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 ¹⁴C-[lignin]-lignocellulose and ¹⁴C-[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°C. Diesel fuel, motor oil, gasoline, and toluene inhibited ¹⁴C-[lignin]-lignocellulose mineralization by 58, 67, 67, and 86%, respectively. Hexane-treated samples displayed an increase in the rate of ¹⁴C-[lignin]-lignocellulose mineralization of 33%. ¹⁴C-[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.     

Mineralization of Detrital Lignocelluloses by Salt Marsh Sediment Microflora

Specifically radiolabeled ¹⁴C-(cellulose)-lignocellulose and ¹⁴C-(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 CO₂ 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.     

Decomposition of [14C]Lignocelluloses of Spartina alterniflora and a Comparison with Field Experiments

Decomposition of lignocelluloses from Spartina alterniflora in salt-marsh sediments was measured by using ¹⁴C-labeled compounds. Rates of decomposition were fastest in the first 4 days of incubation and declined later. Lignins labeled in side chains were mineralized slightly faster than uniformly labeled lignins; 12% of the [side chain-¹⁴C]lignin-labeled lignocellulose was mineralized after 816 h of incubation, whereas only 8% of the [U-¹⁴C]lignin-labeled lignocelluloses were degraded during this period. The carbohydrate moiety within the lignocellulose complex was degraded about four times faster than the lignin moiety; after 816 h of incubation, 29 to 37% of the carbohydrate moiety had been mineralized. Changes in concentration of lignin and cellulose in litter of S. alterniflora were followed over 2 years of decay. Cellulose disappeared from litter more rapidly than lignin; 50% of the initial content of cellulose was lost after 130 days, whereas lignin required 330 to 380 days for 50% loss. The slow loss of lignin compared with other litter components resulted in a progressive enrichment of litter in lignin content. The rates of mineralization of [¹⁴C]lignocelluloses in marsh sediments were similar to the rates of lignocellulose decomposition in litter on the marsh.     

Influence of Molecular Size and Ligninase Pretreatment on Degradation of Lignins by Xanthomonas sp. Strain 99

The purpose of this study was to examine the relationship between the molecular size of lignin in several preparations and extent of degradation (mineralization) by Xanthomonas sp. strain 99. The influence of ligninase pretreatment was also examined. Five synthetic lignins and one ¹⁴C-methylated spruce lignin were used. The extent of mineralization to ¹⁴CO₂ was greatest for the samples containing the most low-molecular-weight material, and the low-molecular-weight portions were preferentially (or perhaps solely) degraded. Pretreatment of the five synthetic lignins with crude ligninase increased their molecular size and decreased their degradability by the xanthomonad. Pretreatment of the methylated spruce lignin with crude ligninase caused both polymerization and depolymerization but resulted in a net decrease in bacterial degradability. Our results suggest that the xanthomonad can degrade lignins only up to a molecular weight of 600 to 1,000.     

Thermophilic Anaerobic Biodegradation of [14C]Lignin, [14C]Cellulose, and [14C]Lignocellulose Preparations

Thermophilic (55°C) anaerobic enrichment cultures were incubated with [¹⁴C-lignin]lignocellulose, [¹⁴C-polysaccharide]lignocellulose, and kraft [¹⁴C]lignin prepared from slash pine, Pinus elliottii, and ¹⁴C-labeled preparations of synthetic lignin and purified cellulose. Significant but low percentages (2 to 4%) of synthetic and natural pine lignin were recovered as labeled methane and carbon dioxide during 60-day incubations, whereas much greater percentages (13 to 23%) of kraft lignin were recovered as gaseous end products. Percentages of label recovered from lignin-labeled substrates as dissolved degradation products were approximately equal to percentages recovered as gaseous end products. High-pressure liquid chromatographic analyses of CuO oxidation products of sound and degraded pine lignin indicated that no substantial chemical modifications of the remaining lignin polymer, such as demethoxylation and dearomatization, occurred during biodegradation. The polysaccharide components of pine lignocellulose and purified cellulose were relatively rapidly mineralized to methane and carbon dioxide; 31 to 37% of the pine polysaccharides and 56 to 63% of the purified cellulose were recovered as labeled gaseous end products. An additional 10 to 20% of the polysaccharide substrates was recovered as dissolved degradation products. Overall, these results indicate that elevated temperatures can greatly enhance rates of anaerobic degradation of lignin and lignified substrates to methane and low-molecular-weight aromatic compounds.     

