Lignin depolymerization and utilization by bacteria

Comparative analysis of different Phyllostachys species on gut microbiome and fecal metabolome in giant pandas (Ailuropoda melanoleuca)

The influences of different bamboo species on the microbiome and metabolome of giant pandas (Ailuropoda melanoleuca) remain understudied. The aim of this study was to investigate the effects of different Phyllostachys species on the gut microbial communities and fecal metabolite profiles in giant pandas. Metagenome and metabolome were performed on the feces of giant pandas fed with different Phyllostachys species (P. edulis, P. iridescens, P. glauca, and P. violascens). The results of metagenome showed that dietary with P. glauca could notably decrease the microbial Shannon index. The relative abundances of both Cellulosilyticum and Pseudomonas were enhanced after dietary with P. iridescens, suggesting P. iridescens could enhance the cellulose-degrading function in giant pandas. However, dietary with P. glauca or P. violascens could increase the relative abundances of certain pathogenic bacteria (Escherichia, Shigella, and Klebsiella). Metabolomics analysis further revealed that all experimental groups exhibited notably elevated levels of fecal flavonoids and fatty acids. In addition, the correlation analysis showed that certain nutrients of bamboo leaves (mainly crude protein and Cu) were significantly correlated with several differential gut bacteria and fecal metabolites. Based on the present results, P. iridescens might be a substitute for the routinely used Phyllostachys species (P. edulis) in the captive management of giant pandas. The results have revealed that bamboo species is an important factor affecting the gut microbiota and fecal metabolites in giant pandas. Our results could provide important information about bamboo species-induced alterations on the microbiome and metabolome in giant pandas.

Emerging biotechnological strategies advancing biological lignin valorization towards polyhydroxyalkanoates

Lignin is the largest renewable aromatic resource available for producing high-value products such as biomaterials, biofuels, and chemicals. Polyhydroxyalkanoate (PHA) is a biodegradable and biocompatible polymer synthesized by various microorganisms, offering broad application potential. Microbial conversion of lignin-derived aromatics into PHA promoted both lignin valorization and PHA biosynthesis. However, lignin's recalcitrance and heterogeneity pose significant challenges for its microbial degradation and value-added utilization. This review examines the entire pathway of lignin conversion into high-value products, highlighting the advantages of microbial processes for synthesizing PHA and promoting the biological upgrading of lignin. Additionally, synthetic biology techniques and metabolic regulation strategies can further enhance microbial PHA synthesis. Overall, integrating microbial PHA synthesis with lignin bioconversion not only facilitates lignin valorization but also supports the sustainable production of PHA, making a significant contribution to the utilization and sustainable development of biomass resources.

Microbial Upgrading of Lignin Depolymerization: Enhancing Efficiency with Lignin-First Catalysis

Chemical depolymerization of lignin is a non-selective process that often generates a wide distribution of product compounds, denoted herein as lignin breakdown products (LBPs). To address this limitation, we developed a hybrid lignin conversion process that employs a lignin-first catalytic approach on biomass and subsequent microbial upgrading. A Pd/C catalyst was used for reductive catalytic fractionation (RCF) of poplar biomass, and Rhodococcus opacus PD630 (R. opacus PD630) was then cultivated on the resulting LBPs. This RCF approach increases the total biomass utilization by R. opacus PD630 over base-catalyzed depolymerization (BCD) reactions that were performed in the absence of Pd/C and molecular hydrogen (H2). LBPs generated using RCF resulted in higher cell growth per gram of biomass. Cellulose in the residual biomass after RCF treatment also showed enhanced enzymatic digestibility due to saccharification yields over 40%. Techno-economic analysis (TEA) and life cycle analysis (LCA) of this hybrid lignin conversion scheme, integrated into a cellulosic bioethanol plant, decreased the minimum ethanol selling price from $4.07/gallon (base case) to $3.94/gallon. Global warming potentials ranged from 29 and 30.5 CO2,eq/MJ. These results highlight the potential for an industrial hybrid conversion-based biorefinery scheme that utilizes lignin-first catalytic deconstruction and R. opacus PD630 upgrading.

