Construction of a fungal consortium for effective degradation of rice straw lignin and potential application in bio-pulping

Optimisation of process parameters for lignocellulosic biomass degradation by Pseudomonas sp. using response surface methodology

Globally, over 5 billion tons of crop residue are produced annually, contributing to pollution and soil degradation. That's why this study used response surface methodology to biodegrade rice straw (R.S.), wheat straw (W.S.), and cabbage waste (C.W.) from Haryana using Pseudomonas parafulva (accession number SUB14741035 27F PQ357156). Six process parameters (A: temperature 30-50 °C, B: pH 5-9, C: inoculum dose 1-9 %, D: agitation rate 100-200 rpm, E: time 24-72 h and F: substrate concentration 5-15 g) for R.S., W.S., C.W. degradation was optimised through RSM. The Pseudomonas parafulva has degradation capacity (% change) of 75, 73.40 and 72.9 % for cellulose and 71.50, 70, and 71.78 % for hemicellulose for R.S., W.S. and C.W., respectively at optimised conditions (A: temperature 35 °C, B: pH 6, C: inoculum dose 3 %, D: agitation rate 100 rpm, E: time 31 h, and F: substrate concentration 7 g) with a desirability value of 1.0. ANOVA analysis was used to evaluate the degradation efficiencies of R.S., W.S., and C.W. components, revealing a significant model with p-values below 0.0001. The study suggests incorporating bacteria in crop residue management can enhance its potential applications in bioremediation, biofuel production, soil fertility improvement, and biomass degradation.

Efficient degradation of corn straw at low temperature using a novel co-cultured consortium LHWA

Straw degradation was slow under low temperature environments. A cold-tolerant consortium LHWA was constructed by Bacillus cereus, Acinetobacter lwoffii, Penicillium griseofulvum, and Talaromyces funiculosus. The consortium and culture conditions were optimized. Under 4 °C cultivation, liquid fermentation showed a 55.52 % straw weight loss rate after 30 days with inoculum (8.4 %, w/v), peptone (0.4 %, w/v) and Fe2+ concentration (0.06 %, w/v); solid fermentation showed 58.36 % straw weight loss rate after 60 days. According to transcriptomic analysis, the mechanism of cold resistance in B. cereus is to improve the fluidity of the cell membrane, including changing the composition of fatty acids, increasing the expression of cold stress response proteins and cold shock proteins. The constructed consortium LHWA significantly improved the straw degradation efficiency under cold environments.

Enhancing environmental decontamination and sustainable production through synergistic and complementary interactions of actinobacteria and fungi

Actinobacteria and fungi are renowned for their metabolic diversity and adaptability to various environments, thus exhibiting significant potential for environmental decontamination and sustainable production. Both actinobacteria and fungi excel in producing diverse secondary metabolites and enzymes, offering valuable tools for industrial and environmental applications. Their ability to detoxify metals and degrade a wide range of organic pollutants, such as pesticides, hydrocarbons, and dyes, positions them as promising candidates for bioremediation. Recent shifts in microbiological sciences emphasize research on mixed microbial populations. Microbial interactions in mixed communities emulate natural processes and yield emergent properties such as stability, robustness, and enhanced metabolism. Co-cultures of actinobacteria and fungi harness a broader range of genes and metabolic capabilities through their distinctive interactions, opening new avenues for developing novel products and/or technologies. This review provides a critical analysis of the present status of knowledge regarding the potential of actinobacteria-fungi co-cultures with a particular focus on novel functionalities and heightened production efficiency. These consortia are promising in several fields, from environmental applications to the biosynthesis of industrially relevant metabolites and enzymes, and enhancements in agricultural production. Although challenges still exist, their potential to address complex problems has been demonstrated and deserves further investigation.