Lignin decomposition is sustained under fluctuating redox conditions in humid tropical forest soils

Lignin mineralization represents a critical flux in the terrestrial carbon (C) cycle, yet little is known about mechanisms and environmental factors controlling lignin breakdown in mineral soils. Hypoxia is thought to suppress lignin decomposition, yet potential effects of oxygen (O₂) variability in surface soils have not been explored. Here, we tested the impact of redox fluctuations on lignin breakdown in humid tropical forest soils during ten‐week laboratory incubations. We used synthetic lignins labeled with ¹³C in either of two positions (aromatic methoxyl or propyl side chain C_β) to provide highly sensitive and specific measures of lignin mineralization seldom employed in soils. Four‐day redox fluctuations increased the percent contribution of methoxyl C to soil respiration relative to static aerobic conditions, and cumulative methoxyl‐C mineralization was statistically equivalent under static aerobic and fluctuating redox conditions despite lower soil respiration in the latter treatment. Contributions of the less labile lignin C_β to soil respiration were equivalent in the static aerobic and fluctuating redox treatments during periods of O₂ exposure, and tended to decline during periods of O₂ limitation, resulting in lower cumulative C_β mineralization in the fluctuating treatment relative to the static aerobic treatment. However, cumulative mineralization of both the C_β‐ and methoxyl‐labeled lignins nearly doubled in the fluctuating treatment relative to the static aerobic treatment when total lignin mineralization was normalized to total O₂ exposure. Oxygen fluctuations are thought to be suboptimal for canonical lignin‐degrading microorganisms. However, O₂ fluctuations drove substantial Fe reduction and oxidation, and reactive oxygen species generated during abiotic Fe oxidation might explain the elevated contribution of lignin to C mineralization. Iron redox cycling provides a potential mechanism for lignin depletion in soil organic matter. Couplings between soil moisture, redox fluctuations, and lignin breakdown provide a potential link between climate variability and the biochemical composition of soil organic matter.     

Fungal degradation of kraft lignin and lignin sulfonates prepared form synthetic 14C-lignins

Kraft lignins (KL), bleached kraft lignins (BKL), and lignin sulfonates (LS) were prepared from synthetic ¹⁴C-lignins labeled in the aromatic nuclei or in the propyl side chains. These and control lignins (CL) were incubated with the lignin-decomposing white-rot fungus, Phanerochaete chrysosporium Burds., in a defined culture medium containing cellulose as growth substrate. Decomposition was monitored by measuring the ¹⁴CO₂ evolved. Average percentages of the [ring-¹⁴C]- and [side chain-¹⁴C]-lignins, respectively, recovered as ¹⁴CO₂ at the cessation of ¹⁴CO₂ evolution were: KL, 41 and 31; BKL, 42 and 26; LS, 28 and 21; and CL, 26 and 24. Gel permeation chromatography of radiolabeled materials extracted from spent cultures showed that substantial degradation to nonvolatile products had occurred. The polymeric components in the extracts were further degraded in fresh cultures. These results indicate that industrial lignins are significantly bioalterable, and that under favorable conditions industrial lignins are substantially biodegradable.     

Microbial Decomposition of Wood in Streams: Distribution of Microflora and Factors Affecting [14C]Lignocellulose Mineralization

The distribution and lignocellulolytic activity of the microbial community was determined on a large log of Douglas fir (Pseudotsuga menziesii) in a Pacific Northwest stream. Scanning electron microscopy, plate counts, and degradation of [¹⁴C]lignocelluloses prepared from Douglas fir and incubated with samples of wood taken from the surface and within the log revealed that most of the microbial colonization and lignocellulose-degrading activity occurred on the surface. Labeled lignocellulose and surface wood samples were incubated in vitro with nutrient supplements to determine potential limiting factors of [¹⁴C]lignocellulose degradation. Incubations carried out in a nitrogenless mineral salts and trace elements solution were no more favorable to degradation than those carried out in distilled water alone. Incubations supplemented with either (NH₄)₂SO₄ or organic nitrogen sources showed large increases in the rates of mineralization over incubations with mineral salts and trace elements alone, with the greatest effect being observed from an addition of (NH₄)₂SO₄. Subsequent incubations with (NH₄)₂SO₄, KNO₃, and NH₄NO₃ revealed that KNO₃ was the most favorable for lignin degradation, whereas all three supplements were equally favorable for cellulose degradation. Supplementation with glucose repressed both lignin and cellulose mineralization. The results reported in this study indicate that nitrogen limitation of wood decomposition may exist in streams of the Pacific Northwest. The radiotracer technique was shown to be a sensitive and useful tool for assessing relative patterns of lignocellulose decay and microbial activity in wood, along with the importance of thoroughly characterizing the experimental system before its general acceptance.     