Evaluation of Acidic Deep Eutectic Solvents Treatment on Enzymatic Hydrolysis Lignins: Structural Analysis and Antioxidant Activity

The high-value utilization of enzymatic hydrolysis lignin (EHL) is essential for promoting the development of the biorefinery industry. This study investigated the enhancement of the antioxidant activity and ultraviolet (UV) absorption capacity of EHL through treatment with choline chloride (ChCl)-based acidic deep eutectic solvents (DESs). The yield, chemical structure, UV absorption properties, antioxidant activity, and thermal stability of the degraded and regenerated enzymatic hydrolysis lignin (DEHL) were analyzed. The results indicated that treatment with DESs effectively preserved the aromatic structure of EHL. Compared to untreated EHL, DEHL exhibited an increased O/C atomic ratio, a decreased UV transmittance, a significant reduction in weight-average molecular weight (Mw), and a notable increase in phenolic hydroxyl (ArOH) content. Notably, DEHL treated with ChCl-p-toluenesulfonic acid had the lowest Mw (1586 g/mol) and the highest ArOH content. Except for the ChCl-malic acid and ChCl-acetic acid systems, all the other five DES treatments enhanced the antioxidant activity of DEHL to varying degrees. Among them, DEHL treated with ChCl-p-toluenesulfonic acid exhibited the highest antioxidant activity, with an IC50 DPPH value of 262.87 μg/mL.

Increased temperature enhances microbial-mediated lignin decomposition in river sediment

BACKGROUND

Lignin, as the most abundant recalcitrant organic carbon in terrestrial ecosystems, plays a crucial role in the Earth's carbon cycle. After lignin entering aquatic environments, portion of it tends to accumulate in sediments, forming a stable carbon relatively reservoir. However, the increasing temperature caused by human activities may impact microbial-mediated lignin decomposition, thereby affecting sedimentary carbon reservoirs. Therefore, revealing how temperature affects microbial-mediated lignin decomposition in river sediment, a topic that remains elusive, is essential for comprehending the feedbacks between river carbon reservoirs and climate. To address this, we conducted stable isotope probing of river surface sediment using 13C-lignin and 13C-vanillin, and utilized a series of techniques, including CO2 production analysis, 16S rRNA gene amplicon sequencing, metagenomics, and metatranscriptomics, to identify the lignin-decomposing microbes and the effects of temperature on microbial-mediated lignin decomposition.

RESULTS

We found that elevated temperatures not only increased the total sediment respiration (total CO2) and the CO2 emissions from lignin/vanillin decomposition, but also enhanced priming effects. The 13C-labled taxa, including Burkholderiales, Sphingomonadales, and Pseudomonadales, were identified as the main potential lignin/vanillin decomposers, and their abundances and activity significantly increased as temperature increased. Furthermore, we observed that increasing temperature significantly increased the activity of lignin decomposing pathways, including β-aryl ether fragments and 4,5-PDOG pathway. Additionally, as temperature increases, the transcriptional abundances of other carbon cycling related genes, such as pulA (starch decomposition) and xyla (hemicellulose decomposition), also exhibited increasing trends. Overall, our study elucidated the potential lignin-decomposing microbes and pathways in river sediment and their responses to temperature increasing.

CONCLUSIONS

Our study demonstrated that the temperature increasing can increase the rate of lignin/vanillin decomposition via affecting the activity of lignin-decomposing microbes. This finding indicates that the ongoing intensification of global warming may enhance the decomposition of recalcitrant organic carbon in river sediment, thereby impacting global carbon cycling. Video Abstract.

Quantitative Analysis of Coupled Carbon and Energy Metabolism for Lignin Carbon Utilization in Pseudomonas putida

Soil Pseudomonas species, which can thrive on lignin-derived phenolic compounds, are widely explored for biotechnology applications. Yet, there is limited understanding of how the native metabolism coordinates phenolic carbon processing with cofactor generation. Here, we achieve quantitative understanding of this metabolic balance through a multi-omics investigation of Pseudomonas putida KT2440 grown on four common phenolic substrates: ferulate, p-coumarate, vanillate, and 4-hydroxybenzoate. Relative to succinate as a non-aromatic reference, proteomics data reveal >140-fold increase in proteins for transport and initial catabolism of each phenolic substrate, but metabolomics profiling reveals that bottleneck nodes in initial phenolic compound catabolism maintain more favorable cellular energy state. Up to 30-fold increase in pyruvate carboxylase and glyoxylate shunt proteins implies a metabolic remodeling confirmed by kinetic 13C-metabolomics. Quantitative analysis by 13C-fluxomics demonstrates coupling of this remodeling with cofactor production. Specifically, anaplerotic carbon recycling via pyruvate carboxylase promotes fluxes in the tricarboxylic acid cycle to provide 50-60% NADPH yield and 60-80% NADH yield, resulting in 2-fold higher ATP yield than for succinate metabolism; the glyoxylate shunt sustains cataplerotic flux through malic enzyme for the remaining NADPH yield. The quantitative blueprint elucidated here explains deficient versus sufficient cofactor rebalancing during manipulations of key metabolic nodes in lignin valorization.

