Excellent waste biomass-degrading performance of Trichoderma asperellum T-1 during submerged fermentation

Enhanced fermentation and deconstruction of natural wheat straw by Trichoderma asperellum T-1 and its positive transcriptional response

Microorganisms harvest energy from agricultural waste by degrading its structure. By comparing with Trichoderma reesei QM6a in cellulase production, straw deconstruction and transcriptome response, Trichoderma asperellum T-1 was identified to be prioritized for the fermentation of natural straw. Cellulase activity of T-1 was 50%-102% higher than QM6a. And the degradation rate of hemicellulose and ligin in wheat straw by T-1 reached 40% and 42%. Time-driven changes in the gene expression of extracellular proteins involved in polysaccharide, xylan, and hemicellulose metabolism and hydrolysis indicated that T-1 positively responded in both solid state fermentation and submerged fermentation for lignocellulose degradation. A significantly enriched category encoding carbohydrate-binding modules is considered critical for the deconstruction of the natural structure by T-1. The findings highlight the superiority of T. asperellum T-1 in straw fermentation, base on which, the construction of efficient microbial agents is expected to enhance the utilization of biomass.

On-site enriched production of cellulase enzyme using rice straw waste and its hydrolytic performance evaluation through systematic dynamic modeling

The application of on-site produced cellulolytic enzymes in place of commercial enzymes towards hydrolytic preparations of reducing sugars using inexpensive lignocellulosic wastes is considered the most efficient strategy to accomplish a cost-effective biofuel production process. Along with improved production, intrinsic and systematic performance evaluation of the produced enzyme during the hydrolysis process through kinetic intervention remains a crucial requirement for achieving the improved performance of the process. With this motivation, the present study primarily deals with the nutritionally optimized production strategy of cellulases from rice straw (RS) waste using Trichoderma reesei (MTCC 164). The highest cellulase production was obtained 8.09 ± 0.32 g/l in batch mode at optimized combinations of 3.5% (w/v) RS inducer, 3.0% (w/v) lactose, and 1.5% (w/v) peptone. Production was further improved through pH-regulated (pH 5.5 to 6.5) fed-batch fermentations. The enzyme produced at pH 6 was considered for hydrolysis studies at 4 to 10% (w/w) solid loading due to reasonable exoglucanase, endoglucanase, and maximum β-glucosidase activity levels of 9.3 U/ml, 3.87 U/ml, and 2.65 U/ml respectively. Multi-reaction systematic kinetic modeling was implemented to evaluate enzyme performance during hydrolysis, and the values of inhibitory kinetic parameters (K_2r = 7.1 < K₁r = 18.5 < K₃r = 276.6) suggested that sequential conversion of cellulose to glucose by existing enzyme components was more dominant over direct conversion.

Pretreatment of straw using filamentous fungi improves the remediation effect of straw biochar on bivalent cadmium contaminated soil

Carbonized products of waste agricultural straws used for soil remediation can reduce impact of heavy metals on soil ecology and crop growth. Here, we demonstrated straw fermentation residues to be suitable for preparation of soil remediation agents by pyrolysis. Lignocellulose degradability of filamentous fungi during fermentation was found to significantly enhance properties of biochar for cadmium (Cd (II))-contaminated paddy soil remediation. Obtained biochars were indicated to have rich oxygen-containing groups, thus showing enhanced removal ability of Cd (II). Adsorption capacity of biochar (BaWS) prepared from wheat straw, which has been fermented by Trichoderma asperellum T-1, reached 105.9 mg g^-1, 372.8% higher than that from natural wheat straw (BWS). Fermentation of straws by Trichoderma reesei QM6a can also improve the adsorption performance of biochar, but the effect is much weaker. The content of bioavailable Cd (II) in paddy soil reduced 83.7% within 15 days after addition of 1% BaWS. Significantly, adding 1% BaWS had better effect on increasing soil pH and removing available Cd (II) , than adding 3% BWS. These results suggest that the used dosage of microbial pretreated straw biochar for the remediation of Cd (II)-contaminated paddy soil was only 1/3 of that of conventional biochar. The enhanced property of biochar was attributed to deconstruction of straws by filamentous fungi before being pyrolyzed. Thus, fermented straws were indicated more suitable for the preparation of biochar used as effective soil remediation agents.

