Screening of white‐rot fungi for bioprocessing of wheat straw into ruminant feed

Novel techniques for the mass production of nutritionally improved, fungus-treated lignocellulosic biomass for ruminant nutrition

BACKGROUND

Laboratory-scale experiments have shown that treatment with selective lignin-degrading white-rot fungi improves the nutritional value and ruminal degradability of lignocellulosic biomass (LCB). However, the lack of effective field-applicable pasteurization methods has long been recognized as a major obstacle for scaling up the technique for fungal treatment of large quantities of LCB for animal feeding. In this study, wheat straw (an LCB substrate) was subjected to four field-applicable pasteurization methods - hot-water, formaldehyde fumigation, steam, and hydrated lime - and cultured with Pleurotus ostreatus grain spawn for 10, 20, and 30 days under solid-state fermentation. Samples of untreated, pasteurized but non-inoculated and fungus-treated straws were analyzed for chemical composition, aflatoxin B1 (AFB1 ), and in vitro dry matter digestibility (IVDMD), in vitro total gas (IVGP), methane (CH4 ), and volatile fatty acid (VFA) production.

RESULTS

During the 30-day fungal treatment, steam and lime pasteurized straws had the greatest loss of lignin, resulting in marked improvements in crude protein (CP), IVDMD, IVGP, and total VFAs. Irrespective of the pasteurization method, the increase in IVDMD during fungal treatment was linearly (R2  = 0.77-0.92) related to lignin-loss in the substrate during fungal treatment. The CH4 production of the fungus-treated straw was not affected by the pasteurization methods. Aflatoxin B1 was within the safe level (<5 μg kg-1 ) in all pasteurized, fungus treated straws.

CONCLUSION

Steam and lime were promising field-applicable pasteurization techniques to produce nutritionally improved fungus-treated wheat straw to feed ruminants. Lime pasteurization was more economical and did not require expensive energy inputs. © 2023 Society of Chemical Industry.

A Glycosyl Hydrolase 30 Family Xylanase from the Rumen Metagenome and Its Effects on In Vitro Ruminal Fermentation of Wheat Straw

The challenge of wheat straw as a ruminant feed is its low ruminal digestibility. This study investigated the impact of a xylanase called RuXyn, derived from the rumen metagenome of beef cattle, on the in vitro ruminal fermentation of wheat straw. RuXyn encoded 505 amino acids and was categorized within subfamily 8 of the glycosyl hydrolase 30 family. RuXyn was heterologously expressed in Escherichia coli and displayed its highest level of activity at pH 6.0 and 40 °C. RuXyn primarily hydrolyzed xylan, while it did not show any noticeable activity towards other substrates, including carboxymethylcellulose and Avicel. At concentrations of 5 mM, Mn2+ and dithiothreitol significantly enhanced RuXyn's activity by 73% and 20%, respectively. RuXyn's activity was almost or completely inactivated in the presence of Cu2+, even at low concentrations. The main hydrolysis products of corncob xylan by RuXyn were xylopentose, xylotriose, and xylotetraose. RuXyn hydrolyzed wheat straw and rice straw more effectively than it did other agricultural by-products. A remarkable synergistic effect was observed between RuXyn and a cellulase cocktail on wheat straw hydrolysis. Supplementation with RuXyn increased dry matter digestibility; acetate, propionate, valerate, and total volatile fatty acid yields; NH3-N concentration, and total bacterial number during in vitro fermentation of wheat straw relative to the control. RuXyn's inactivity at 60 °C and 70 °C was remedied by mutating proline 151 to phenylalanine and aspartic acid 204 to leucine, boosting activity to 20.3% and 21.8% of the maximum activity at the respective temperatures. As an exogenous enzyme preparation, RuXyn exhibits considerable potential to improve ruminal digestion and the utilization of wheat straw in ruminants. As far as we know, this is the first study on a GH30 xylanase promoting the ruminal fermentation of agricultural straws. The findings demonstrate that the utilization of RuXyn can significantly enhance the ruminal digestibility of wheat straw by approximately 10 percentage points. This outcome signifies the emergence of a novel and highly efficient enzyme preparation that holds promise for the effective utilization of wheat straw, a by-product of crop production, in ruminants.