Solvent-Free Catalytic Hydrotreatment of Lignin to Biobased Aromatics: Current Trends, Industrial Approach, and Future Perspectives

Lignin is the only naturally occurring, renewable biopolymer and an alternative for the production of six-membered aromatic chemicals. The utilization of lignin can increase the additional revenue of biorefineries and reduce the dependence on crude oil for the production of aromatic chemicals. Therefore, the development of technologies for the production of valuable chemicals from lignin waste in biorefineries is of great importance. Catalytic hydrotreatment of lignin is considered one of the most promising technologies for the production of biobased aromatic chemicals and fuels. Among the various hydrotreatment routes, the solvent-free hydrotreatment approach is advantageous because this process reduces production costs and is similar to petroleum refinery processes such as cracking and heteroatom removal. This review addresses recent developments in solvent-free catalytic hydrotreatment of various lignins such as sulfur-containing, sulfur-free, and pyrolytic lignins to produce low oxygen-containing aromatics such as alkylphenolics in batch, semicontinuous, and continuous reactors. Special emphasis is given to the various noble and non-noble metal catalysts, the best route between single and two-stage processing, key factors in solvent-free depolymerization of lignin, techno-economic evaluation, crude oil vs lignin oil refining, challenges and future prospects, etc.

The microbiota of cork and yellow stain as a model for a new route for the synthesis of chlorophenols and chloroanisoles from the microbial degradation of suberin and/or lignin

BACKGROUND

The main application of cork is the production of stoppers for wine bottles. Cork sometimes contains 2,4,6-trichloroanisole, a compound that, at a concentration of ng/L, produces an unpleasant musty odor that destroys the organoleptic properties of wine and results in enormous economic losses for wineries and cork industries. Cork can exhibit a defect known as yellow stain, which is associated with high levels of 2,4,6-trichloroanisole. We describe how the microbiota of cork and yellow stain define a novel mechanism that explains the formation of chlorophenols and chloroanisoles (including 2,4,6-trichloroanisole) from p-hydroxybenzoate produced during lignin and/or suberin breakdown.

RESULTS

Electron microscopy revealed that cork affected by yellow stain exhibited significant structural degradation. This deterioration was attributed to the presence of higher microbial populations compared to those found in standard cork. Cork microbiota is rich in filamentous fungi able to metabolize lignin. A metataxonomic analysis confirmed that yellow stain contained significantly greater populations of fungal species belonging to Absidia, Geomyces, Mortierella, Mucor, Penicillium, Pseudogymnoascus, Talaromyces, and Umbelopsis. It also contained significantly greater amounts of bacteria belonging to Enterobacterales, Streptosporangiales, Tepidisphaerales, Pseudomonas, and several members of Burkholderiaceae, particularly species of the Burkholderia-Caballeronia-Paraburkholderia group. The extraction of aromatic compounds from cork samples allowed the identification of several compounds typically observed following lignin depolymerization. Notably, p-hydroxybenzoic acid and phenol were detected. Two strains of the genus Streptomyces isolated from yellow stain were able to biotransform p-hydroxybenzoate into phenol in resting cell assays. Phenol could be efficiently chlorinated in vitro to produce 2,4,6-trichlorophenol by a fungal chloroperoxidase, an enzymatic activity commonly found in filamentous fungi isolated from cork. Finally, as has been widely demonstrated before, 2,4,6-trichlorophenol can be efficiently O-methylated to 2,4,6-trichloroanisole by many of fungi that inhabit cork.

CONCLUSIONS

Chlorophenols and chloroanisoles can be produced de novo in cork from p-hydroxybenzoate generated by the microbial biodegradation of lignin and/or suberin through the participation of different types of microorganisms present in cork. The natural origin of these compounds, which are of great interest for the chlorine cycle and represent a new source of environmental contamination that differs from that caused by human activity, is described. Video Abstract.

