Methane fermentation of xylan by mesophilic and thermophilic methane sludges

The degradation of xylan during methane fermentation proceeded as a first-order reaction. The rate constants were calculated to be 0.40–0.09 day^–1 at 37° C and 0.341 day^–1 at 55° C. From calculations based on the experimental data, K _A and C _A values in the expression of the velocity of xylose consumption changed as the fermentation progressed. In the mesophilic fermentation, the degradation of xylan slowed down after 2 days of incubation, but the rate of consumption of xylose increased between days 3 and 4 of incubation and slow again at the 5th day of incubation. In the thermophilic fermentation, the degradation of xylan proceeded at a constant rate and the rate of consumption of xylose increased slightly on the 3rd day of incubation. When the velocity of gas evolution was determined, the C _G value for acetate at 55° C was about 1.8 times larger than the value at 37° C.     

Oxalic acid, Fe-reduction activity and oxidative enzymes detected in culture extracts recovered from Pinus taeda wood chips biotreated by Ceriporiopsis subvermispora

Pinus taeda wood chips were treated with the biopulping fungus, Ceriporiopsis subvermispora, under solid-state fermentation for periods varying from 7 to 90 days. Low molecular mass compounds and oxidative enzymes were extracted from biotreated wood samples. Manganese-dependent peroxidase was the main oxidative enzyme on all biodegradation periods. Aqueous extracts from biotreated wood presented decreasing pH values, oxalic acid being the major organic acid secreted by the fungus. Analysis of these extracts by gas chromatography coupled with mass spectrometry (GC/MS) revealed small amounts of fatty acids, several short-chain organic acids (C3–C6) and numerous sugar derivatives. 3-methoxy-4-hydroxy benzaldehyde, 3-methoxy-4-hydroxy benzoic acid, 3,4-dihydroxy benzoic acid and tricarboxy-benzene were also found in the wood extracts. A remarkable characteristic of the wood extracts was a strong Fe³⁺-reducing ability. High Fe³⁺-reducing activity and high catechol concentrations were detected in the wood extracts from the undecayed control. This reducing activity and catechol concentrations decreased during the first 7 days of biodegradation. However, from the seventh day of culturing, catechol derivatives coming from lignin degradation start to accumulate in the cultures and Fe³⁺-reduction activity increased again. The Fe³⁺-reduction activity observed in the wood extracts indicates that Fe²⁺ would be available in solution during the wood decay process. Considering that Fe²⁺ and H₂O₂ (produced by this fungus based on MnP-degradation of oxalate) were present in the wood extracts, at least some extent for degradation reactions based on Fenton-chemistry, similarly to the observed in brown-rot fungi, is supposed to occur during wood decay by C. subvermispora.     

Applicability of Coriolopsis rigida for Biodegradation of Polycyclic Aromatic Hydrocarbons

Laccase was produced by Coriolopsis rigida using barley bran as substrate in solid-state fermentation (SSF) and also by submerged fermentation (SmF). The best results were obtained in SSF with twice the amount of laccase production. Laccase could be produced from repeated batch cultures of SSF over 30 days. The laccase degraded several polycyclic aromatic hydrocarbons (PAHs) in vivo and in vitro. The addition of an effective mediator, 1-hydroxybenzotriazol (50 µM), during in vitro treatment increased the degradation rate.     

13C and 1H NMR study of cellulose metabolism by Fibrobacter succinogenes S85

Fibrobacter succinogenes S85, a cellulolytic rumen bacterium, is very efficient in degrading lignocellulosic substrates and could be used to develop a biotechnological process for the treatment of wastes. In this work, the metabolism of cellulose by F. succinogenes S85 was investigated using in vivo 13C NMR and 13C-filtered spin-echo difference 1H NMR spectroscopy. The degradation of unlabelled cellulose synthesised by Acetobacter xylinum was studied indirectly, in the presence of [1-13C]glucose, by estimating the isotopic dilution of the final bacterial fermentation products (glycogen, succinate, acetate). During the pre-incubation period of F. succinogenes cells with cellulose fibres, some cells ('non-adherent') did not attach to the solid material. Results for 'adherent' cells showed that about one fourth of the glucose units entering F. succinogenes metabolism originated from cellulose degradation. A huge reversal of succinate metabolism pathway and production of large amounts of unlabelled acetate which was observed during incubation with glucose only, was found to be much decreased in the presence of solid substrate. The synthesis of glucose 6-phophate was slightly increased in the presence of cellulose. Results clearly showed that 'non-adherent' cells were able to metabolise glucose very efficiently; consequently the metabolic state of these cells was not responsible for their 'non-adherence' to cellulose fibre.     