Green chemical and hybrid enzymatic pretreatments for lignocellulosic biorefineries: Mechanism and challenges

The greener chemical and enzymatic pretreatments for lignocellulosic biomasses are portraying a crucial role owing to their recalcitrant nature. Traditional pretreatments lead to partial degradation of lignin and hemicellulose moieties from the pretreated biomass. But it still restricts the enzyme accessibility for the digestibility towards the celluloses and the interaction of lignin-enzymes, nonproductively. Moreover, incursion of certain special chemical treatments and other lignin sulfonation techniques to the enzymatic pretreatment (hybrid enzymatic pretreatment) enhances the lignin structural modification, solubilization of the hemicelluloses and both saccharification and fermentation processes (SAF). This article concentrates on recent developments in various chemical and hybrid enzymatic pretreatments on biomass materials with their mode of activities. Furthermore, the issues on strategies of the existing pretreatments towards their industrial applications are highlighted, which could lead to innovative ideas to overcome the challenges and give guideline for the researchers towards the lignocellulosic biorefineries.

Response surface methodology for the mixed fungal fermentation of Codonopsis pilosula straw using Trichoderma reesei and Coprinus comatus

The objective of this study was to investigate the cellulose degradation rate (CDR) and lignin degradation rate (LDR) of Codonopsis pilosula straw (CPS) and the optimal fermentation parameters for mixed fungal fermentation. Single-factor tests were used to study the effects of the fungal ratio (Trichoderma reesei: Coprinus comatus), fungal inoculum, corn flour content, and fermentation time on the degradation rate of cellulose and lignin. Based on the results of this experiment, the optimal fermentation factors were identified, and the effects of various factors and their interactions on the degradation rates of cellulose and lignin were further evaluated using the response surface method. The quadratic polynomial mathematical model of degradation rates of the cellulose and lignin in CPS by mixed fungus fermentation was established using Design Expert software v8.0.6. Under the optimal parameters for fungal fermentation of CPS straw (fungal ratio 4:6, fungal inoculum 8%, corn flour content 10%, fermentation time of 15 d), the CDR and LDR reached 13.65% and 10.73%, respectively. Collectively, the mixed fungal fermentation of CPS resulted in decreased lignin and cellulose content, better retention of nutrients, and enhanced fermentation quality. The results of this study indicate that fermentation using Trichoderma reesei and Coprinus comatus is a productive method for straw degradation, providing a theoretical basis for the development of CPS as feed.

Effects of the Incubation Period of Pleurotus ostreatus on the Chemical Composition and Nutrient Availability of Solid-State-Fermented Corn Stover

The current study aimed to optimize and improve the feeding value of Pleurotus ostreatus-fermented corn stover by evaluating the effects of five solid-state fermentation times and three in vitro fermentation periods on the chemical composition, dry matter disappearance (DMD), microbial mass and volatile fatty acid (VFA) production of treated and untreated corn stover. The study utilized a 3 × 5 factorial design, with eight replicates per treatment. Dry matter, crude protein (CP), ash and non-fiber carbohydrate (NFC) contents increased quadratically (p < 0.05) with increases in the solid-state fermentation time. Increases of 44.4-59.1%, 20.6-78.6% and 40.5-121% were noted for the CP, ash and NFC contents, respectively. Organic matter, ether extract, neutral detergent fiber and hemicellulose contents decreased quadratically (p < 0.05) across the treatments. Similar trends were noted for DM and fiber disappearance in the treatments. The total gas production and in vitro true dry matter digestibility (IVTDMD) increased quadratically, while microbial mass and in vitro apparent DMD increased in a linear manner. The total VFA, propionate and butyrate contents increased linearly. Both the acetate content and the A:P ratio decreased in a linear manner. The results show that the rumen fermentation pathway favors the production of propionate, with increases in propionate production of 7.46 and 8.30% after 2 and 4 wk, respectively. The study showed that a 2 wk period of solid-state fermentation is sufficient to provide a bio-transformed cow-calf feed resource from P. ostreatus-treated corn stover.