Degradation of switchgrass by Bacillus subtilis 1AJ3 and expression of a beta-glycoside hydrolase

Increasing demand for carbon neutrality has led to the development of new techniques and modes of low carbon production. The utilization of microbiology to convert low-cost renewable resources into more valuable chemicals is particularly important. Here, we investigated the ability of a cellulolytic bacterium, Bacillus subtilis 1AJ3, in switchgrass lignocellulose degradation. After 5 days of culture with the strain under 37°C, cellulose, xylan, and acid-insoluble lignin degradation rates were 16.13, 14.24, and 13.91%, respectively. Gas chromatography-mass spectrometry (GC-MS) analysis and field emission scanning electron microscopy (FE-SEM) indicated that the lignin and surface of switchgrass were degraded after incubation with the bacterial strain. Strain 1AJ3 can grow well below 60°C, which satisfies the optimum temperature (50°C) condition of most cellulases; subsequent results emphasize that acid-heat incubation conditions increase the reducing sugar content in a wide range of cellulosic biomass degraded by B. subtilis 1AJ3. To obtain more reducing sugars, we focused on β-glycoside hydrolase, which plays an important role in last steps of cellulose degradation to oligosaccharides. A β-glycoside hydrolase (Bgl-16A) was characterized by cloning and expression in Escherichia coli BL21 and further determined to belong to glycoside hydrolase (GH) 16 family. The Bgl-16A had an enzymatic activity of 365.29 ± 10.43 U/mg, and the enzyme's mode of action was explained by molecular docking. Moreover, the critical influence on temperature (50°C) of Bgl-16A also explained the high-efficiency degradation of biomass by strain under acid-heat conditions. In terms of potential applications, both the strain and the recombinant enzyme showed that coffee grounds would be a suitable and valuable substrate. This study provides a new understanding of cellulose degradation by B. subtilis 1AJ3 that both the enzyme action mode and optimum temperature limitation by cellulases could impact the degradation. It also gave new sight to unique advantage utilization in the industrial production of green manufacturing.

Whole-Genome Sequence and Comparative Analysis of Trichoderma asperellum ND-1 Reveal Its Unique Enzymatic System for Efficient Biomass Degradation

The lignocellulosic enzymes of Trichoderma asperellum have been intensely investigated toward efficient conversion of biomass into high-value chemicals/industrial products. However, lack of genome data is a remarkable hurdle for hydrolase systems studies. The secretory enzymes of newly isolated T. asperellum ND-1 during lignocellulose degradation are currently poorly known. Herein, a high-quality genomic sequence of ND-1, obtained by both Illumina HiSeq 2000 sequencing platforms and PacBio single-molecule real-time, has an assembly size of 35.75 Mb comprising 10,541 predicted genes. Secretome analysis showed that 895 proteins were detected, with 211 proteins associated with carbohydrate-active enzymes (CAZymes) responsible for biomass hydrolysis. Additionally, T. asperellum ND-1, T. atroviride IMI 206040, and T. virens Gv-298 shared 801 orthologues that were not identified in T. reesei QM6a, indicating that ND-1 may play critical roles in biological-control. In-depth analysis suggested that, compared with QM6a, the genome of ND-1 encoded a unique enzymatic system, especially hemicellulases and chitinases. Moreover, after comparative analysis of lignocellulase activities of ND-1 and other fungi, we found that ND-1 displayed higher hemicellulases (particularly xylanases) and comparable cellulases activities. Our analysis, combined with the whole-genome sequence information, offers a platform for designing advanced T. asperellum ND-1 strains for industrial utilizations, such as bioenergy production.