Influence of tannic acid application on alfalfa hay: in vitro rumen fermentation, serum metabolites and nitrogen balance in sheep

Alfalfa protein is poorly utilised by ruminants due to its rapid degradation in rumen. The objective of the study was to assess the influence of spraying tannic acid (TA) on chopped alfalfa hay on in vitro rumen fermentation and nitrogen (N) retention by sheep. Alfalfa hay with and without TA was fed to sheep to determine nutrient digestibility and N balance. TA was sprayed on chopped alfalfa at three concentrations to determine its effect on in vitro fermentation of dry matter (DM) and N balance in sheep. Final TA concentrations were 0, 30, 60 and 90 g TA per kg DM. The control was sprayed with the same amount of water but without TA. In vitro DM degradation and the production of gas, ammonium-N (NH4-N) and short-chain fatty acid (SCFA) were measured. TA-sprayed alfalfa and the control were fed to sheep to determine nutrient digestibility and N retention. Addition of TA had no influence on the extent and rate of gas production but significantly decreased NH4-N concentration at 30 (P < 0.05), 60 and 90 (P < 0.0001) g/kg DM. Addition of polyethylene glycol (PEG) to TA-sprayed alfalfa increased NH4-N to a level comparable to non-TA-sprayed alfalfa. Spraying of alfalfa with TA significantly decreased (P < 0.05) isovalerate but did not affect the total and individual SCFA acid production. Tannic acid significantly (P < 0.05) reduced in vitro true degradability of DM (IVTD) after 24 h incubation at levels of 60 and 90 g TA per kg DM. Neutral-detergent fibre digestibility (dNDF) after 24 h (P < 0.01), 60 and 90 (P < 0.0001) g TA per kg DM. The effect of TA on either IVTD or dNDF was not significant (P > 0.05) after 48 h of incubation. There was a strong linear relationship between percentage increase in gas production due to PEG and protein precipitation capacity (R2 = 0.94). N digestibility was significantly reduced with all three levels of TA additions. However, the proportion of urine-N to total N output was reduced by adding 60 g (P < 0.05) and 90 g (P < 0.01) TA per kg DM. Serum metabolites and liver enzymes were not affected by TA (P > 0.05). Higher faecal N as the TA level increased indicates incomplete dissociation of tannin-protein complexes post ruminally. Factors affecting dissociation of tannin-protein complexes need further study.     

Substrate-dependent degradation patterns in the decay of wheat straw and beech wood by ligninolytic fungi

Summary The ability of 45 fungal strains to degrade wheat straw and beech wood was studied. Degradation patterns were defined in terms of chemical evolution of substrates and changes in lignin and polysaccharides. Trametes versicolor produced an important degradation of lignin and increased substrate digestibility, but it caused high weight losses and gave rise to similar decay patterns on both substrates. A preferential degradation of lignin was produced during straw transformation by Pleurotus eryngii. The increase of soluble lignin and decreases of lignin content and H/C ratio defined the degradation tendency after principal component analysis. The cation exchange capacity and water and alkali solubility presented the highest loading factors for the characterization of fungal transformation of beech wood. Offprint requests to: A. T. Martínez     

EFFECTS OF LONG-TERM SUBMERGENCE ON SURVIVAL AND RECOVERY GROWTH OF FOUR RIPARIAN PLANT SPECIES IN THREE GORGES RESERVOIR REGION, CHINA