In vitro ruminal degradability of wheat straw cultivated with white-rot fungi adapted to mushroom farming conditions

Biological treatment of cereal straw for ruminant nutrition purposes might present an environmentally friendly option of valorizing a widely available by-product of grain production for farming systems with low external input. Several strains of white-rot fungi have been selected in the past under mostly controlled laboratory conditions for their capacity of lignin degradation. The study adapted to conditions on farm for upscaling purposes. The development of the in vitro straw digestibility with two different moistening pre-treatments and inoculated with three different fungi species, namely Pleurotus ostreatus, Ceriporiopsis subvermispora and Volvariella volvacea, was determined up to 42 days of fermentation with five sampling times. The effect of physical straw pre-treatments on nutritional parameters was evaluated. The neutral detergent fiber digestibility (NDFD_30h), enzymatically soluble organic substance (ELOS) and the gas production (Hohenheim Feed value Test, HFT) as indicators for in vitro ruminal degradability decreased over time independent of the fungus: HFT, ELOS and NDFD_30h by up to 50, 35 and 30% of the original straw. Remoistening and autoclaving the straw increased the gas production significantly by 2.6 mL/200 g dry matter (DM), and ELOS and NDFD_30h by 45 and 51 g/kg DM compared to the original straw (34.9 mL/200 mg DM, 342 g/kg DM, 313 g/kg NDF).

Effects of Solid-State Fermentation Pretreatment with Single or Dual Culture White Rot Fungi on White Tea Residue Nutrients and In Vitro Rumen Fermentation Parameters

Fermentation of agricultural by-products by white rot fungi is a research hotspot in the development of ruminant feed resources. The aim of this study was to investigate the potential of the nutritional value and rumen fermentation properties of white tea residue fermented at different times, using single and dual culture white rot fungal species. Phanerochaete chrysosporium, Pleurotus ostreatus, and Phanerochaete chrysosporium + Pleurotus ostreatus (dual culture) solid-state fermented white tea residue was used for 4 weeks, respectively. The crude protein content increased significantly in all treatment groups after 4 weeks. Total extractable tannin content was significantly decreased in all treatment groups (p < 0.01). P. chrysosporium and dual culture significantly reduced lignin content at 1 week. The content of NH3-N increased in each treatment group (p < 0.05). P. chrysosporium treatment can reduce the ratio of acetic to propionic and improve digestibility. Solid state fermentation of white tea residue for 1 week using P. chrysosporium was the most desirable.

Hematological Changes in Sika Doe and Suckling Fawn Fed with Spent Mushroom Substrate of Pleurotus ostreatus

Sika deer velvet antler is the most important animal nutraceutic in traditional Chinese medicine. Reducing the breeding cost of sika deer by looking for a low-cost diet is the main research direction at present. The purpose of this experiment was to find an alternative diet for sika deer and reduce the cost of the diet by using spent mushroom substrate (SMS) as a concentrate supplement. The apparent digestibility for sika doe and the hematological changes of sika doe and suckling fawn were measured by replacing 10% of the concentrate supplement with SMS of Pleurotus ostreatus (SMS-MP). Compared with the control group, the digestibility of dry matter (DM), total protein (TP), globulin (GLO), and cholesterol (CHOL) of sika doe were significantly decreased (p < 0.05), and glucose (GLU), alanine (Ala), phenylalanine (Phe), and proline (Pro) of sika doe were significantly increased (p < 0.05) after the replacement of SMS-MP. Compared with the control group, the serum GLU of suckling fawn was significantly decreased (p < 0.05) and the phosphatase (ALP) was significantly increased after the replacement of SMS-MP (p < 0.05). There were no significant differences in the immune globulin and amino acid of suckling fawns between the two groups (p > 0.05). The present findings confirm the applicability of SMS-MP as a sika doe concentrate supplement. At the same time, using SMS, a waste resource, can not only reduce the breeding cost of sika doe, but also make full use of SMS to reduce environmental pollution.

Effect of Ammoniated and/or Basidiomycete White-Rot Fungi Treatment on Rice Straw Proximate Composition, Cell Wall Component, and In Vitro Rumen Fermentation Characteristics

Various pretreatments are employed to increase the utilization of rice straw as a ruminant feed ingredient to minimize its negative environmental impact. However, an efficient alternative is still needed. The purpose of this study was to evaluate the ability of ammonia and/or white-rot fungi (Pleurotus ostreatus) to degrade lignin, increase the nutritional value, and enhance the rumen fermentability of rice straw. Rice straw was treated with ammonia and/or basidiomycete white-rot fungi (P. ostreatus) with untreated straw as control under solid-state fermentation employing a completely randomized design. The crude protein increased from 2.05% in the control to 3.47% in ammoniated rice straw, 5.24% in basidiomycete white-rot fungi (P. ostreatus), and 6.58% in ammoniated-basidiomycete white-rot fungi-treated (P. ostreatus) rice straw. The ammoniated-basidiomycete white-rot fungi-treated (P. ostreatus) rice straw had the least lignin content (3.76%). Ammoniated-basidiomycete white-rot fungi-treated (P. ostreatus) rice straw had improved in vitro dry matter digestibility (65.52%), total volatile fatty acid (76.56 mM), and total gas production (56.78 mL/g) compared to ammoniated rice straw (56.16%, 67.71 mM, 44.30 mL/g) or basidiomycete white-rot fungi-treated (P. ostreatus) rice straw (61.12%, 75.36 mM, 49.31 mL/g), respectively. The ammoniated-basidiomycete white-rot fungi (P. ostreatus) treatment improved rice straw’s nutritional value, in vitro dry matter digestibility, volatile fatty acids, and gas production.

