Influence of nutritional supplementation on solid-substrate fermentation of wheat straw with an alkaliphilic white-rot fungus (Coprinus sp.)

Summary The solid-substrate fermentation of wheat straw with an alkaliphilic white-rot fungus (Coprinus sp.) was found to be influenced by the levels of nitrogen, phosphorus+sulphur and free carbohydrates, in terms of biodegradation of straw ingredients, microbial protein production and changes in in-vitro dry matter digestibility (IVDMD). Nitrogen and Phosphorus+Sulphur compounds favoured the bioconversion and their optimum levels were (g/100 g DM): urea (sterile): 1.5, urea (unsterile): 3.0; superphosphate: 1.0. The addition of free carbohydrates as molasses and whey had detrimental effect on biodegradation of lignin as also on organic matter degradation and digestibility. However, the protein production was enhanced in the supplemented straw. The optimized laboratory fermentation was also extended to 4 kg-(sterile and unsterile) and 50 kg-(unsterile) fermentation.     

Effect of different supplements on bioprocessing of wheat straw by Phlebia brevispora: changes in its chemical composition, in vitro digestibility and nutritional properties

Bioprocessing of wheat straw was carried out by Phlebia brevispora under solid state conditions. Effect of different supplements on lignocellulolytic enzymes production, degradation of straw cell wall fibers and its resultant effect on nutritional quality of wheat straw were studied. Ammonium chloride and malt extract were more effective in terms of ligninolysis and enhanced in vitro digestibility. The concentration of the selected supplements and the moisture content was worked out using response surface methodology in order to minimize the loss in total organic matter so as to selectively degrade lignin. The experiment was scaled up to batches of 200 g under optimized conditions and the degraded substrate was analyzed for its biochemical properties. P. brevispora degraded 290 g/kg of lignin and enhanced the in vitro digestibility from 150 to 268 g/kg (78%). Crude protein, amino acids, total phenolic contents and antioxidant properties were significantly higher in degraded straw.     

Solid state fermentation of oat straw by Polyporus sp A-336 and the effect of added sugars

Summary Supplementing oat straw in SSF by Polyporus sp A-336 with xylose, mannose, glucose and arabinogalactan at levels of 5 and 10% of straw weight stimulated lignin degradation and cellulose hydrolysis. Degradation of lignin, hemicellulose and cellulose was monitored for 30 days in plain straw, and straw plus xylose and showed that xylose shortened the lag in lignin breakdown and slowed hemicellulose utilization. At 24 days, similar polymer losses occurred in both systems and enzymatic cellulose hydrolysis had reached a maximum of 47% weight loss.     

Solid state fermentation of lignocellulose containing plant residues withSporotrichum pulverulentum Nov. andDichomitus squalens (Karst.) Reid.

Summary The fermentation profiles ofSporotrichum pulverulentum andDichomitus squalens showed distinct differences.D. squalens digested the substrate more slowly thanSporotrichum pulverulentum. The relative degradation rates of total organic matter and lignin also differed considerably.Whereas withS. pulverulentum the ratio was about the same throughout the whole observation period, withDichomitus squalens it altered in favour of lignin degradation.WithSporotrichum pulverulentum an optimum digestion in vitro of 40%–50% was achieved after 20 days of incubation. WithDichomitus squalens the best value (about 60%) was reached after 30 days of incubation. Increasing incubation temperatures enhanced the degradation of the substrate.As found with wheat straw, all other substrates tested (straw of rape and barley, glumes of rice) were degraded more slowly byDichomitus squalens than bySporotrichum pulverulentum. The degradation rates for oak, spruce and beech sawdust were very low compared to those for straw.Small amounts of ammonium nitrate stimulated the degradation of straw byS. pulverulentum whereas higher concentrations had an inhibitory effect. The optimum water content of the substrate, measured by decomposition of total organic matter and lignin and by in vitro digestibility, was between 50 and 100 ml of water/25 g substrate. Higher and lower water contents had an unfavourable effect.Varying the pore size of the substrate by using milled straw of defined particle size had no influence on the 6 parameters tested under the given experimental conditions.The best method to supress potential competitors was to heat the substrate to 90°C for 24 h.     