 地瓜藤(Ficus tikoua)、荻(Triarrhena sacchariflora)、牛鞭草(Hemarthria altissima)和狗牙根(Cynodon dactylon)是三峡库区常见的岸生植物, 自然分布于河岸带不同垂直高程的地段。为了明确它们在成库后“三峡库区消落区”长期完全水淹条件下的存活和生长情况, 实验设置对照(不进行水淹, 常规供水管理)和完全水淹两个处理, 30、60、90、120、150和180 d 6个水淹时间水平, 研究了4种植物在完全水淹条件下的存活、生物量变化和恢复生长。结果发现: 1) 4种植物在完全水淹条件下的存活率与其在河岸带上的垂直分布高程密切相关。分布于距江面高程较高的河岸段的地瓜藤植株, 在全淹30 d后就全部死亡; 分布在中高程河岸段的荻在全淹150和180 d后全部死亡; 可以分布于低高程河岸段的牛鞭草和狗牙根, 淹没180 d后存活率分别为90%和100%。2)全淹抑制了荻、牛鞭草和狗牙根的生长, 总生物量增量显著低于对照植株。与水淹0 d相比, 全淹处理植株的地上部分生物量显著降低, 荻在全淹60和120 d后, 地下部分生物量显著降低, 但牛鞭草和狗牙根的地下部分生物量与水淹0 d水平相比无显著差异。3)水淹处理结束后, 存活的荻、牛鞭草和狗牙根植株都能很好地恢复生长。在恢复生长过程中, 全淹30、60和90 d后, 荻、牛鞭草和狗牙根植株的总分枝长相对生长速率与对照植株无显著差异, 全淹120、150和180 d后, 牛鞭草和狗牙根植株的总分枝长相对生长速率显著高于对照植株。全淹处理的荻、牛鞭草和狗牙根植株的总叶片数相对生长速率始终显著高于对照植株。遭受长期完全水淹后, 植株在有限的营养储备条件下, 快速产生叶片以迅速积聚光合产物可能是植物更为优化的恢复生长方式。     

Effects of monolaurin on ruminal methanogens and selected bacterial species from cattle, as determined with the rumen simulation technique

Before being able to implement effective ruminal methane mitigation strategies via feed supplementation, the assessment of side effects on ruminal fermentation and rumen microbial populations is indispensable. In this respect we investigated the effects of monolaurin, a methane-mitigating lipid, on methanogens and important carbohydrate-degrading bacteria present in ruminal fluid of dairy cattle in continuous culture employing the rumen simulation technique. In six experimental runs, each lasting for 10 days, four diets with different carbohydrate composition, based on hay, maize, wheat and a maize-wheat mixture, either remained non-supplemented or were supplemented with monolaurin and incubated in a ruminal-fluid buffer mixture. Incubation liquid samples from days 6 to 10 of incubation were analyzed with relative quantitative polymerase chain reaction (qPCR) of 16S rRNA genes to assess monolaurin-induced shifts in specific rumen microbial populations in relation to the corresponding non-supplemented diets. Monolaurin completely inhibited Fibrobacter succinogenes in all diets while the response of the other cellulolytic bacteria varied in dependence of the diet. Megasphaera elsdenii remained unaffected by monolaurin in the two diets containing maize, but was slightly stimulated by monolaurin with the wheat and largely with the hay diet. The supply of monolaurin suppressed Methanomicrobiales below the detection limit with all diets, whereas relative 16S rRNA gene copy numbers of Methanobacteriales increased by 7-fold with monolaurin in case of the hay diet. Total Archaea were decreased by up to over 90%, but this was significant only for the wheat containing diets. Thus, monolaurin exerted variable effects mediated by unknown mechanisms on important ruminal microbes involved in carbohydrate degradation, along with its suppression of methane formation. The applicability of monolaurin for methane mitigation in ruminants thus depends on the extent to which adverse effects on carbohydrate-degrading bacteria actually impair the supply of digested carbohydrates to the animal.     