Improving crude protein and methionine production, selective lignin degradation and digestibility of wheat straw by Inonotus obliquus using response surface methodology

BACKGROUND

To date, fungus-assisted pretreatment of agricultural residue has not become the preferred method to produce protein-enriched and ruminally digestible animal feed because of low time efficiency of fungal delignification and protein production, i.e. the long solid-state fermentation period, and because of laccase as a potential inhibitor of cellulose activity. In this study, response surface methodology was employed to optimize the parameters in the process of producing nutritious animal feed from wheat straw with Inonotus obliquus pretreatment.

RESULTS

The mineral salt solution containing (w/v) (NH₄ )₂ SO₄ 1%, MgSO₄ ·7H₂ O 0.03%, KH₂ PO₄ 0.011%, Tween-80 0.4%, and corn starch 10% with pH of 7.4 was optimized. Inonotus obliquus rapidly and completely colonized on wheat straw with an ergosterol content of 280 μg g^-1 dry matter, consuming 45% of lignin after 15 days of fermentation, producing maximums of lignin peroxidase (1729 IU g^-1 ), manganese peroxidase (610 IU g^-1 ) and laccase (98 IU g^-1 ) on days 5, 15, and 25, respectively. The crude protein (102.4 g kg^-1 ) of 15-day fermented wheat straw increased by ~132%. After hydrolysis, the essential protein-bound amino acids (15.3 g kg^-1 ) increased by ~47%, within which Met and Lys measured ~1070% and ~60% higher. The treatment with I. obliquus also improved the in vitro gas production after 72 h (IVGP₇₂ ) of wheat straw to 178.8 mL g^-1 organic matter (~43% increase).

CONCLUSION

For the first time, we found that I. obliquus is an effective white rot fungus turning wheat straw into ruminally digestible animal feed without laccase inhibitor.

Treatment of Rice Stubble with Pleurotus ostreatus and Urea Improves the Growth Performance in Slow-Growing Goats

Simple Summary

Fungi treatment is well established as a promising approach to upgrade the nutritional value of lignocellulosic biomass. This potency of fungi treatment is, however, primarily based on in vitro experiments, and extrapolation to practice is currently hindered, owing to a dearth of studies addressing the practical relevance of fungal treatment of high-fiber feed, such as rice straw and rice stubble. These potential biomasses are rife in Southeast Asian countries, coinciding with increasing rice production; however, it remains a big challenge to utilize rice stubble as a potential feed for ruminants. Similar to rice straw, rice stubble is traditionally eliminated through controlled burning, which is harmful to the environment. The aim of this study was to convert rice stubble into a new animal feed capable of increasing environmental friendliness. Using urea, it is well known to modify the lignification or silicification of lignocellulosic biomass. However, it remains scanty in combination with fungi treatment. Therefore, we treated rice stubble with either urea or oyster fungus (Pleurotus ostreatus) or a combination of these two treatments and offered these treated rice stubbles to slow-growing goats with the objective to study their effect on feed intake, digestibility, and fermentation end-products.