The effect of white-rot basidiomycetes on chemical composition andin Vitro digestibility of wheat straw

Five white-rot basidiomycetes were evaluated for their potential to improve ruminal degradation of wheat straw.Polyorus brumalis, Lyophyllum ulmarium III,Trametes gibbosa, Pleurotus ostreatus, and aPleurotus ostreatus mutant were incubated on wheat straw for 30 d at 28°C. Detergent fiber, crude protein andin vitro dry matter digestibility (IVDMD) were determined. The results showed increasing crude protein and ash contents in fungus-treated straw. IVDMD values were increased in straws treated withP. ostreatus, P. ostreatus mutant andT. gibbosa only. Relative to untreated wheat straw the detergent fiber content—neutral detergent fiber (NDF), and acid detergent fiber (ADF) was reduced in fungus-treated straw and out of three fractions—hemicellulose, cellulose and lignin, hemicellulose showed the largest proportionate loss whereas lignin the smallest one in all 5 samples of fungus treated straw.     

White-rot fungal conversion of wheat straw to energy rich cattle feed

In order to improve the digestibility and nutrient availability in rumen, wheat straw was subjected to solid state fermentation (SSF) with white-rot fungi (i.e. Pleurotus ostreatus and Trametes versicolor) and the fermented biomass (called myco-straw) was evaluated for biochemical, enzymatic and nutritional parameters. The fungal treatment after 30 days led to significant decrease (P < 0.05) in cell wall constituents viz, acid detergent fiber (ADF), neutral detergent fiber (NDF), hemicellulose, lignin and cellulose to the extent of 35.00, 38.88, 45.00, 37.48 and 37.86%, respectively in P. ostreatus fermented straw, while 30.04, 33.85, 39.90, 31.29 and 34.00%, respectively in T. versicolor fermented straw. However, maximum efficiency of fermentation in terms of low carbohydrate consumption per unit of lignin degradation, favoring cattle feed production was observed for P. ostreatus on the 10th day (17.12%) as compared with T. versicolor on the 30th day (16.91%). The myco-straw was found to contain significantly high (P < 0.05) crude protein (CP; 4.77% T. versicolor, 5.08% P. ostreatus) as compared to control straw (3.37%). Metabolizable energy (ME, MJ/kg DM), percent organic matter digestibility (OMD) and short chain fatty acids (SCFAs; mmol) production also increased considerably from control straw (4.40, 29.91 and 0.292) to a maximum up to P. ostreatus fermented straw (4.92, 33.39 and 0.376 on 20th day) and T. versicolor fermented straw (4.66, 31.74 and 0.334 on 10th day), respectively. Moreover, the myco-straw had lower organic carbon and was rich in nitrogen with lower C/N ratio as compared to control wheat straw. Results suggest that the fungal fermentation of wheat straw effectively improved CP content, OM digestibility, SCFAs production, ME value and simultaneously lowered the C/N ratio, thus showing potential for bioconversion of lignin rich wheat straw into high energy cattle feed.     

Effects of air pressure oscillation amplitude on oxygen transfer rate and biomass productivity in a solid-state fermenter

The modified sulfite oxidation method was adapted for estimation of the overall oxygen transfer rate in a pressure oscillating, solid-state fermenter. At 4.5 atm and 30 °C, the oxygen transfer rate reached 717 mmol kg^–1 initial dry matter h^–1 in this system against 37 mmol kg^–1 initial dry matter h^–1 in a static tray fermenter. At 30 °C and 3 atm, Azotobacter vinelandii grew on wheat straw and reached 4.7×10¹⁰ c.f.u. g^–1 substrate dry matter after 36 h, while only 8.2×10⁹ c.f.u. g^–1 substrate dry matter was obtained in a static tray system.     

Effect of six species of white-rot basidiomycetes on the chemical composition and rumen degradability of wheat straw

This study was conducted to investigate changes in in vitro dry matter digestibility (IVDMD), volatile fatty acids (VFA) production and cell-wall constituent degradation in wheat straw treated with six white-rot fungi: Daedalea quercina, Hericium clathroides, Phelinus laevigatus, Inonotus andersonii, Inonotus obliquus, and Inonotus dryophilus. The incubation of wheat straw for 30 days at 28 C improved IVDMD from 41.4 (control) to 59.2% for D. quercina, 56.3% for H. clathroides, 50.2% for P. laevigatus, 51.4% for I. andersonii, 52% for I. obliquus, and 55.9% for I. dryophilus. In contrast, the growth of fungi was accompanied by the dry matter loss of wheat straw: 43% for D. quercina, 12% for H. clathroides, and 22-25% for the other fungi. It is evident that the increase in digestibility by D. quercina was not offset by a loss of dry matter. The total VFA production during the rumen fermentation of fungus-treated straw was slightly increased by H. clathroides and I. dryophilus only. Neutral detergent fiber (NDF) and acid detergent fiber (ADF) were reduced in fungus-treated straw. Out of the three fractions (hemicellulose, cellulose, and lignin), hemicellulose and lignin showed the largest proportionate loss after inoculation with the fungi D. quercina, H. clathroides, P. laevigatus, and I. obliquus. The other two fungi showed the largest proportionate loss in cellulose and hemicellulose contents. The results of this study suggest that the digestion enhancement of wheat straw colonized by white-rot fungi is regulated by complex factors including the degradation of structural carbohydrates and lignin.     