Lignin biodegradation and ligninolytic enzyme studies during biopulping of Acacia mangium wood chips by tropical white rot fungi

White rot fungi are good lignin degraders and have the potential to be used in industry. In the present work, Phellinus sp., Daedalea sp., Trametes versicolor and Pycnoporus coccineus were selected due to their relatively high ligninolytic enzyme activity, and grown on Acacia mangium wood chips under solid state fermentation. Results obtained showed that manganese peroxidase produced is far more compared to lignin peroxidase, suggesting that MnP might be the predominating enzymes causing lignin degradation in Acacia mangium wood chips. Cellulase enzyme assays showed that no significant cellulase activity was detected in the enzyme preparation of T. versicolor and Phellinus sp. This low cellulolytic activity further suggests that these two white rot strains are of more interest in lignin degradation. The results on lignin losses showed 20–30% of lignin breakdown at 60 days of biodegradation. The highest lignin loss was found in Acacia mangium biotreated with T. versicolor after 60 days and recorded 26.9%, corresponding to the percentage of their wood weight loss recorded followed by P. coccineus. In general, lignin degradation was only significant from 20 days onwards. The overall percentage of lignin weight loss was within the range of 1.02–26.90% over the biodegradation periods. Microscopic observations conducted using scanning electron microscope showed that T. versicolor, P. coccineus, Daedalea sp. and Phellinus sp. had caused lignin degradation in Acacia mangium wood chips.     

Chitosanases in the autolysis of Mucor rouxii

The mycelium of Mucor rouxii reached a 50% degree of lysis after 50 days incubation, and was then stable with the incubation time. The pH of the medium was 4.3 when autolysis began, rising to pH 7.6 after 6 days of autolysis and remaining there for the duration of the experiment. Maximum degradation of mycelium occurs during the first days of autolysis. Glucosamine is present in the culture liquid during all the autolytic process. Enzymes implicated in the degradation of chitosan and chitin were studied in the culture fluid during autolysis. An exochitosanase activity was detected after a day of autolysis, and its activity increased during 20 days of autolysis and afterwards remained constant until the end of the process. An endochitosanase activity was detected in the culture fluid from the beginning of the autolysis, having its maximum activity after 34 days of incubation. Both activities show an optimum pH of 5.5, but the pH range of activity for endochitosanase was broader than for exochitosanase. Both activities were not inhibited by 0.5 mM glucosamine. Activities of the enzymes B-N-acetylglucosaminidase and chitinase were not found. The chitosan content in the cell walls decreased with the incubation time. In these cell walls the chitin content experienced an increase at the beginning of the autolysis, decreasing afterwards. The enzymatic complex obtained from autolyzed cultures of M. rouxii hydrolyzed 2-day-old cell walls of this fungus. The hydrolysis was 21% after 24 h of incubation, liberating glucose and glucosamine. As a consequence protoplasts from M. rouxii germinated spores were obtained with its own lytic enzymes in adequate osmotic conditions. The involvement of chitosanases in the autolysis of this fungus have been studied.     

Cultivation of Lentinus subnudus Berk (Polyporales: Polyporaceae) on woodlogs

Studies were carried out on the cultivability of Lentinus subnudus on woodlogs of various hardwood trees and the effect of chemical treatments of these woodlogs with citric, tartaric, indole-3-acetic (IAA) and gibberellic (GA3) acids on fruitbody production and yield. Of the four hardwood species of Chlorophora excelsa, Terminalia ivorensis, Terminalia superba and Spondias mombin tried, woodlogs of C. excelsa were the best in supporting L. subnudus fructification, followed by those of S. mombin. On the effect of chemical treatments of C. excelsa and S. mombin woodlogs on L. subnudus' fruitbody production and yield, bed logs treated with 50 ppm indole-3-acetic and gibberellic acids were the best in enhancing fructification and yield with C. excelsa GA3 and IAA treated bed logs consistently producing more fruitbodies and greater yields than S. mombin bed logs given the same treatments. The implication of these findings in relation to results obtained in previous studies are discussed.     