Abstract

The objective of this study was to evaluate the efficacy of the fungal treatment (Pleurotus ostreatus) of urea-treated rice stubble on growth performance in slow-growing goats. Eighteen crossbred Thai-native x Anglo-Nubian male goats (average body weight: 20.4 ± 2.0 kg) were randomly assigned to three experimental total mixed rations containing 35% rice stubble (RS) that were either untreated (URS), urea treated (UTRS), or treated with urea and fungi (UFTRS). URS and UTRS were cultivated and harvested from an aseptically fungal spawn, incubated at 25–30 °C for 25 days. Indicators of growth performance were monitored, and feces were collected quantitatively to assess nutrient digestibility, during a 12-week feeding trial. All goats remained healthy throughout the experiment. The goats fed UFTRS had a lower feed conversion ratio (kg feed/kg growth) compared to goats fed URS or UTRS. Compared to URS, dietary UFTRS increased the nutrient digestibility of slow-growing goats, such as organic matter (OM) (+8.5%), crude protein (CP) (+5.5%), neutral detergent fiber (NDF) (+39.2%), and acid detergent fiber (ADF) (+27.4%). Likewise, dietary UFTRS tended to increase rumen ammonia concentrations, but rumen pH and volatile fatty acids were not affected by UFTRS. In conclusion, the present study indicates that the fungal treatment of RS is an effective tool to improve the growth performance of slow-growing goats.

Feeding Fungal-Pretreated Corn Straw Improves Health and Meat Quality of Lambs Infected with Gastrointestinal Nematodes

Simple Summary

Non-chemical strategies to control gastrointestinal nematode (GINs) infections are urgently needed to support the sustainable development of the livestock industry. The potential anti-parasitic properties in fungal-pretreated corn straw on health and meat quality of lambs infected with GINs were investigated in this study. In summary, feeding fungal-pretreated corn straw improved health and meat quality, including meat color and tenderness. Improved meat traits were attributed to fungal-pretreated corn straw providing additional dietary protein for lambs and secreting some nematicidal metabolites to repel GINs, which increased PCV and plasma iron content of lambs and reversed negative effects of GINs on meat quality.

Abstract

Infections with gastrointestinal nematodes (GIN) adversely affect meat color in lambs. Although white-rot fungi (WRF) pretreatment increases nutritional value and fiber digestion of corn straw for lambs, whether it can improve meat quality of lambs infected with GINs is unknown. The objective of this experiment was to study effects of feeding WRF-pretreated corn straw on the health and meat quality of lambs infected with GINs. Sixteen healthy Ujumqin lambs were orally drenched with 3rd-stage GINs larvae and randomly divided into two dietary treatments of control (CON) and WRF diets for 70 days of feeding. Results showed that feeding WRF-pretreated corn straw decreased L* and b* values (p < 0.05) and increased a* value (p < 0.01) of both longissimus thoracis et lumborum (LTL) and semimembranosus (SM) muscles of lambs infected with GINs. Feeding WRF-pretreatment corn straw decreased fecal egg count (p = 0.014) and increased packed cell volume (p = 0.013) of lambs from 28 d of feeding and increased plasma iron content (p = 0.008) of lambs from 56 d of the feeding. Feeding WRF-pretreatment corn straw decreased myosin heavy-chain (MyHC)-I (p = 0.032) and MyHC-IIα (p = 0.025) content in LTL muscle and MyHC-I (p = 0.022) and MyHC-IIβ (p = 0.048) in SM muscle of lambs. In conclusion, although there were no significant changes in the content of most amino acids or increased intensity of better flavor compounds, meat quality and health of lambs infected with GINs was significantly improved by feeding WRF-pretreated corn straw due to increased PCV and meat color and tenderness.

Evaluating the effects of storage conditions on dry matter loss and nutritional quality of grain legume fodders in West Africa

•

Nutritional quality and dry matter quantity of grain legume fodders (GLFs) declined with increasing duration of storage.

•

GLFs stored in sacks had better nutritional quality and less dry matter loss than stored GLFs tied with rope.

•

Decline in nutritional quality is drastic in leaf fractions than in stem fractions of GLFs during storage.

•

Aflatoxin was not detected in groundnut fodder during storage in the dry season.