Insight into the role of antioxidant in microbial lignin degradation: Ascorbic acid as a fortifier of lignin-degrading enzymes

BACKGROUND

Microbial-driven lignin depolymerization has emerged as a promising approach for lignin degradation. However, this process is hindered by the limited activity of lignin-degrading enzymes. Antioxidants are crucial for maintaining redox homeostasis in living cells, which can impact the efficiency of enzymes. Ascorbic acid (AA) is well-known for its antioxidant properties, while Trametes versicolor is a commonly used lignin-degrading fungus capable of secreting laccase (Lac) and manganese peroxidase (MnP). Thus, AA was selected as model antioxidant and added into the culture medium of T. versicolor to examine the effect of antioxidants on the activity of lignin-degrading enzymes in the fungus.

RESULTS

The presence of AA resulted in a 4.9-fold increase in the Lac activity and a 3.9-fold increase in the MnP activity, reaching 10736 U/L and 8659 U/L, respectively. This increase in enzyme activity contributed to a higher lignin degradation rate from 17.5% to 35.2%, consistent with observed morphological changes in the lignin structure. Furthermore, the addition of AA led to a reduction in the molecular weights of lignin and an increase in the content of degradation products with lower molecular weight, indicating more thorough degradation of lignin. Proteomics analysis suggested that the enhancement in enzyme activity was more likely to attributed to the reinforcement of AA on oxidative protein folding and transportation, rather than changes in enzyme expression.

CONCLUSIONS

The addition of AA enhanced the performance of enzymes responsible for lignin degradation in terms of enzyme activity, degradation rate, lignin structural change, and product mapping. This study offers a feasible strategy for enhancing the activity of lignin-degrading enzymes in the fungus and provides insights into the role of antioxidant in microbial lignin degradation.

Metabolic pathway analysis of methane from methanol as substrate in microbial consortium

Simplified anaerobic digestion (SAD) of substrates facilitates microbial methanogenic pathways. In this study, a methane-producing microbial consortium from cow dung was enriched to determine the metabolism and metabolic pathway in the SAD of methanol. The results showed that methanol as a sole substrate produced 167 mL of methane at 10 days significantly higher than 58 mL, 17.6 mL, and 4 mL generated when methanol was combined with sodium formate, sodium formate alone, or sodium acetate. The relative abundance of Methanobacterium, Candidatus_Methanomethylophilus, Methanomassiliicoccus, and Methanosarcina was increased by 5.96 %, 3.77 %, 2.85 %, and 0.14 % in the methanol substrate of AD, respectively. Macrogenome sequencing indicates that methanol wasconverted into Methyl-CoM in the presence of Methanosarcina, which combines with Coenzyme B to produce methane. This study revealed that methanol is converted into methane by a simple pathway.

Synergistic analysis of lignin degrading bacterial consortium and its application in rice straw fiber film

Fiber film have received widespread attention due to its green friendliness. We can use microorganisms to degrade lignin in straw to obtain cellulose and make fiber films. Herein, a group of high-temperature (50 °C) lignin degrading bacterial consortium (LDH) was enriched and culture conditions for lignin degradation were optimized. Combined with high-throughput sequencing technology, the synergistic effect of LDH-composited bacteria was analyzed. Then LDH was used to treat rice straw for the bio-pulping experiment. The results showed that the lignin of rice straw was degraded 32.4 % by LDH at 50 °C for 10 d, and after the optimization of culture conditions, lignin degradation rate increased by 9.05 % (P < 0.001). The bacteria that compose in LDH can synergistically degrade lignin. Paenibacillus can encode all lignin-degrading enzymes present in the LDH. Preliminary tests of LDH in the pulping industry have been completed. This study is the first to use high temperature lignin degrading bacteria to fabricate fiber film.

From waste to protein: a new strategy of converting composted distilled grain wastes into animal feed