Lignin extraction from lignocellulosic biomass and its valorization to therapeutic phenolic compounds

Lignocellulosic biomass is a sustainable alternative to finite petroleum resources, with lignin emerging as a major component of biomass for producing circular economy products. Maximizing extraction and valorization of lignin to platform chemicals, biofuels, and bioactive compounds is crucial. Unlocking lignin's full potential lies in exploring the therapeutic properties of lignin-derived phenolics, which can definitely boost the economic viability of integrated biorefineries. This review provides a broad vision of lignin valorization stages, covering various techniques of its extraction from lignocellulosic biomass with high yield and purity and its further depolymerization to phenolics. Therapeutic potential of lignin-derived phenols as antioxidants, antimicrobials, anti-inflammatory, and anticancer agents is comprehensively discussed. Lignin, with high phenolic hydroxyl content up to 97% purity, can be extracted using deep eutectic solvents (DES) and organosolv processes. Oxidative and reductive catalytic depolymerization methods efficiently break down lignin into valuable phenolic compounds like alkyl phenolics and vanillin, even at mild temperatures, making them a preferred choice for lignin valorization. Potential of lignin derived phenolics as versatile bioactive compounds with health promoting benefits is highlighted. Phenolics such as vanillin, ferulic acid, and syringic acid have demonstrated the ability to modulate cellular pathways involved in the pathogenesis of diseases like cancer and diabetes. The interplay between high purity lignin extraction and therapeutic potential of lignin-derived phenolics unveils a new frontier in sustainable healthcare solutions.

Bacterial valorization of lignin for the sustainable production of value-added bioproducts

As the most abundant aromatic biopolymer in the biosphere, lignin represents a promising alternative feedstock for the industrial production of various value-added bioproducts with enhanced economical value. However, the large-scale implementation of lignin valorization remains challenging because of the heterogeneity and irregular structure of lignin. General fragmentation and depolymerization processes often yield various products, but these approaches necessitate tedious purification steps to isolate target products. Moreover, microbial biocatalytic processes, especially bacterial-based systems with high metabolic activity, can depolymerize and further utilize lignin in an eco-friendly way. Considering that wild bacterial strains have evolved several metabolic pathways and enzymatic systems for lignin degradation, substantial efforts have been made to exploit their potential for lignin valorization. This review summarizes recent advances in lignin valorization for the production of value-added bioproducts based on bacterial systems. Additionally, the remaining challenges and available strategies for lignin biodegradation processes and future trends of bacterial lignin valorization are discussed.

Mini-review on lignin-based self-healing polymer

Lignin, a biopolymer derived from plant biomass, is recognized as a highly promising substance for developing self-healing polymers owing to its dynamic linkages and functional groups. This paper provides a thorough review of lignin-based self-healing polymer, from the process of extracting lignin, chemical modification, synthesis techniques such as via reversible addition-fragmentation chain transfer (RAFT) polymerization, crosslinking with polymers like polyvinyl alcohol (PVA) and chitosan, and reactions with isocyanates to create lignin-based networks with reversible interactions. This work also summarizes the optimization of self-healing ability, such as including dynamic copolymers, encapsulating healing agents like dicyclopentadiene and polycaprolactone (PCL), and chain extenders with disulfide or Diels-Alder (DA) moieties. The material's characterization focuses on its capacity to recover via hydrogen bonding and dynamic re-associations, improved mechanical properties from lignin's rigid structure, and enhanced temperature resistance. Primary obstacles involve the optimization of lignin extraction, enhancement of polymer compatibility, and the establishment of efficient procedures for synthesis and characterization. Overall, lignin shows great potential as a renewable component of self-healing polymers, with plenty of opportunities for further development.