Compositional Characterization and Pyrolysis of Loblolly Pine and Douglas-fir Bark

Two potential biofuel resources, Douglas-fir and Loblolly pine bark, were subjected to extensive chemical and compositional analysis. The barks were initially extracted with dichloromethane, and the resulting extracted compounds were characterized by gas chromatography coupled with mass spectrometric analysis. Characterization of the major bark biocomponents indicated that Douglas-fir and Loblolly pine bark contained 22.5 and 13.2 % tannins, 44.2 and 43.5 % lignin, 16.5 and 23.1 % cellulose, and 7.6 and 14.1 % hemicellulose, respectively. Of particular interest is the high content of tannins and lignin, which make these barks excellent potential precursors for bio-oils and/or other value-added chemicals. ¹³C nuclear magnetic resonance (NMR) was used to characterize the chemical structure of the lignin and tannins. These samples were also analyzed by ³¹P NMR after phosphitylation of the hydroxyl groups in lignin and tannins. The NMR spectral data indicated that the lignin in both barks contained p-hydroxyphenyl (h) and guaiacyl (g) of lignin monomers with an h/g ratio of 10:90 and 22:78 for Douglas-fir and Loblolly pine bark, respectively. Gel permeation chromatography was used to analyze the molecular weight distributions of extracted tannins, isolated cellulose, and ball-milled lignin. The pyrolysis of Douglas-fir and pine bark at 500°C in a tubular reactor generated 48.2 and 45.2 % of total oil, of which the light oil contents are 14.1 and 20.7 % and heavy oil are 34.1 and 24.4 %. Similarly, fast pyrolysis at 375°C yielded 56.1 and 49.8 % of total oil for Douglas-fir and pine bark, respectively.     

Comparative study of lignins isolated from Alfa grass (Stipa tenacissima L.)

Soda lignin, dioxane lignin and milled lignin were isolated from Alfa grass (Stipatenacissima L.). The physico-chemical characterization of three different lignins: one industrial lignin precipitated from soda spent liquor and two lignin preparations isolated under laboratory conditions from Alfa grass (also know as Esparto grass) was performed. The structures of lignins were studied by three non-destructive (FT-IR, solid state ¹³C NMR and UV/visible spectroscopy) and two destructive (nitrobenzene oxidation and thermogravimetric analysis) methods. Elemental analysis and the methoxyl content determination were performed in order to determine the C₉ formulae for the studied lignins. The total antioxidant capacity of the studied lignins has been determined and compared to commercial antioxidants commonly used in thermoplastic industry.     

Litter decay rates are determined by lignin chemistry

Litter decay rates are often correlated with the initial lignin:N or lignin:cellulose content of litter, suggesting that interactions between lignin and more labile compounds are important controls over litter decomposition. The chemical composition of lignin may influence these interactions, if lignin physically or chemically protects labile components from microbial attack. We tested the effect of lignin chemical composition on litter decay in the field during a year-long litterbag study using the model system Arabidopsis thaliana. Three Arabidopsis plant types were used, including one with high amounts of guaiacyl-type lignin, one with high aldehyde- and p-hydroxyphenyl-type lignin, and a wild type control with high syringyl-type lignin. The high aldehyde litter lost significantly more mass than the other plant types, due to greater losses of cellulose, hemicellulose, and N. Aldehyde-rich lignins and p-hydroxyphenyl-type lignins have low levels of cross-linking between lignins and polysaccharides, supporting the hypothesis that chemical protection of labile polysaccharides and N is a mechanism by which lignin controls total litter decay rates. 2D NMR of litters showed that lignin losses were associated with the ratio of guaiacyl-to-p-hydroxyphenyl units in lignin, because these units polymerize to form different amounts of labile- and recalcitrant-linkages within the lignin polymer. Different controls over lignin decay and polysaccharide and N decay may explain why lignin:N and lignin:cellulose ratios can be better predictors of decay rates than lignin content alone.     