Growth of Arthrobotrys superba from a birch wood resource base into soil determined by radioactive tracing

The ability of a nematode-trapping fungus to establish in field soil is an important characteristic when considering its use as a biological control agent. The outgrowth of the nematode-trapping fungus Arthrobotrys superba from wood was recorded by labelling the fungus with [(14)C]3-O-methylglucose and [(32)P]orthophosphoric acid and by using the soil sprinkling method. The fungus reached a distance of 7-8 cm during 25 days in heat-treated (60 degrees C) soil, detected by either radioactive tracing or the soil sprinkling technique. The two labelled compounds were co-distributed at all sampling times (r(2)=0.946) which indicates that the glucose pool (as methylglucose) and phosphorus content were correlated throughout the mycelium. In natural, non-heat-treated soil the fungus reached a distance of 1.5 cm from one disc of birch wood after 30 days, while it reached 3.2 cm during the same period when the food base was a pile of five inoculated discs. The experiments showed, for the first time, that a nematophagous fungus, A. superba, can grow out into soil from a piece of wood and supported by nutrients translocated from the resource base to the edge of the mycelium.     

EFFECTS OF MORINGA OLEIFERA SEED EXTRACT ON RUMEN FERMENTATION IN VITRO

Moringa oleifera is a pantropical tree of the family Moringaceae. A previously undescribed property of an aqueous extract from the seeds of this plant is the modulation of ruminal fermentation patterns, especially protein degradation, as demonstrated in a short-term batch incubation system. Gas, short chain fatty acids (SCFA) and cellulolytic enzyme activities were determined as general fermentation parameters. A dot blot assay able to directly detect true protein in rumen fluid samples was used to quantify protein degradation. For complex substrates the interpretation of protein degradation profiles was amended by polyacrylamide gel electrophoresis (PAGE) of the samples. When incubated with pure carbohydrates at a concentration of 1 mg ml^–1, the extract reduced microbial degradation of the model protein, bovine serum albumin (BSA), such that its concentration was at least 40% above the control after 12 h of incubation. Total protein degradation was thus delayed by approximately 9 h. When fermented along with wheat straw, leaf protein (Rubisco) was almost entirely protected during 12 h of fermentation. The degradation of soy proteins was retarded by at least 4- 6 h, depending on the protein band. There were strong side effects on the fermentation of pure cellulose (SCFA yield -60% after 12 h), whereas cellobiose and starch fermentation were less affected (-18 and -8%, respectively). When the complex substrates were fermented, SCFA yield was reduced by approximately 30% after 12 h. In our work we clearly demonstrate the efficacy of the new substance, which is neither a tannin nor a saponin, in an in vitro system, using pure as well as complex substrates. The properties shown in vitro for the crude extract suggest that it could have a positive effect on the protein metabolism of ruminants under intensive management and that negative side effects can be overcome by an optimized dosage. If the chemical nature of the active substance and its mechanism of action can be clarified, it may provide an alternative to replace critical synthetic feed additives (such as antibiotics) for high yielding dairy cows.     

Effect of fumarate reducing bacteria on in vitro rumen fermentation,methane mitigation and microbial diversity

The metabolic pathways involved in hydrogen (H₂) production, utilization and the activity of methanogens are the important factors that should be considered in controlling methane (CH₄) emissions by ruminants. H₂ as one of the major substrate for CH₄ production is therefore should be controlled. One of the strategies on reducing CH₄ is through the use of hydrogenotrophic microorganisms such as fumarate reducing bacteria. This study determined the effect of fumarate reducing bacteria, Mitsuokella jalaludinii, supplementation on in vitro rumen fermentation, CH4 production, diversity and quantity. M. jalaludinii significantly reduced CH₄ at 48 and 72 h of incubation and significantly increased succinate at 24 h. Although not significantly different, propionate was found to be highest in treatment containing M. jalaludinii at 12 and 48 h of incubation. These results suggest that supplementation of fumarate reducing bacteria to ruminal fermentation reduces CH₄ production and quantity, increases succinate and changes the rumen microbial diversity.     

Activation of fermentation by salts in Debaryomyces hansenii

The presence of 1.0 M KCl or NaCl during growth of Debaryomyces hansenii results in increased ethanol production. An additional increase of fermentation was observed when the salts were also present during incubation under nongrowing conditions. Extracts of cells grown in the presence of salt showed increased alcohol dehydrogenase and phosphofructokinase activities, indicating that these enzymes are responsible for the increased fermentation capacity. This is confirmed by measurements of the glycolytic intermediates. The increased fermentation capacity of the cells grown with salts seems to enable them to cope with the additional energy required for uptake and/or efflux of cations.     