Analysis of novel bacterial metagenome-assembled genomes from lignin-degrading microbial consortia

Despite recent progress, bacterial degradation of lignin is not completely understood. To address the mechanisms that bacteria from unknown taxonomic groups use to perform lignin-monomer degradation, functional analysis of bacterial metagenome-assembled genomes from soil-derived consortia enriched for microorganisms capable of degrading lignin was performed. A total of 232 metagenome-assembled genomes were recovered. After applying quality criteria of at least 70 % genome completeness and contamination less than or equal to 10 %, 39 genomes were obtained. From these, a total of 14 genomes from bacteria of unknown classification at lower taxonomic levels (i.e., only classified to the order level or higher) were chosen for further functional analysis. A global analysis of the potential ecological functions of these bacteria was performed, followed by a detailed analysis of monolignol degradation pathways. The phylum with the highest number of genomes was Proteobacteria. The genomes presented functions consistent with soil-derived bacteria, like denitrification, with different metabolic capacities related to the sulfur, chlorine, arsenic and carbon cycles, in addition to the degradation of plant cell wall components like cellulose, hemicellulose, and lignin. The Sphingomonadales_OP 08 genome showed the greatest potential to degrade cellulose and hemicellulose, although it does not appear to be able to degrade lignin. The Actinobacteria_BY 70 genome presented the highest number of enzymes and pathways related to the degradation of monolignols; furthermore, it showed the greatest potential for aromatic ring breakage by different fission pathways. The genomes of the two Actinobacteria showed the caffeic acid pathway, an important phenolic compound presenting several biological properties, such as antimicrobial and antioxidant. To our knowledge, this is the first time this pathway has been reported in this class of bacteria.

Enterobacter spp. isolates from an underground coal mine reveal ligninolytic activity

Lignin, the second most abundant renewable carbon source on earth, holds significant potential for producing biobased specialty chemicals. However, its complex, highly branched structure, consisting of phenylpropanoic units and strong carbon-carbon and ether bonds, makes it highly resistant to depolymerisation. This recalcitrancy highlights the need to search for robust lignin-degrading microorganisms with potential for use as industrial strains. Bioprospecting for microorganisms from lignin-rich niches is an attractive approach among others. Here, we explored the ligninolytic potential of bacteria isolated from a lignin-rich underground coalmine, the Morupule Coal Mine, in Botswana. Using a culture-dependent approach, we screened for the presence of bacteria that could grow on 2.5% kraft lignin-supplemented media and identified them using 16 S rRNA sequencing. The potential ligninolytic isolates were evaluated for their ability to tolerate industry-associated stressors. We report the isolation of twelve isolates with ligninolytic abilities. Of these, 25% (3) isolates exhibited varying robust ligninolytic ability and tolerance to various industrial stressors. The molecular identification revealed that the isolates belonged to the Enterobacter genus. Two of three isolates had a 16 S rRNA sequence lower than the identity threshold indicating potentially novel species pending further taxonomic review. ATR-FTIR analysis revealed the ligninolytic properties of the isolates by demonstrating structural alterations in lignin, indicating potential KL degradation, while Py-GC/MS identified the resulting biochemicals. These isolates produced chemicals of diverse functional groups and monomers as revealed by both methods. The use of coalmine-associated ligninolytic bacteria in biorefineries has potential.

Perspective on Lignin Conversion Strategies That Enable Next Generation Biorefineries

The valorization of lignin, a currently underutilized component of lignocellulosic biomass, has attracted attention to promote a stable and circular bioeconomy. Successful approaches including thermochemical, biological, and catalytic lignin depolymerization have been demonstrated, enabling opportunities for lignino-refineries and lignocellulosic biorefineries. Although significant progress in lignin valorization has been made, this review describes unexplored opportunities in chemical and biological routes for lignin depolymerization and thereby contributes to economically and environmentally sustainable lignin-utilizing biorefineries. This review also highlights the integration of chemical and biological lignin depolymerization and identifies research gaps while also recommending future directions for scaling processes to establish a lignino-chemical industry.

Extracellular ligninases production and lignin degradation by Paenibacillus polymyxa

Bacteria represent an attractive source for the isolation and identification of potentially useful microorganisms for lignin depolymerization, a process required for the use of agricultural waste. In this work, ten autochthonous bacteria isolated from straw, cow manure, and composts were characterized for potential use in the biodelignification of the waste. A comparison of the ability to degrade lignin and the efficiency of ligninolytic enzymes was performed in bacteria grown in media with lignin as a sole carbon source (LLM, 3.5g/L lignin-alkali) and in complex media supplemented with All-Ban fiber (FLM, 1.5g/L). Bacterial isolates showed different abilities to degrade lignin, they decreased the lignin concentration from 7.6 to 18.6% in LLM and from 11.1 to 44.8% in FLM. They also presented the activity of manganese peroxidase, lignin peroxidases, and laccases with different specific activities. However, strain 26 identified as Paenibacillus polymyxa by sequencing the 16S rRNA showed the highest activity of lignin peroxidase and the ability to degrade efficiently lignocellulose. In addition, P. polymyxa showed the highest potential (desirability ≥ 0.795) related to the best combination of properties to depolymerize lignin from biomass. The results suggest that P. polymyxa has a coordinated lignin degradation system constituted of lignin peroxidase, manganese peroxidase, and laccase enzymes.