Current advances on waste biomass transformation into value-added products

Ceaseless growth in human population led to high demand in everything. Currently, the world largely depends on petroleum-based "all material synthesis" scheme. On the other hand, depletion of fossil-based resources and their huge impact on environmental pollution have forced us to search for sustainable and eco-friendly alternative resources. In this context, the notion to utilize waste biomass could possibly provide environmental and economic benefits. This study was carefully designed to critically review state of the art in the transformation of waste biomass into value-added products. Even though extensive reviews on biomass utilization have been published in the past few years, the current study basically focused on new trends and prospective in this area. Here, global biomass potential, research developments and practices, novel biomass transformation approaches, and future perspectives were broadly discussed. More importantly, in addition to revising published researches, already implemented and ongoing large-scale projects on valorization of waste biomass have been assessed. Therefore, this study is believed to give crucial information on the current status and future direction of waste biomass utilization so as to accomplish the quest towards green economy.Key Points • Huge biomass potential and dramatically increase in R&D trends on waste biomass.• Selection of appropriate waste biomass valorization techniques. • Development of efficient and feasible waste biomass transformation technology. • Coproduction of low-value, high-volume and high-value, low volume products.

An endoxylanase rapidly hydrolyzes xylan into major product xylobiose via transglycosylation of xylose to xylotriose or xylotetraose

Here, we proposed an effective strategy to enhance a novel endoxylanase (Taxy11) activity and elucidated an efficient catalysis mechanism to produce xylooligosaccharides (XOSs). Codon optimization and recruitment of natural propeptide in Pichia pastoris resulted in achievement of Taxy11 activity to 1405.65 ± 51.24 U/mL. Analysis of action mode reveals that Taxy11 requires at least three xylose (xylotriose) residues for hydrolysis to yield xylobiose. Results of site-directed mutagenesis indicate that residues Glu¹¹⁹, Glu²¹⁰, and Asp⁵³ of Taxy11 are key catalytic sites, while Asp²⁰³ plays an auxiliary role. The novel mechanism whereby Taxy11 catalyzes conversion of xylan or XOSs into major product xylobiose involves transglycosylation of xylose to xylotriose or xylotetraose as substrate, to form xylotetraose or xylopentaose intermediate, respectively. Taxy11 displayed highly hydrolytic activity toward corncob xylan, producing 50.44 % of xylobiose within 0.5 h. This work provides a cost-effective and sustainable way to produce value-added biomolecules XOSs (xylobiose-enriched) from agricultural waste.

Isolation of Thermostable Lignocellulosic Bacteria From Chicken Manure Compost and a M42 Family Endocellulase Cloning From Geobacillus thermodenitrificans Y7

The composting ecosystem provides a potential resource for finding new microorganisms with the capability for cellulose degradation. In the present study, Congo red method was used for the isolating of thermostable lignocellulose-degrading bacteria from chicken manure compost. A thermophilic strain named as Geobacillus thermodenitrificans Y7 with acid-resident property was successfully isolated and employed to degrade raw switchgrass at 60°C for 5 days, which resulted in the final degradation rates of cellulose, xylan, and acid-insoluble lignin as 18.64, 12.96, and 17.21%, respectively. In addition, GC-MS analysis about aromatic degradation affirm the degradation of lignin by G. thermodenitrificans Y7. Moreover, an endocellulase gene belong to M42 family was successfully cloned from G. thermodenitrificans Y7 and expressed in Escherichia coli BL21. Recombinant enzyme Cel-9 was purified by Ni-NTA column based the His-tag, and the molecular weight determined as 40.4 kDa by SDA-PAGE. The characterization of the enzyme Cel-9 indicated that the maximum enzyme activity was realized at 50°C and pH 8.6 and, Mn2+ could greatly improve the CMCase enzyme activity of Cel-9 at 10 mM, which was followed by Fe2+ and Co2+. Besides, it also found that the β-1,3-1,4, β-1,3, β-1,4, and β-1,6 glucan linkages all could be hydrolyzed by enzyme Cel-9. Finally, during the application of enzyme Cel-9 to switchgrass, the saccharification rates achieved to 1.81 ± 0.04% and 2.65 ± 0.03% for 50 and 100% crude enzyme, respectively. All these results indicated that both the strain G. thermodenitrificans Y7 and the recombinant endocellulase Cel-9 have the potential to be applied to the biomass industry.