Feed scarcity is a major challenge for livestock production in West Africa, especially during the dry season when grass quality and quantity on grazing lands are inadequate. In the dry season, crop residues are a key source of livestock feed. The residues of grain legumes, also known as grain legume fodders (GLFs), are stored and traded for feeding in the dry season. The objectives of our experiment were to evaluate the effects of storage conditions and duration on dry matter (DM) and nutritional quality of GLFs, and to assess the risk of aflatoxin in stored groundnut fodder. The experiment was designed as a factorial trial with 18 treatment combinations with four replicates (4 farms). The treatments included: 3 types of GLFs (cowpea, groundnut and soybean fodder), 3 types of storage locations (rooftop, room and tree-fork) and 2 types of packaging (packed in polythene sacks and unpacked but tied with rope). Over a 120 day storage period, DM quantity reduced by an average of 24 % across all storage conditions, showing a range from 14 % in the best condition (sacks and rooms) to 35 % in the worst condition (bundles tied with rope and stored on rooftops or tree-forks). Soybean fodder had no leaves, the lowest crude protein content (CP) and organic matter digestibility (OMD), and the highest content of cell wall components compared to cowpea and groundnut fodder. These nutritional quality parameters in soybean fodder hardly changed during storage. Cowpea and groundnut fodder showed a decrease in leaf-to-stem ratio (LSR), CP and OMD, and an increase in the content of cell wall components during storage, but their nutritional value remained better than that of soybean fodder. Storage in sacks resulted in less DM loss, in less reduction of LSR and in a smaller increase of the content of cell wall components than storage of bundles tied with rope. Our study shows that the DM loss, the decrease in LSR, and the increase in the content of cell wall components can be prevented partly by storing GLFs in sacks instead of tying bundles with rope, and to a minor extent by storing in rooms instead of in the open air. Aflatoxin was not detectable in the groundnut fodder samples. Our results highlight that attention to storage conditions can improve the feeding value of GLFs which are key for livestock nutrition during the dry season.

Structural Motifs of Wheat Straw Lignin Differ in Susceptibility to Degradation by the White-Rot Fungus Ceriporiopsis subvermispora

The white-rot fungus Ceriporiopsis subvermispora delignifies plant biomass extensively and selectively and, therefore, has great biotechnological potential. We previously demonstrated that after 7 weeks of fungal growth on wheat straw 70% w/w of lignin was removed and established the underlying degradation mechanisms via selectively extracted diagnostic substructures. In this work, we fractionated the residual (more intact) lignin and comprehensively characterized the obtained isolates to determine the susceptibility of wheat straw lignin's structural motifs to fungal degradation. Using 13C IS pyrolysis gas chromatography-mass spectrometry (py-GC-MS), heteronuclear single quantum coherence (HSQC) and 31P NMR spectroscopy, and size-exclusion chromatography (SEC) analyses, it was shown that β-O-4' ethers and the more condensed phenylcoumarans and resinols were equally susceptible to fungal breakdown. Interestingly, for β-O-4' ether substructures, marked cleavage preferences could be observed: β-O-4'-syringyl substructures were degraded more frequently than their β-O-4'-guaiacyl and β-O-4'-tricin analogues. Furthermore, diastereochemistry (threo > erythro) and γ-acylation (γ-OH > γ-acyl) influenced cleavage susceptibility. These results indicate that electron density of the 4'-O-coupled ring and local steric hindrance are important determinants of oxidative β-O-4' ether degradation. Our findings provide novel insight into the delignification mechanisms of C. subvermispora and contribute to improving the valorization of lignocellulosic biomass.

Modification of corn stover for improving biodegradability and anaerobic digestion performance by Ceriporiopsis subvermispora

Ceriporiopsis subvermispora was used to modify corn stover for improving the biodegradability and biomethane yield. Corn stover was incubated with C. subvermispora for 5-90 days then anaerobically digested. It was found that the corn stover modified for 15 days achieved the highest biomethane yield of 235 mL·g^-1 VS, which was an increase of 15.2% over that of the non-modified one. The mechanism analyses indicated that the improvement resulted from the combined roles of degradation selectivity, destruction of lignocellulosic structures, and linkages. The analyses showed that C. subvermispora has a high relative selectivity of lignin degradation. The structure of the lignin and the linkages among lignin and hemicellulose and cellulose were broken obviously by acetyl group removal, and the enzymatic hydrolysis of cellulose was increased by 35.61%. The finding indicated that C. subvermispora modification is one of the effective methods for enhancing biomethane yield of corn stover.

