Optimizing bio-physical conditions and pre-treatment options for breaking lignin barrier of maize stover feed using white rot fungi

Cloning, expression and application of a novel laccase derived from water buffalo ruminal lignin-degrading bacteria

Water buffalo is the only mammal found to degrade lignin so far, and laccase plays an indispensable role in the degradation of lignin. In this study, multiple laccase genes were amplified based on the water buffalo rumen derived lignin-degrading bacteria Bacillus cereus and Ochrobactrum pseudintermedium. Subsequently, the corresponding recombinant plasmids were transformed into E. coli expression system BL21 (DE3) for induced expression by Isopropyl-β-D-thiogalactopyranoside (IPTG). After preliminary screening, protein purification and enzyme activity assays, Lac3833 with soluble expression and high enzyme activity was selected to test its characteristics, especially the ability of lignin degradation. The results showed that the optimum reaction temperature of Lac3833 was 40 °C for different substrates. The relative activity of Lac3833 reached the highest at pH 4.5 and pH 5.5 when the substrates were ABTS or 2,6-DMP and guaiacol, respectively. Additionally, Lac3833 could maintain high enzyme activity in different temperatures, pH and solutions containing Na+, K+, Mg2+, Ca2+ and Mn2+. Importantly, compared to negative treatment, recombinant laccase Lac3833 treatment showed that it had a significant function in degrading lignin. In conclusion, this is a pioneering study to produce recombinant laccase with lignin-degrading ability by bacteria from water buffalo rumen, which will provide new insights for the exploitation of more lignin-degrading enzymes.

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.

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.

Screening the Carbon Source Type in Solid-State Fermentation with Phanerochaete chrysosporium to Improve the Forage Value of Corn Straw and Rice Straw

Poor quality straw can be made more digestible and palatable through delignification using white rot fungi as a biological treatment in SSF. The decomposition of organic matter by white rot fungi is improved when a carbon source is added. Reducing the fermentation cycle can also help retain more nutrients in straw feed. To increase rumen digestibility and nutrient utilization, corn straw and rice straw were subjected to SSF with white rot fungi (Phanerochaete chrysosporium) for 21 days. The type of carbon source (glucose, sucrose, molasses, or soluble starch) was optimized, and the nutrient composition and in vitro fermentation parameters of the fermented straw were assessed. In the fermented corn straw and rice straw supplemented with different carbon sources, the results showed a decrease in lignin content, dry matter, cellulose, and hemicellulose loss, and an increase in crude protein content after 21 days. Total volatile fatty acid and ammonium nitrogen concentrations increased significantly (p < 0.01) during in vitro fermentation. Overall, the most enhanced nutritional values for corn straw and rice straw were observed after 14 days of SSF in the groups using molasses or glucose as a carbon source.

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.

Biovalorization of Grape Stalks as Animal Feed by Solid State Fermentation Using White-Rot Fungi

This work aimed to evaluate the potential of three fungi strains, Lentinula edodes, Pleurotus eryngii, and Pleurotus citrinopileatus, to degrade lignin and enhance the nutritive value of grape stalks (GS). The GS was inoculated with the fungi and incubated under solid-state fermentation at 28 °C and 85% relative humidity for 7, 14, 21, 28, 35, and 42 days, in an incubation chamber. The influence of the treatments was evaluated by analyzing the potential modifications in the chemical composition, in vitro organic matter digestibility (IVOMD) and enzymatic kinetics. An increase (p < 0.001) in the crude protein content was observed in the GS treated with L. edodes and P. citrinopileatus at 42 days of incubation (50 and 75%, respectively). The treatment performed with L. edodes decreased (p < 0.001) lignin content by 52%, and led to higher (p < 0.001) IVOMD values at 42 days of incubation. By contrast, P. eryngii did not affect lignin content and IVOMD. A higher activity of all enzymes was also detected for the treatment with L. edodes. Results indicated that L. edodes has a great potential to enhance the nutritive value of GS as an animal feed, due to its lignin degradation selectivity.

Ultrasonic Irradiation Enables Facile Production of Lovastatin from Sugar Cane Bagasse

This study investigated the effect of ultrasound-assisted hydrogen peroxide (H₂O₂) pretreatment on sugar cane bagasse (SCB) followed by Monascus purpureus TISTR 3003 cultivation for lovastatin production under solid-state fermentation (SSF). Optimization of the pretreatment conditions was investigated using a response surface methodology (RSM). Within the range of the selected operating conditions, the optimized values of H₂O₂ concentration, amplitude, SCB dosage, and sonication time were found to be 2.74%, 83.22 μm, 2.84% and 52.29 min, respectively. The R ² value of 0.9749 indicated that the fitted model is in good agreement with the predicted and actual lovastatin production. On the basis of the optimum conditions, the lovastatin production was 2347.10 ± 17.19 μg/g, which is 2.4 times higher than that under untreated conditions. Scanning electron microscopy (SEM) analysis explored the surface structure of the untreated SCB, which showed a compact rigid structure. In contrast, treated SCB had a rough surface structure and cracks as a result of the pretreatment.

Fermentation Dynamics and Benzylic Derivative Production in Ischnoderma resinosum Isolates

Fermentation dynamics and benzylic derivative production were evaluated in the fermentation broth of six different Ischnoderma resinosum (P. Karst) isolates over a period of 30 days to understand their potential applications in bioreactor optimization for natural flavor compound production. d-Glucose and d-fructose levels decreased from 20.4 ± 0.4 to 7.1 ± 1.4 g/L and 1.0 ± 0.1 to <0.1 g/L, respectively, in all fermentations. Isolate I₂ produced the highest concentration of ethanol (546. 4 ± 0.4 mg/L). l-Lactic acid production varied between 4.3 ± 0.6 and 3.7 ± 0.2 mg/L, whereas acetic acid concentrations decreased from 81.0 ± 3.3 to <40.0 mg/L. pH decreased from 4.9 ± 0.0 to 3.6 ± 0.4 at the end of 30 days in all fermentations. Isolate I₃ was the highest producer of benzaldehyde (BA) (12.0 ± 0.2 mg/kg) and 4-methoxybenzaldehyde (4-MBA) (239.6 ± 3.9 mg/kg), while isolate I₄ was the highest producer of 3,4-dimethoxybenzaldehyde (3,4-DMBA) (27.8 ± 0.2 mg/18 kg). Identification of isolate I₃ as a high BA and 4-MBA producer and isolate I₄ as a high 3,4-DMBA producer suggested differential benzylic derivative production among I. resinosum isolates. This study lays the foundation for future investigations evaluating additional I. resinosum isolates for benzylic derivative production as well as studies aimed at bioreactor optimization with potential commercial application.