Effect of Manganese on Lignin Degradation by Pleurotus ostreatus during Solid-State Fermentation

Lignin degradation by Pleurotus ostreatus was studied under solid-state fermentation (SSF) in chemically defined medium containing various levels of Mn. Degradation of [¹⁴C]lignin prepared from cotton branches to soluble products, as well as its mineralization to ¹⁴CO₂, was enhanced by the addition of Mn. The effect of malonate on lignin mineralization was most marked during the first 10 days of SSF, in a treatment amended with 73 μM Mn. A high concentration of Mn (4.5 mM) caused inhibition of both fungal growth and mineralization rates during the first 2 weeks of incubation. Addition of malonate reversed this effect because of chelation of Mn. Mn was found to precipitate in all treatments, with or without the addition of malonate. α-Keto-γ-methiolbutyric acid cleavage to ethylene, an indication of ^. OH production, was observed as early as 3 days of incubation in all treatments.     

Effects of Incubation Time and Temperature on In Vitro Selective Delignification of Silver Leaf Oak by Ganoderma colossum

The effects of incubation time and temperature on the ability of isolates of the chlamydosporic and thermophilic fungus Ganoderma colossum (Fr.) C. F. Baker to cause selective delignification of Quercus hypoleucoides A. Camus were evaluated by standard in vitro agar block tests. Chemical and scanning electron microscopy studies of decayed wood were used to determine the extent of selective delignification or simultaneous decay caused by each fungal isolate. At 35 deg C, the percent weight loss increased from 6.1% after 4 weeks to a maximum of 32.5 to 33.0% after 16 and 20 weeks of incubation. The average percent Klason lignin-chlorite holocellulose ratios (PKL/CHC) decreased from 0.35 in the control wood block to 0.22 in wood blocks incubated for 12 weeks; this indicated selective delignification. The average PKL/CHC increased for the 16- and 20-week incubation periods, indicating greater removal of polysaccharides during longer incubation periods. In temperature studies, the percent weight loss after 12 weeks was 26 to 27% between 30 and 40 deg C and less than 16% for the 25 and 45 deg C treatments. The average PKL/CHC ranged from 0.18 to 0.16 between 35 and 40 deg C, whereas they were 0.23 and 0.31 for the 25 and 45 deg C treatments, respectively. Scanning electron microscopy confirmed an optimum temperature range near 35 to 40 deg C and incubation times of 8 to 12 weeks for selective delignification. Under these conditions, ray parenchyma, fiber tracheids, and vessels were devoid of middle lamella; pit regions of cells were visible with significantly enlarged apertures; and individual cells were separated and clearly delimited. Extensive delignification of wood occurred throughout the wood blocks evaluated. Incubation times longer than 12 weeks resulted in greater degradation of wood cell walls and thus in greater removal of the polysaccharide component of the wood. For incubation times of 4 weeks or a temperature of 25 deg C, limited to no degradation of cells was observed. At 45 deg C, walls of fiber tracheids were eroded and ray parenchymal cells were extensively degraded, indicating that simultaneous degradation of cell walls occurred. Thus, the incubation temperature influenced the type of decay by G. colossum observed on oak wood blocks: extensive selective delignification at 35 to 40 deg C after more than 8 weeks of incubation or simultaneous decay at 45 deg C with 14% weight loss after 12 weeks of incubation. Isolates of G. colossum may prove useful in studies on mechanisms of delignification and biotechnological applications (e.g., biopulping) of lignin-degrading fungi.     

Biodegradation of wheat straw lignocarbohydrate complexes (LCC)