Stable and transient transformation, and a promoter assay in the selective lignin-degrading fungus, Ceriporiopsis subvermispora

A genetic transformation system was developed for the selective white rot basidiomycete Ceriporiopsis subvermispora using a modified protocol with polyethylene glycol and CaCl₂ treatment of the protoplasts and plasmids harboring recombinant hygromycin phosphotransferase (hph) driven by a homologous promoter. During repeated transfer on fresh potato dextrose agar plates containing 100 µg/ml hygromycin B, most transformants lost drug resistance, while the remaining isolates showed stable resistance over five transfers. No drug-resistant colonies appeared in control experiments without DNA or using a promoter-less derivative of the plasmid, indicating that a transient expression of the recombinant hph was driven by the promoter sequence in these unstable drug-resistant transformants. Southern blot analysis of the stable transformants revealed random integration of the plasmid DNA fragment in the chromosome at different copy numbers. This transformation system yielding mostly transient transformants was successfully used for promoter assay experiments, and only a 141-bp fragment was found to be essential for the basic promoter function of glyceraldehyde dehydrogenase gene (gpd) in this fungus. Subsequent mutational analyses suggested that a TATAA sequence is important for the basic promoter function of gpd gene. The promoter assay system will enable the functional analysis of gene expression control sequences quickly and easily, mostly in the absence of undesirable effects from differences in copy number and chromosomal position of an integrated reporter gene among stable transformants.

Evaluation of fungal degradation of wheat straw cell wall using different analytical methods from ruminant nutrition perspective

BACKGROUND

White rot fungi have been used to improve the nutritive value of lignocellulose for ruminants. In feed analysis, the Van Soest method is widely used to determine the cell wall contents. To assess the reliability of this method (Method A) for determination of cell wall contents in fungal-treated wheat straw, we compared a combined monosaccharide analysis and pyrolysis coupled to gas chromatography with mass spectrometry (Py-GC/MS) (Method B). Ruminal digestibility, measured as in vitro gas production (IVGP), was subsequently used to examine which method explains best the effect of fungal pretreatment on the digestibility of wheat straw.

RESULTS

Both methods differed considerably in the mass recoveries of the individual cell wall components, which changed on how we assess their degradation characteristics. For example, Method B gave a higher degradation of lignin (61.9%), as compared to Method A (33.2%). Method A, however, showed a better correlation of IVGP with the ratio of lignin to total structural carbohydrates, as compared to Method B (Pearson's r of -0.84 versus -0.69). Nevertheless, Method B provides a more accurate quantification of lignin, reflecting its actual modification and degradation. With the information on the lignin structural features, Method B presents a substantial advantage in understanding the underlying mechanisms of lignin breakdown. Both methods, however, could not accurately quantify the cellulose contents - among others, due to interference of fungal biomass.

CONCLUSION

Method A only accounts for the recalcitrant residue and therefore is more suitable for evaluating ruminal digestibility. Method B allows a more accurate quantification of cell wall, required to understand and better explains the actual modification of the cell wall. The suitability of both methods, therefore, depends on their intended purposes. © 2019 The Authors. Journal of The Science of Food and Agriculture published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Symposium review: Technologies for improving fiber utilization

The forage lignocellulosic complex is one of the greatest limitations to utilization of the nutrients and energy in fiber. Consequently, several technologies have been developed to increase forage fiber utilization by dairy cows. Physical or mechanical processing techniques reduce forage particle size and gut fill and thereby increase intake. Such techniques increase the surface area for microbial colonization and may increase fiber utilization. Genetic technologies such as brown midrib mutants (BMR) with less lignin have been among the most repeatable and practical strategies to increase fiber utilization. Newer BMR corn hybrids are better yielding than the early hybrids and recent brachytic dwarf BMR sorghum hybrids avoid lodging problems of early hybrids. Several alkalis have been effective at increasing fiber digestibility. Among these, ammoniation has the added benefit of increasing the nitrogen concentration of the forage. However, few of these have been widely adopted due to the cost and the caustic nature of the chemicals. Urea treatment is more benign but requires sufficient urease and moisture for efficacy. Ammonia-fiber expansion technology uses high temperature, moisture, and pressure to degrade lignocellulose to a greater extent than ammoniation alone, but it occurs in reactors and is therefore not currently usable on farms. Biological technologies for increasing fiber utilization such as application of exogenous fibrolytic enzymes, live yeasts, and yeast culture have had equivocal effects on forage fiber digestion in individual studies, but recent meta-analyses indicate that their overall effects are positive. Nonhydrolytic expansin-like proteins act in synergy with fibrolytic enzymes to increase fiber digestion beyond that achieved by the enzyme alone due to their ability to expand cellulose microfibrils allowing greater enzyme penetration of the cell wall matrix. White-rot fungi are perhaps the biological agents with the greatest potential for lignocellulose deconstruction, but they require aerobic conditions and several strains degrade easily digestible carbohydrates. Less ruminant nutrition research has been conducted on brown rot fungi that deconstruct lignocellulose by generating highly destructive hydroxyl radicals via the Fenton reaction. More research is needed to increase the repeatability, efficacy, cost effectiveness, and on-farm applicability of technologies for increasing fiber utilization.