Effects of pH on Lignin and Cellulose Degradation by Streptomyces viridosporus

Lignocellulose degradation by Streptomyces viridosporus results in the oxidative depolymerization of lignin and the production of a water-soluble lignin polymer, acid-precipitable polymeric lignin (APPL). The effects of the culture pH on lignin and cellulose metabolism and APPL production by S. viridosporus are reported. Dry, ground, hot-water-extracted corn (Zea mays) lignocellulose was autoclaved in 1-liter reagent bottles (5 g per bottle) and inoculated with 50-ml volumes of S. viridosporus cells suspended in buffers of specific pH (pH 6.0 to 9.2 at 0.4 pH unit intervals). Four replicates of inoculated cultures and of uninoculated controls at each pH were incubated as solid-state fermentations at 37°C. After 6 weeks of incubation the percent loss of lignocellulose, lignin, and carbohydrate and the amount of APPL produced were determined for each replicate. Optimal lignocellulose degradation, as shown by substrate weight loss, was observed in the pH range of 8.4 to 8.8. Only minor differences were seen in the Klason lignin, carbohydrate, protein, and ash contents of the APPLS produced by cultures at each pH. The effects of pH on the degradation of a spruce (Picea pungens) [¹⁴C-lignin]lignocellulose and a Douglas fir (Pseudotsuga menziesii) [¹⁴C-glucan]-lignocellulose were also determined at pH values between 6.5 and 9.5 (0.5 pH unit intervals). The incubations were carried out for 3 weeks at 37°C with bubbler-tube cultures. The percentage of initial ¹⁴C recovered as ¹⁴CO₂, ¹⁴C-labeled water-soluble products, and [¹⁴C]APPL was then determined. The mineralization of lignin and cellulose to CO₂ was optimal at pHs 6.5 and 7.0, respectively. However, the optimum for lignin and cellulose solubilization was pH 8.5, which correlated with the pH 8.5 optimum for APPL production. Overall, the data show that, whereas lignin mineralization is optimal at neutral to slightly acidic pHs, lignocellulose degradation with lignin solubilization and APPL production is promoted by alkaline pHs. These findings indicate that lignin-solubilizing actinomycetes may play an important role in the metabolism of lignin in neutral to alkaline soils in which ligninolytic fungi are not highly competitive.     

The isolation, characterization and effect of lignin isolated from steam pretreated Douglas-fir on the enzymatic hydrolysis of cellulose

Douglas-fir was SO₂-steam pretreated at different severities (190, 200, and 210 °C) to assess the possible negative effect of the residual and isolated lignins on the enzymatic hydrolysis of the steam pretreated substrates. When various isolated lignins were added to the Avicel hydrolysis reactions, the decrease in glucose yields ranged from 15.2% to 29.0% after 72 h. It was apparent that the better hydrolysis yields obtained at higher pretreatment severities were more a result of the greater accessibly of the cellulose rather than any specific change in the non-productive binding of the lignin to the enzymes. FTIR and ¹³C NMR characterization indicated that the lignin in the steam pretreated substrates became more condensed with increasing severity, suggesting that the cellulases were adsorbed to the lignin by hydrophobic interactions. Electrostatic interactions were also involved as the positively charged cellulase components were preferentially adsorbed to the lignins.     

p-Coumaroylation of poplar lignins impacts lignin structure and improves wood saccharification