Distilled grain waste (DGW) is rich in nutrients and can be a potential resource as animal feed. However, DGW contains as much as 14% lignin, dramatically reducing the feeding value. White-rot fungi such as Pleurotus ostreatus could preferentially degrade lignin with high efficiency. However, lignin derivatives generated during alcohol distillation inhibit P. ostreatus growth. Thus, finding a new strategy to adjust the DGW properties to facilitate P. ostreatus growth is critical for animal feed preparation and DGW recycling. In this study, three dominant indigenous bacteria, including Sphingobacterium thermophilum X1, Pseudoxanthomonas byssovorax X3, and Bacillus velezensis 15F were chosen to generate single and compound microbial inoculums for DGW composting to prepare substrates for P. ostreatus growth. Compared with non-inoculated control or single microbial inoculation, all composite inoculations, especially the three-microbial compound, led to faster organic metabolism, shorter composting process, and improved physicochemical properties of DGW. P. ostreatus growth assays showed the fastest mycelial colonization (20.43 μg·g-1 ergosterol) and extension (9 mm/d), the highest ligninolytic enzyme activities (Lac, 152.68 U·g-1; Lip, 15.56 U·g-1; MnP, 0.34 U·g-1; Xylanase, 10.98 U·g-1; FPase, 0.71 U·g-1), and the highest lignin degradation ratio (30.77%) in the DGW sample after 12 h of composting with the three-microbial compound inoculation when compared to other groups. This sample was relatively abundant in bacteria playing critical roles in amino acid, carbohydrate, energy metabolism, and xenobiotic biodegradation, as suggested by metagenomic analysis. The feed value analysis revealed that P. ostreatus mycelia full colonization in composted DGW led to high fiber content retention and decreased lignin content (final ratio of 5% lignin) but elevated protein concentrations (about 130 g·kg-1 DM). An additional daily weight gain of 0.4 kg/d was shown in cattle feeding experiments by replacing 60% of regular feed with it. These findings demonstrate that compound inoculant consisting of three indigenous microorganisms is efficient to compost DGW and facilitate P. ostreatus growth. P. ostreatus decreased the lignin content of composted DGW during its mycelial growth, improving the quality of DGW for feeding cattle.

Development of bio-mechanical rice straw pulp by high consistency kneader with thermal and Alkaline

The purpose of this study was to develop a bio-mechanical pulp from rice straw with thermal and low chemical dosage. The process is carried out by thermal alkali kneading pretreatment (0-5% NaOH) with a high concentration kneader, enzyme pretreatment (0.2-4%) and Hollander beater. The results showed that the addition of NaOH was the main factor affecting the properties of pulp and paper, and the best properties of straw pulp could be obtained when NaOH and enzyme dosage were 5% and 0.2%, respectively. Although the optimum rice straw pulp is inferior to straw soda pulp in terms of tensile, burst and ring crush index, it is superior to old corrugated cardboard pulp and partially meets the CNS standards of corrugated medium paper and linerboard without the addition of chemicals. Therefore, the bio-mechanical rice straw pulp in this study has the potential to be produced as industrial paper.

Laccase-Based Self-Amplifying Catalytic System Enables Efficient Antibiotic Degradation for Sustainable Environmental Remediation

Antibiotic contamination poses potential risks to ecosystems and human health. Laccase (LAC) has emerged as a promising biocatalyst for the oxidation of environmentally toxic contaminants with high catalytic efficiency; however, its large-scale application is hindered by enzyme costs and dependency on redox mediators. Herein, a novel self-amplifying catalytic system (SACS) for antibiotic remediation that does not require external mediators is developed. In SACS, a natural mediator-regenerating koji with high-activity LAC, derived from lignocellulosic waste, initiates the chlortetracycline (CTC) degradation. Subsequently, an intermediate product, CTC327, identified as an active mediator for LAC via molecular docking, is formed and then starts a renewable reaction cycle, including CTC327-LAC interaction, stimulated CTC bioconversion, and self-amplifying CTC327 release, thus enabling highly efficient antibiotic bioremediation. In addition, SACS exhibits excellent performance in producing lignocellulose-degrading enzymes, highlighting its potential for lignocellulosic biomass deconstruction. To demonstrate its effectiveness and accessibility in the natural environment, SACS is used to catalyze in situ soil bioremediation and straw degradation. The resulting CTC degradation rate is 93.43%, with a straw mass loss of up to 58.35% in a coupled process. This mediator regeneration and waste-to-resource conversion in SACS provides a promising route for environmental remediation and sustainable agricultural practices.