Summary In laboratory and semi-industrial scale experiments the influence of the substrate water content, temperature, and incubation time on the progress of solid state fermentation of straw colonized by white rot fungi was investigated. The parameters used to evaluate the fermentation process were degradation of total organic matter and lignin, in vitro digestibility, the content of water soluble substances in the substrate and the pH.The degradation of total organic matter was species specific. Only Trametes hirsuta enhanced the degradation at elevated temperature (30 °C). With Abortiporus biennis, Ganoderma applanatum, and Pleurotus serotinus, elevated temperature had and adverse effect. Prolonged incubation only improved degradation of straw by the relatively slowgrowing fungi Ganoderma applanatum, Lenzites betulina, and Pleurotus sajor caju.Elevated temperature and prolonged incubation shifted the relative degradation rates in favour of total organic matter degradation. With Ganoderma applanatum, Pleurotus ostreatus, and Pleurotus serotinus lignin degradation, even on an absolute scale, was less at 30 °C than at 22 °C.In general, the in vitro digestibility also decreased, when the incubation time and temperature were raised. With Ganoderma applanatum the in vitro digestibility dropped below the value of the sterile straw control.Solid state fermentation of straw was at an optimum at a medium water content of 75 ml/25 g of substrate. However, most of the fungi tested could digest straw over a wide range of water content. At higher water contents (125–150 ml/25 g of substrate) an increased production of aerial mycelium was observed.In semi-industrial batch experiments (40 kg) with Abortiporus biennis the in vitro digestibility dropped below the reference value for sterile straw during the first 19 days of incubation. Later, the in vitro digestibility again rose and reached its optimum after about 60 days. The in vitro digestibility in the semi-industrial experiments was always lower than in the laboratory experiments (+9% and +25%, respectively).In long term experiments (2.5 kg batches, 8 months of incubation) very different values for the in vitro digestibility were found, and these depended on the fungus used (Abortiporus biennis, +16%; Pleurotus ostreatus, +4%; and Ganoderma applanatum, –27%).     

Biological Delignification of Aspen Wood by Solid-State Fermentation with the White-Rot Fungus Merulius tremellosus

Solid-state fermentation of aspen (Populus tremuloides) wood with Merulius tremellosus for 8 weeks removed 52% of the lignin but only 12% of the total wood weight, and increased the cellulase digestibility to 53% from 18%. Water-soluble and enzyme-solubilized lignin degradation products accumulated. Delignification was fastest at temperatures between 25 and 32.5°C and at a water-to-wood ratio of 2. Initial pH values between 4 and 6 were optimal; M. tremellosus acidified the wood to below pH 3.5 as it grew. The fungus tolerated CO₂ concentrations of at least 14% and O₂ concentrations down to 7% in the bulk gas phase. Both simple and complex nitrogen supplements inhibited delignification. Supplementary KH₂PO₄, MgSO₄, CaCl₂, thiamine, and trace elements had little effect on the fermentation. Four isolates of M. tremellosus had very similar abilities to delignify aspen wood. Biological delignification with M. tremellosus may be a useful pretreatment for enzymatic saccharification or ruminant feeding.     

Improvement of dry matter digestibility of water hyacinth by solid state fermentation using white rot fungi

Feeding value of water hyacinth biomass colonized by three species of white rot fungi during solid-state fermentation was investigated. All three organisms proved to be efficient degraders and enhanced dry matter digestibility. Loss of organic matter was maximum (23.6+/-0.1% dry wt) after 48 days by P. ostreatus. C. indica showed maximum cellulose degradation (18.5+/-0.1% dry wt) than other two fungi after 48 days of incubation. In all cases, an extensive removal of hemicellulose at the initial growth period and a delayed degradation of lignin were observed. Hemicellulolysis was maximum (46.3+/-0.1% dry wt) by C. indica, but delignification (14.2+/-0.2% dry wt) by P. sajor-caju after 48 days. The amount of reducing sugar in the degraded biomass decreased at early stages, but increased as degradation progressed in all three cases (maximum 1.1+/-0.05% dry wt after 48 days by C. indica). Soluble nitrogen content increased only during 16-32 days of incubation (highest 1.1+/-0.1% dry wt after 32 days by P. sajor-caju). Crude protein of the bioconverted biomass increased gradually up to 32 days but decreased thereafter (maximum 10.3+/-0.1% dry wt after 32 days by P. sajor - caju). Per cent change in in vitro dry matter digestibility of degraded substrates enhanced gradually after 8 days and reached maximum after 32 days but thereafter decreased (highest + 20.4+/-0.3% dry wt by P. sajor-caju). The results demonstrated the efficient degrading capacity of the test fungi and their potential use in conversion of water hyacinth biomass into mycoprotein-rich ruminant feed, more so by P. sajor-caju.