Solid state fermentation and fractionation of oat straw by Basidiomycetes

Summary Seventee white-rot and brown-rot fungi were screened for their ability to fractionate the lignocellulose structure of oat straw through the preferential attack of lignin or cellulose. Fermentations were carried out under solid-state conditions with 25 g quantities of straw. The fermented straw was analyzed for weight loss, Klason lignin loss and cellulase digestion. All the fungi attacked both lignin and carbohydrate fractions causing 3–28% weight losses and 26–34 g/100 g enzymatic digestibility. Polyporus tulipiferae, Phanerochaete chrysosporium and Polyporus sp. were tested for the effects of various nitrogen, phosphate and carbon levels, incubation temperatures and incubation time. The three fungi had different responses to these factors.     

Biodelignification of wheat straw and its effect on in vitro digestibility and antioxidant properties

A variety of methods for feed development have been introduced during last few years. Bioprocessed agricultural residues may prove a better alternative to provide animal feed. For the purpose, some white rot fungi were allowed to degrade wheat straw up to 30 days under solid state conditions. Several parameters including loss in total organic matter, ligninolysis, in vitro digestibility of wheat straw and estimation of different antioxidant activities were studied. All the fungi were able to degrade lignin and enhance the in vitro digestibility. Among all the tested fungi, Phlebia brevispora degraded maximum lignin (30.6%) and enhanced the digestibility from 172 to 287 g/kg. Different antioxidant properties of fungal degraded wheat straw were higher as compared to the uninoculated control straw. Phlebia floridensis found to be more efficient organism in terms of higher antioxidant activity (70.8%) and total phenolic content (9.8 mg/ml). Thus, bioprocessing of the wheat straw with the help of these organisms seems to be a better approach for providing the animal feed in terms of enhanced digestibility, higher protein content, higher antioxidant activity and availability of biomass.     

Degradation of Lignin by Cyathus Species

The ability of 12 Cyathus species to degrade ¹⁴C-labeled lignin in kenaf was studied. The sum of ¹⁴C released into solution plus ¹⁴C released into the gas phase over a 32-day fermentation period was used to determine average daily rates of lignin biodegradation. Cyathus pallidus. C. africanus, and C. berkeleyanus delignified kenaf most rapidly. C. canna showed the greatest preference for lignin degradation over other plant components, and its rate of lignin degradation was only slightly lower than the three most active species. The apparent ability of fungi to metabolize low-molecular-weight lignin breakdown products correlated well with their overall delignification rates. C. stercoreus metabolized degradation products of lignin from wheat straw better than those from kenaf lignin, based on the amount of low-molecular-weight products left in solution.     

Progress in biopulping of non-woody materials: Chemical, enzymatic and ultrastructural aspects of wheat straw delignification with ligninolytic fungi from the genus Pleurotus

Abstract: During screening of basidiomycetes for wheat straw delignification, considerable lignin degradation with a limited attack to cellulose was attained with Pleurotus eryngii . Straw solid-state fermentation (SSF) was optimized, and the enzymatic mechanisms for lignin degradation were investigated. No lignin peroxidase was detected under liquid or SSF conditions, but high laccase and aryl-alcohol oxidase levels were found. The latter enzyme has been fully characterized in PI. eryngii and it seems to be involved in a cyclic redox system for H₂0₂ generation from aromatic compounds. Results obtained using homoveratric acid suggest that Pleurotus laccase could be involved in degradation of phenolic and non-phenolic lignin moieties. Histological and ultrastructural studies provided some general morphological characteristics of the fungal attack on wheat straw. Whereas a simultaneous degradation pattern was observed in straw treated with Phanerochaete chrysosporium , PI. eryngii caused partial degradation of middle lamella and separation of individual sclerenchymatic fibers. When these straw samples were subjected to refining tests, energy saving after biological treatment was the highest in the case of straw treated with PI. eryngii , which also produced the lowest substrate loss. From these results, a correlation between preferential removal of lignin, separation of sclerenchymatic fibers and pulping properties was provided during fungal treatment of wheat straw.     