Additive facilitated co-composting of lignocellulosic biomass waste, approach towards minimizing greenhouse gas emissions: An up to date review

Although the composting of lignocellulosic biomass is an emerging waste-to-wealth approach towards organic waste management and circular economy, it still has some environmental loopholes that must be addressed to make it more sustainable and reliable. The significant difficulties encountered when composting lignocellulosic waste biomass are consequently discussed in this study, as well as the advances in science that have been achieved throughout time to handle these problems in a sustainable manner. It discusses an important global concern, the emission of greenhouse gases during the composting process which limits its applicability on a broader scale. Furthermore, it discusses in detail, how different organic minerals and biological additives modify the physiochemical and biological characteristics of compost, aiming at developing eco-friendly compost with minimum odor, greenhouse gases emission and an optimum C/N ratio. It brings novel insights by demonstrating the effect of additives on the microbial enzymes and their pathways involved in the degradation of lignocellulosic biomass. This review also highlights the limitations of the application of additives in composting and suggests possible ways to overcome these limitations in the future for the sustainable and eco-friendly management of agricultural waste. The present review concludes that the use of additives in the co-composting of lignocellulosic biomass can be a viable remedy for the ongoing issues with the management of lignocellulosic waste.

Challenges in developing strategies for the valorization of lignin-a major pollutant of the paper mill industry

Apart from protecting the environment from undesired waste impacts, wastewater treatment is a crucial platform for recovery. The exploitation of suitable technology to transform the wastes from pulp and paper industries (PPI) to value-added products is vital from an environmental and socio-economic point of view that will impact everyday life. As the volume and complexity of wastewater increase in a rapidly urbanizing world, the challenge of maintaining efficient wastewater treatment in a cost-effective and environmentally friendly manner must be met. In addition to producing treated water, the wastewater treatment plant (WWTP) has a large amount of paper mill sludge (PMS) daily. Sludge management and disposal are significant problems associated with wastewater treatment plants. Applying the biorefinery concept is necessary for PPI from an environmental point of view and because of the piles of valuables contained therein in the form of waste. This will provide a renewable source for producing valuables and bio-energy and aid in making the overall process more economical and environmentally sustainable. Therefore, it is compulsory to continue inquiry on different applications of wastes, with proper justification of the environmental and economic factors. This review discusses current trends and challenges in wastewater management and the bio-valorization of paper mills. Lignin has been highlighted as a critical component for generating valuables, and its recovery prospects from solid and liquid PPI waste have been suggested.

Designed High-Redox Potential Laccases Exhibit High Functional Diversity

White-rot fungi secrete an impressive repertoire of high-redox potential laccases (HRPLs) and peroxidases for efficient oxidation and utilization of lignin. Laccases are attractive enzymes for the chemical industry due to their broad substrate range and low environmental impact. Since expression of functional recombinant HRPLs is challenging, however, iterative-directed evolution protocols have been applied to improve their expression, activity, and stability. We implement a rational, stabilize-and-diversify strategy to two HRPLs that we could not functionally express. First, we use the PROSS stability-design algorithm to allow functional expression in yeast. Second, we use the stabilized enzymes as starting points for FuncLib active-site design to improve their activity and substrate diversity. Four of the FuncLib-designed HRPLs and their PROSS progenitor exhibit substantial diversity in reactivity profiles against high-redox potential substrates, including lignin monomers. Combinations of 3-4 subtle mutations that change the polarity, solvation, and sterics of the substrate-oxidation site result in orders of magnitude changes in reactivity profiles. These stable and versatile HRPLs are a step toward generating an effective lignin-degrading consortium of enzymes that can be secreted from yeast. The stabilize-and-diversify strategy can be applied to other challenging enzyme families to study and expand the utility of natural enzymes.

