challenge to develop biofuels is how to balance the competition of food and bioenergy and supply a sustainable feedstock. Sweet sorghum is highlighted as a multiple platform plant which can supply grain, sugar, cellulose and feed. In addition, sweet sorghum has so good tolerance of drought and sterilize that it can grow on marginal land. However, the loose stalk pith of sweet sorghum results in the infeasibility of liquid fermentation technology due to the considerably high energy consumption.In present research, an integrated process combined advanced solid-state fermentation technology (ASSF) and alkaline pretreatment was presented in this work. Soluble sugars in sweet sorghum stalks were firstly converted into ethanol by ASSF using crushed stalks directly. Then, the operation combining ethanol distillation and alkaline pretreatment was performed in one distillation-reactor simultaneously. The process was optimized according to the yield of sugar-ethanol and amounts of monosaccharide released from SSB. In our novel process, energy consumption of mechanically squeeze and pretreatment of SSB was avoided. Meanwhile, the recalcitrance of lignocellulose was destructed and the biodegradation of lignocellulose into chemical products is feasible to achieve. Cellulosic ethanol as a model product was studied by using this novel integrated process. The mass balance of the overall process was calculated, and 91.9kg was achieved from one tonne of fresh sweet sorghum stalk. Energy consumption for raw materials preparation and pretreatment were reduced or avoided in our process. To produce 1 tonne of ethanol, the energy input in this process was 12,481.2MJ/tonne, while the energy input in other cellulosic ethanol processes is from 17,430 to 33,330MJ/tonne.Based on this technology, the recalcitrance of lignocellulose was destructed via a cost-efficient process and structural carbohydrates in sweet sorghum stalks were hydrolysed into fermentable sugars. Bioconversion of fermentable sugars released from sweet sorghum bagasse into different products except ethanol, such as butanol, biogas, and chemicals was feasible to operate under low energy-consumption conditions. So it is considered as a promising process to produce biofuels at commercial scale.

The influence of lignin–carbohydrate complexes on the cellulase-mediated saccharification I: Transgenic black cottonwood (western balsam poplar, California poplar) P. trichocarpa including the xylan down-regulated and the lignin down-regulated lines

The influence of the putative lignin–carbohydrate complexes (LCCs) on enzymatic saccharification was elucidated for the first time by examining two groups of transgenic black cottonwood (P. trichocarpa) comprised of the lignin down-regulated and the xylan down-regulated lines. Any adventitious contaminants that could affect the characterization of LCCs and the enzymatic saccharification were removed by performing a thorough extraction on the samples. The crude milled wood lignin was subsequently isolated from which the phenyl glycoside, benzyl ether and γ-ester linkages representative of the LCCs were identified and quantified with the combination of 13C and 1H–13C Heteronuclear Single Quantum Coherence (HSQC) NMR. The result indicated that the samples showed different levels of the three LCC linkages, depending on the xylan and/or lignin content. The correlation between the LCCs and enzymatic saccharification nearly conclusively demonstrated that the LCCs accounting for the recalcitrance of lignocellulosic biodegradation.

Particle Diameter and Nutrient Related Studies of Anaerobic Biodegradation of Lignocellulose from Corn Stalks in Biogas Production for Sustainable Energy Development

Unextracted lignocellulose from corn stalks was investigated for its anaerobic biodegradability at 38 oC using mixed micro organisms harnessed directly from the air. The effects of particle diameter and certain nutrients on biodegradability were investigated. The highest biogas yield was observed for ? 1.0 mm particle diameter size, followed by ? 2.0 mm particle diameter and then ? 3.0 mm particle diameter. Potato dextrose agar (PDA) and urea were found to increase biogas yield when in low concentrations. The combination of PDA and urea in low concentrations is a better nutrient than either PDA or urea alone.

The influence of lignin–carbohydrate complexes on the cellulase-mediated saccharification II: Transgenic hybrid poplars (Populus nigra L. and Populus maximowiczii A.)

Twelve transgenic hybrid poplars (Populus nigra L. and Populus maximowiczii A.) were used to demonstrate the influence of the lignin–carbohydrate complexes (LCCs) on enzymatic saccharification. The samples have different levels of the syringaldehyde (S) to vanillin (V) ratio from 0.1 to 2.6 and the lignin content from 10.5% to 24.3%, compared to the control (the S/V ratio 1.7 and the lignin content 22.0%). Any adventitious contaminants that could affect the final enzymatic saccharification were removed by performing thorough extraction on the samples. The crude milled wood lignins were subsequently isolated from which the phenyl glycoside, benzyl ether and γ-ester linkages representative of the LCC were identified and quantified by 13C and 1H–13C HSQC NMR. It was found that the samples showed different levels of the three LCC linkages, depending on the lignin content and/or the S/V ratio. The correlation between the LCCs and enzymatic saccharification nearly conclusively demonstrated that the LCCs accounted for the recalcitrance of lignocellulosic biodegradation.

Multidimensional NMR analysis reveals truncated lignin structures in wood decayed by the brown rot basidiomycete Postia placenta

Lignocellulose biodegradation, an essential step in terrestrial carbon cycling, generally involves removal of the recalcitrant lignin barrier that otherwise prevents infiltration by microbial polysaccharide hydrolases. However, fungi that cause brown rot of wood, a major route for biomass recycling in coniferous forests, utilize wood polysaccharides efficiently while removing little of the lignin. The mechanism by which these basidiomycetes breach the lignin remains unclear. We used recently developed methods for solubilization and multidimensional (1) H-(13) C solution-state NMR spectroscopy of ball-milled lignocellulose to analyse aspen wood degraded by Postia placenta. The results showed that decay decreased the content of the principal arylglycerol-β-aryl ether interunit linkage in the lignin by more than half, while increasing the frequency of several truncated lignin structures roughly fourfold over the level found in sound aspen. These new end-groups, consisting of benzaldehydes, benzoic acids and phenylglycerols, accounted for 6-7% of all original lignin subunits. Our results provide evidence that brown rot by P. placenta results in significant ligninolysis, which might enable infiltration of the wood by polysaccharide hydrolases even though the partially degraded lignin remains in situ. Recent work has revealed that the P. placenta genome encodes no ligninolytic peroxidases, but has also shown that this fungus produces an extracellular Fenton system. It is accordingly likely that P. placenta employs electrophilic reactive oxygen species such as hydroxyl radicals to disrupt lignin in wood.