Solid-state fermentation of natural birch lignin by Phanerochaete chrysosporium

A strain of white rot fungus, Phanerochaete chrysosporium Burds. ME446, has been characterized with respect to the extent and rate of Betula nigrificans lignin and non-lignin conversion by solid-substrate fermentation for different culture conditions. Moisture content, inoculum density, nitrogen supplementation and autoclaving of birch solids significantly affected lignin conversion rates and yields in 20 day fermentations. Oxygen favoured lignin over non-lignin conversion at partial pressures of 1.0 atm. Oxygen pressures of 2.0 atm severely inhibited both lignin and non-lignin conversions. Carbon dioxide partial pressures of 0.25, 0.5 and 1.0 atm at oxygen pressures of 1.0 atm increasingly inhibited both lignin and non-lignin conversion rates and yields. The results of these studies demonstrate the effects of major process variables and suggest a need to control the gas environment for process optimization.     

The response of wheat straw varieties to mild sulphur dioxide treatment

Straws of five wheat cultivars, including soft and hard and dwarf and semi-dwarf varieties, were treated with sulphur dioxide (SO₂), and the effect of treatment on monosaccharide composition and cell wall (CW) degradation by rumen microorganisms was studied. Despite agrobotanical differences, the monosaccharide profiles of the straw hydrolysates were similar. Glucose, xylose, uronic acids and arabinose comprised about 98% of the total monosaccharides and the ratio of glucose to xylose was generally 2:1. The major and general effect of SO₂ treatment was expressed in solubilization of the matrix polysaccharides, cellulose being hardly affected. More than 20% of the permanganate lignin was solubilized by SO₂ in four of the cultivars. The ‘Lakhish’ cultivar had the highest lignin content (13.3%), but its lignin proved resistent to SO₂ treatment. Organic matter digestibility in vitro (IVD) was maximally increased in four varieties (excluding the ‘Lakhish’ straw) to 77–84%, and the IVD of monosaccharides to 88–93%. The treatment effect on the ‘Lakhish’ variety was weaker, the IVD of organic matter and monosaccharides was only increased to 67 and 77%, respectively. Other straw batches of the ‘Lakhish’ variety have shown a strong response to SO₂ treatment similar to that found in the straw batches of the other four cultivars. The present study provides support to previous conclusions about the major biodegradation obstacles in wheat straw. The results of this study imply that mild SO₂ treatment is generally effective in increasing the degradability of wheat straw by rumen microorganisms.     

Biodelignification of wheat straw by different fungal associations

Seven strains of fungi were tested individually as well as in different combinations to determine their lignin degrading ability using wheat straw as natural substrate. When tested individuallyPhanerochaete chrysosporium caused a maximum loss in total organic matter (26.45%) as well as in the lignin component (28.93%). The associations between different groups: white-rot plus white-rot, white-rot plus brown-rot and white-rot plus soft-rot fungi revealed that in certain combinations the ligninolysis was enhanced to variable extent.Deadalea flavida plusP. chrysosporium was the best association to bring about a lignin loss of 36.27%.     

Production of Manganese Peroxidase and Organic Acids and Mineralization of 14C-Labelled Lignin (14C-DHP) during Solid-State Fermentation of Wheat Straw with the White Rot Fungus Nematoloma frowardii

The basidiomycetous fungus Nematoloma frowardii produced manganese peroxidase (MnP) as the predominant ligninolytic enzyme during solid-state fermentation (SSF) of wheat straw. The purified enzyme had a molecular mass of 50 kDa and an isoelectric point of 3.2. In addition to MnP, low levels of laccase and lignin peroxidase were detected. Synthetic ¹⁴C-ring-labelled lignin (¹⁴C-DHP) was efficiently degraded during SSF. Approximately 75% of the initial radioactivity was released as ¹⁴CO₂, while only 6% was associated with the residual straw material, including the well-developed fungal biomass. On the basis of this finding we concluded that at least partial extracellular mineralization of lignin may have occurred. This conclusion was supported by the fact that we detected high levels of organic acids in the fermented straw (the maximum concentrations in the water phases of the straw cultures were 45 mM malate, 3.5 mM fumarate, and 10 mM oxalate), which rendered MnP effective and therefore made partial direct mineralization of lignin possible. Experiments performed in a cell-free system, which simulated the conditions in the straw cultures, revealed that MnP in fact converted part of the ¹⁴C-DHP to ¹⁴CO₂ (which accounted for up to 8% of the initial radioactivity added) and ¹⁴C-labelled water-soluble products (which accounted for 43% of the initial radioactivity) in the presence of natural levels of organic acids (30 mM malate, 5 mM fumarate).     