Improving ruminal digestibility of various wheat straw types by white-rot fungi

BACKGROUND

This study investigated the ruminal degradability of various wheat straw types by the white-rot fungi Ceriporiopsis subvermispora (CS) and Lentinula edodes (LE). Different cultivars (CV) of wheat straw at different maturity stages (MS) were treated with the fungi for 7 weeks and assessed for chemical composition and in vitro gas production (IVGP).

RESULTS

Both fungi showed a more pronounced degradation of lignin on a more mature straw (MS3; 89.0%) in comparison with the straw harvested at an earlier stage (MS1; 70.7%). Quantitative pyrolysis coupled to gas chromatography and mass spectrometry, using ¹³ C lignin as an internal standard ¹³ C-IS Py-GC/MS revealed that lignin in more mature straw was degraded and modified to a greater extent. In contrast, cellulose was less degraded in MS3, as compared to MS1 (8.3% versus 14.6%). There was no effect of different MS on the IVGP of the fungus-treated straws. Among the different straw cultivars, the extent of lignin degradation varied greatly (47% to 93.5%). This may explain the significant (P < 0.001) effect of cultivar on the IVGP of the fungal-treated straws. Regardless of the factors tested, both fungi were very capable of improving the IVGP of all straw types by 15.3% to 47.6%, (as compared to untreated straw), with CS performing better than LE - on different MS (33.6% versus 20.4%) and CVs (43.2% versus 29.1%).

CONCLUSION

The extent of lignin degradation caused by fungal treatment was more pronounced on the more mature and lignified straw, while variable results were obtained with different cultivars. Both fungi were capable of improving the IVGP of various straw types. © 2018 The Authors. Journal of the Science of Food and Agriculture published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Mechanistic insight in the selective delignification of wheat straw by three white-rot fungal species through quantitative 13C-IS py-GC-MS and whole cell wall HSQC NMR

BACKGROUND

The white-rot fungi Ceriporiopsis subvermispora (Cs), Pleurotus eryngii (Pe), and Lentinula edodes (Le) have been shown to be high-potential species for selective delignification of plant biomass. This delignification improves polysaccharide degradability, which currently limits the efficient lignocellulose conversion into biochemicals, biofuels, and animal feed. Since selectivity and time efficiency of fungal delignification still need optimization, detailed understanding of the underlying mechanisms at molecular level is required. The recently developed methodologies for lignin quantification and characterization now allow for the in-depth mapping of fungal modification and degradation of lignin and, thereby, enable resolving underlying mechanisms.

RESULTS

Wheat straw treated by two strains of Cs (Cs1 and Cs12), Pe (Pe3 and Pe6) and Le (Le8 and Le10) was characterized using semi-quantitative py-GC-MS during fungal growth (1, 3, and 7 weeks). The remaining lignin after 7 weeks was quantified and characterized using 13C lignin internal standard based py-GC-MS and whole cell wall HSQC NMR. Strains of the same species showed similar patterns of lignin removal and degradation. Cs and Le outperformed Pe in terms of extent and selectivity of delignification (Cs ≥ Le >> Pe). The highest lignin removal [66% (w/w); Cs1] was obtained after 7 weeks, without extensive carbohydrate degradation (factor 3 increased carbohydrate-to-lignin ratio). Furthermore, though after treatment with Cs and Le comparable amounts of lignin remained, the structure of the residual lignin vastly differed. For example, Cα-oxidized substructures accumulated in Cs treated lignin up to 24% of the total aromatic lignin, a factor two higher than in Le-treated lignin. Contrarily, ferulic acid substructures were preferentially targeted by Le (and Pe). Interestingly, Pe-spent lignin was specifically depleted of tricin (40% reduction). The overall subunit composition (H:G:S) was not affected by fungal treatment.

CONCLUSIONS

Cs and Le are both able to effectively and selectively delignify wheat straw, though the underlying mechanisms are fundamentally different. We are the first to identify that Cs degrades the major β-O-4 ether linkage in grass lignin mainly via Cβ-O-aryl cleavage, while Cα-Cβ cleavage of inter-unit linkages predominated for Le. Our research provides a new insight on how fungi degrade lignin, which contributes to further optimizing the biological upgrading of lignocellulose.