The enzymatic hydrolysis of cellulose into glucose, referred to as saccharification, is severely hampered by lignins. Here, we analyzed transgenic poplars (Populus tremula × Populus alba) expressing the Brachypodium (Brachypodium distachyon) p-coumaroyl-Coenzyme A monolignol transferase 1 (BdPMT1) gene driven by the Arabidopsis (Arabidopsis thaliana) Cinnamate 4-Hydroxylase (AtC4H) promoter in the wild-type (WT) line and in a line overexpressing the Arabidopsis Ferulate 5-Hydroxylase (AtF5H). BdPMT1 encodes a transferase which catalyzes the acylation of monolignols by p-coumaric acid (pCA). Several BdPMT1-OE/WT and BdPMT1-OE/AtF5H-OE lines were grown in the greenhouse, and BdPMT1 expression in xylem was confirmed by RT-PCR. Analyses of poplar stem cell walls (CWs) and of the corresponding purified dioxan lignins (DLs) revealed that BdPMT1-OE lignins were as p-coumaroylated as lignins from C3 grass straws. For some transformants, pCA levels reached 11 mg·g⁻¹ CW and 66 mg·g⁻¹ DL, exceeding levels in Brachypodium or wheat (Triticum aestivum) samples. This unprecedentedly high lignin p-coumaroylation affected neither poplar growth nor stem lignin content. Interestingly, p-coumaroylation of poplar lignins was not favored in BdPMT1-OE/AtF5H-OE transgenic lines despite their high frequency of syringyl units. However, lignins of all BdPMT1-OE lines were structurally modified, with an increase of terminal unit with free phenolic groups. Relative to controls, this increase argues for a reduced polymerization degree of BdPMT1-OE lignins and makes them more soluble in cold NaOH solution. The p-coumaroylation of poplar samples improved the saccharification yield of alkali-pretreated CW, demonstrating that the genetically driven p-coumaroylation of lignins is a promising strategy to make wood lignins more susceptible to alkaline treatments used during the industrial processing of lignocellulosics.

The expression of a grass p-coumaroyl-CoA:monolignol transferase induces high p-coumaroylation of poplar lignins and better saccharification of alkali-pretreated poplar wood without growth penalty.     

甘肃中东部地区9种薹草属植物分布区群落特征和土壤养分状况

为探究薹草属(Carex L.)植物在不同植被类型中的分布状况,该研究对甘肃中东部地区9种薹草属(Carex L.)植物分布区的群落特征进行调查,并对土壤养分状况进行比较分析,以揭示野生薹草群落物种多样性和分布特征与土壤环境因子间的关系。结果表明：(1) 9种薹草群落物种多样性差异性较大,Shannon-Wiener多样性指数(H)、Simpson优势度指数(D_si)均以青绿薹草群落最高,亚柄薹草最低;Patrick丰富度指数(R)以异穗薹草群落最高,细叶薹草群落最低;Pielou均匀度指数(J_sw)以凹脉薹草群落最高,亚柄薹草最低。(2) 9种野生薹草属植物适宜生长的土壤pH呈中性或弱碱性,且有机质、氮素、钾素含量较丰富,磷含量偏低;土壤有机质、pH、全氮、全磷、全钾、碱解氮、速效磷、速效钾含量的平均值分别为41.07 g·kg^-1、8.35、1.16 g·kg^-1、0.65 g·kg^-1、5.60 g·kg^-1、47.94 mg·kg^-1、5.82 mg·kg^-1和100.60 mg·kg^-1。(3) 9种薹草属植物群落物种多样性与全氮、全磷、全钾、碱解氮、有机质、降雨量和海拔呈正相关关系,而与土壤pH、速效磷、速效钾呈负相关关系,且降雨量、土壤pH、速效磷和有机质对9种野生薹草属植物群落物种多样性影响较大。     

Short communication: Isolation of a bacterium capable of limited degradation of industrial and labelled,natural and synthetic lignins

Pseudomonas putida, isolated from decomposing plant materials, degraded several lignin-related aromatic compounds. After 30 days of incubation in media containing polymeric Kraft-lignin (PKL), the amount of Klason lignin had decreased by about 13%. When ¹⁴C-labelled dehydropolymers of coniferyl alcohol (DHP) lignins and ¹⁴C-lignin-lignocelluloses were used as substrates, mineralization to ¹⁴CO₂ by the P. putida strain ranged from 1.4% to 2.1%.     

Effect of Penicillium chrysogenum on Lignin Transformation

A strain of Penicillium chrysogenum has been isolated from pine forest soils in Tenerife (Canary Islands). This strain was capable of utilizing hydroxylated and nonhydroxylated aromatic compounds, in particular cinnamic acid, as its sole carbon source. In an optimum medium with high levels of nitrogen (25.6 mM) and low levels of glucose (5.5 mM), it was able to decolorize Poly B-411 and to transform kraft, organosolv, and synthetic dehydrogenative polymerisate lignins. After 30 days of incubation, the amount of recovered kraft lignin was reduced to 83.5 and 91.3% of that estimated for uninoculated controls by spectrophotometry and klason lignin, respectively. At the same time, the pattern of molecular mass distribution of the lignin remaining in cultures was changed. The amount of organosolv lignin recovered from cultures was reduced to 90.1 and 94.6% of the initial amount as evaluated by spectrophotometry and klason lignin, respectively. About 6% of total applied radioactivity of O¹⁴CH₃-organosolv lignin was recovered as ¹⁴CO₂ after 30 days of incubation, and 18.5% of radioactivity from insoluble O¹⁴CH₃-organosolv lignin was solubilized. After 26 days of incubation, 2.9% of ¹⁴C-β-dehydrogenative polymerisate and 4.1% of ¹⁴C-ring-dehydrogenative polymerisate evolved as ¹⁴CO₂.     