Composting of poultry manure and wheat straw in a closed reactor: optimum mixture ratio and evolution of parameters

The main objectives of this work were to investigate the evolution of some principal physico-chemical properties (temperature, carbon dioxide, oxygen, ammonia, pH, electrical conductivity, organic matter) and microbial population (mesophilic and thermophilic bacteria and fungi) during composting poultry manure with wheat straw in a reactor system, and to evaluate the optimum mixture ratio for organic substrate production. The experiments were carried out in four small laboratory reactors (1 l) and one large reactor (32 l) under adiabatic conditions over 14 days. During the process the highest temperature was 64.6°C, pH varied between 7.40 and 8.85, electrical conductivity varied between 3.50 and 4.31 dS m⁻¹ and the highest value of organic matter (dry weight) degradation was 47.6%. Mesophilic bacteria and fungi predominated in the beginning, and started the degradation with generation of metabolic heat. By increasing the temperature in reactors, the number of thermophilic microorganisms also increased, which resulted in faster degradation of substrate. The application of a closed reactor showed a rapid degradation of manure/straw mixture as well as a good control of the emissions of air polluting gases into atmosphere. The results showed that the ratio of manure to straw 5.25:1 (dry weight) was better for composting process than the other mixture ratios.     

Decomposition of Lignocellulose by Cyathus stercoreus (Schw.) de Toni NRRL 6473, a “White Rot” Fungus from Cattle Dung

Cyathus stercoreus (Schw.) de Toni NRRL 6473, isolated from aged and fragmented cattle dung collected from a Michigan pasture, effected substantial losses in lignin (45%) from wheat straw during a 62-day fermentation (25°C). The basidiomycete also improved wheat straw digestibility by freeing α-cellulose for enzymatic hydrolysis to glucose (230 mg of glucose per 1,000 mg of fermented residue). The rationale for selecting C. stercoreus in attempting to biologically modify the lignin and cellulose components in wheat straw or other gramineous agricultural residues was based on the expectation that this organism is ecologically specialized to enzymatically attack the substructures of native lignins in grasses.     

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     

Biodegradation of paddy straw obtained from different geographic locations by means of <Emphasis Type="Italic">Phlebia</Emphasis> spp. for animal feed

Various cereal straws are used as feed by supplementing the green forage or other feed stuffs. An experiment was designed to see the effect of different geographic locations and climatological conditions on biochemical constituents, fungal degradation and in vitro digestibility of paddy straw. Paddy straw (PS) obtained from three different geographic locations of India was subjected to solid state fermentation using four white rot fungi i.e. Phlebia brevispora, P. fascicularia, P. floridensis and P. radiata. Changes in the biochemical constituents like water soluble content, hemicellulose, cellulose, lignin, total organic matter, and in vitro digestibility of paddy straw was analyzed over a period of 60 days along with lignocellulolytic enzymes i.e. laccase, xylanase and carboxymethyl cellulase. All the fungi degraded the straw samples and enhanced the in vitro digestibility. The paddy straw, obtained from north western zone (NWZ) suffered a maximum loss (228 g/kg) of lignin by P. radiata, while a maximum enhancement of in vitro digestibility from 185 to 256 g/kg was achieved by P. brevispora, which also caused minimum loss in total organic matter (98 g/kg). In PS obtained from central eastern zone (CEZ) and north eastern zone (NEZ), a maximum amount of lignin (210 and 195 g/kg, respectively) was degraded by P. floridensis and resulted into a respective enhancement of in vitro digestibility from 172 to 246 g/kg and 188 to 264 g/kg. The study demonstrates that geographic locations not only affect the biochemical constituents of paddy straw but the fungal degradation of fibers, their in vitro digestibility and lignocellulolytic enzyme activity of the fungus may also vary.