Integrated biorefinery approaches for the industrialization of cellulosic ethanol fuel

Lignocellulosic biomass is an abundant and sustainable raw material, but its conversion into ethanol fuel has not yet achieved large-scale industrialization and economic benefits. Integrated biorefineries have been widely identified as the key to achieving this goal. Here, four promising routes were summarized to assemble the new industrial plants for cellulose-based fuels and chemicals, including 1) integration of cellulase production systems into current cellulosic ethanol processes; 2) combination of processes and facilities between cellulosic ethanol and first-generation ethanol; 3) application of enzyme-free saccharification processes and computational approaches to increase the bioethanol yield and optimize the integration process; 4) production of multiple products to maximize the value derived from the lignocellulosic biomass. Finally, the remaining challenges and perspectives of this field are also discussed.

Fermenting and Lignin Degradability of a White-Rot Fungus Coriolopsis trogii Using Industrial Lignin as Substrate

Bio-depolymerized the lignin macromolecules into low molecular lignin-derived aromatic compounds satisfies the requirement for carbon dioxide peaking and is also one of the important ways to realize lignin valorization. Coriolopsis trogii is a kind of less reported lignin-degrading white-rot fungus. The degradability of a self-isolated C. trogii TS01 on industrial lignins, including enzymatic hydrolysis lignin (EHL) and Kraft lignin (KL), was investigated in this paper. The results indicated that EHL could be used as an efficient carbon source to promote the cell growth and ligninolytic enzyme secretion of C. trogii TS01. Compared with using 2% glucose as carbon source, 1% EHL plus 1% glucose would increase the maximum cell dry weight, laccase activity, and manganese-dependent peroxidase activity of C. trogii TS01 by 24.8%, 164.1%, and 200%, respectively. However, the cell growth and ligninolytic enzyme secretion would be significantly inhibited in the case of 1% KL plus 1% glucose used as carbon source. As a result, at the 12th day of fermentation, the degradation rates of EHL and KL were 50.6% and 5.7%, respectively. The UV and FTIR analysis indicated that after been fermented by C. trogii TS01, S-unit content in EHL was decreased by 12.5% but G-unit content was increased by 53.7%. In conclusion, the research of this paper will provide a promising solution for the valorization of enzymatic hydrolysis lignin since the high biodegradation rate of lignin and high activity of ligninolytic enzymes could be achieved simultaneously.

Stable and Functionally Diverse Versatile Peroxidases Designed Directly from Sequences

White-rot fungi secrete a repertoire of high-redox potential oxidoreductases to efficiently decompose lignin. Of these enzymes, versatile peroxidases (VPs) are the most promiscuous biocatalysts. VPs are attractive enzymes for research and industrial use but their recombinant production is extremely challenging. To date, only a single VP has been structurally characterized and optimized for recombinant functional expression, stability, and activity. Computational enzyme optimization methods can be applied to many enzymes in parallel but they require accurate structures. Here, we demonstrate that model structures computed by deep-learning-based ab initio structure prediction methods are reliable starting points for one-shot PROSS stability-design calculations. Four designed VPs encoding as many as 43 mutations relative to the wildtype enzymes are functionally expressed in yeast, whereas their wildtype parents are not. Three of these designs exhibit substantial and useful diversity in their reactivity profiles and tolerance to environmental conditions. The reliability of the new generation of structure predictors and design methods increases the scale and scope of computational enzyme optimization, enabling efficient discovery and exploitation of the functional diversity in natural enzyme families directly from genomic databases.

Lignin valorization: Status, challenges and opportunities

As an abundant aromatic biopolymer, lignin has the potential to produce various chemicals, biofuels of interest through biorefinery activities and is expected to benefit the future circular economy. However, lignin valorization is hindered by a series of constraints such as heterogeneous polymeric nature, intrinsic recalcitrance, strong smell, dark colour, challenges in lignocelluloses fractionation and the presence of high bond dissociation enthalpies in its functional groups etc. Nowadays, industrial lignin is mostly combusted for electricity production and the recycling of inorganic compounds involved in the pulping process. Given the research and development on lignin valorization in recent years, important applications such as lignin-based hydrogels, surfactants, three-dimensional printing materials, electrodes and production of fine chemicals have been systematically reviewed. Finally, this review highlights the main constraints affecting industrial lignin valorization, possible solutions and future perspectives, in the light of its abundance and its potential applications reported in the scientific literature.