Direct Compression of Cellulose and Lignin Isolated by a New Catalytic Treatment

Tablet compression of softwood cellulose and lignin prepared by a new catalytic oxidation and acid precipitation method were investigated and compared with the established pharmaceutical direct compression excipients. Catalytic pretreated softwood cellulose (CPSC) and lignin (CPSL) were isolated from pine wood (Pinus sylvestris). The compaction studies were carried out with an instrumented eccentric tablet machine. The plasticity and elasticity of the materials under compression were evaluated using force-displacement treatment and by determining characteristic plasticity (PF) and elasticity (EF) factors. With all biomaterials studied, the PF under compression decreased exponentially as the compression force increased. The compression force applied in tablet compression did not significantly affect the elasticity of CPSC and microcrystalline cellulose (MCC) while the EF values for softwood lignins increased as compression force increased. CPSL was clearly a less plastically deforming and less compactable material than the two celluloses (CPSC and MCC) and hardwood lignin. CPSL presented deformation and compaction behaviour almost identical to that of lactose monohydrate. In conclusion, the direct tablet compression behaviour of native lignins and celluloses can greatly differ from each other depending on the source and isolation method used.     

Biodegradation of 14C-Labeled Model and Cornstalk Lignins, Phenols, Model Phenolase Humic Polymers, and Fungal Melanins as Influenced by a Readily Available Carbon Source and Soil

After 6 months of incubation in a fertile neutral sandy loam, about 48% of the ring carbons and 2-carbons and 60% of the OCH₃ carbons of specifically labeled coniferyl alcohol had evolved as CO₂. After 1 year, corresponding values were 55 and 65%. When coniferyl alcohol units were linked into model and cornstalk lignins, about 23% of the ring carbons and 2-carbons and 39% of the OCH₃ carbons had evolved as CO₂ after 6 months. After 1 year, corresponding values were about 28 and 46%. The addition of orange leaves (0.5%, wt/wt) after 6 months did not significantly increase the evolution of ¹⁴CO₂. Addition of orange leaves (0.5%, wt/wt) with specifically ¹⁴C-labeled pyrocatechol, coumaryl alcohol, model lignins, humic acid-type phenolic polymers and of uniformly ¹⁴C-labeled fungal melanins did not increase labeled C losses or C losses from the orange leaves. Decomposition of protein and pyrocatechol linked into model humic acid polymers, coniferyl alcohol C in model lignins, and Eurotium echinulatum melanin in six soils varied from 2 to 14%. Significant differences in C losses were related to soils and were not influenced by orange leaf applications.     

Treatment of Furfural Residue by Solvent Extraction for Enzymatic Hydrolysis: Effect of Delignification on the Structure and Digestibility

The effect of different treatments on the enzymatic hydrolysis of furfural residue (FR) was investigated in delignification and structural features. In this case, hot water, ethanol, sodium hydroxide, alkali ethanol, and alkaline hydrogen peroxide solution (AHP) were selected as the delignification solvents. The structure and morphology of the original and treated samples were comparatively studied by diffuse reflectance infrared Fourier transform spectrometry (DRIFT), XRD, SEM, and CP/MAS ¹³C NMR. After AHP treatment, the ratio of total lignin to cellulose content in FR and the absorbance ratio of lignin to cellulose (A ₁₅₀₈/A ₁₀₅₇) on the sample surface in the DRIFT spectra was reduced from 0.99 to 0.13 and from 0.40 to 0.04, respectively, which resulted in the highest conversion of cellulose to glucose (99.3 %). It was found that the crystallinity index of FR linearly increased with the decrease of total lignin to cellulose ratio. DRIFT analysis indicated that the high lignin content on the sample surface resulted in a low enzymatic hydrolysis efficiency.