Engineered acetogenic bacteria as microbial cell factory for diversified biochemicals

Acetogenic bacteria (acetogens) are a class of microorganisms with conserved Wood-Ljungdahl pathway that can utilize CO and CO2/H2 as carbon source for autotrophic growth and convert these substrates to acetate and ethanol. Acetogens have great potential for the sustainable production of biofuels and bulk biochemicals using C1 gases (CO and CO2) from industrial syngas and waste gases, which play an important role in achieving carbon neutrality. In recent years, with the development and improvement of gene editing methods, the metabolic engineering of acetogens is making rapid progress. With introduction of heterogeneous metabolic pathways, acetogens can improve the production capacity of native products or obtain the ability to synthesize non-native products. This paper reviews the recent application of metabolic engineering in acetogens. In addition, the challenges of metabolic engineering in acetogens are indicated, and strategies to address these challenges are also discussed.

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.

Study on the lignin-derived sp2-sp3 hybrid hard carbon materials and the feasibility for industrial production

Hard carbon has been widely used in anode of lithium/sodium ion battery, electrode of supercapacitor, and carbon molecular sieve for CO2 capture and hydrogen storage. In this study the lignin derived hard carbon products are investigated, and the conclusions are abstracted as follows. (1) The lignin derived hard carbon products consist of microcrystal units of sp2 graphene fragments, jointed by sp3 carbon atoms and forming sp2-sp3 hybrid hard carbon family. (2) From the lignin precursors to the sp2-sp3 hybrid hard carbon products, most carbon atoms retain their original electron configurations (sp2 or sp3) and keep their composition in lignin. (3) The architectures of lignin-derived hard carbon materials are closely dependent on the forms of their lignin precursors, and could be preformed by different pretreatment techniques. (4) The carbonization of lignin precursors follows the mechanism "carbonization in situ and recombination nearby". (5) Due to the high carbon ratio and abundant active functional groups in lignin, new activation techniques could be developed for control of pore size and pore volume. In general lignin is an excellent raw material for sp2-sp3 hybrid hard carbon products, a green and sustainable alternative resource for phenolic resin, and industrial production for lignin derived hard carbon products would be feasible.

Microbial Upcycling of Depolymerized Lignin into Value-Added Chemicals

Lignin is one of the most widespread organic compounds found on earth, boasting a wealth of aromatic molecules. The use of lignin feedstock for biochemical productions is of great importance for achieving "carbon neutrality." In recent years, a strategy for lignin valorization known as the "bio-funnel" has been proposed as a means to generate a variety of commercially valuable chemicals from lignin-derived compounds. The implementation of biocatalysis and metabolic engineering techniques has substantially advanced the biotransformation of depolymerized lignin into chemicals and materials within the supply chain. In this review, we present an overview of the latest advancements in microbial upcycling of depolymerized lignin into value-added chemicals. Besides, the review provides insights into the problems facing current biological lignin valorization while proposing further research directions to improve these technologies for the extensive accomplishment of the lignin upcycling.

Whole-Genome Analysis of Termite-Derived Bacillus velezensis BV-10 and Its Application in King Grass Silage

Bacillus velezensis (B. velezensis) is a cellulose-degrading strain that has the potential as an additive in fermented feed. B. velezensis BV-10 was isolated and screened from the termite gut. We sequenced the whole genome of this new source of B. velezensis to reveal its potential for use in cellulose degradation. Whole-genome sequencing of B. velezensis BV-10 showed that it has a circular chromosome of 3929792 bp containing 3873 coding genes with a GC content of 45.51% and many genes related to cellulose, hemicellulose, and lignin degradation. King grass silage was inoculated with B. velezensis BV-10 and mixed with other feed additives to assess the effect of B. velezensis BV-10 on the fermentation quality of silage. Six treatment groups were established: the control, B. velezensis BV-10, molasses, cellulase, B. velezensis BV-10 plus molasses, and B. velezensis BV-10 plus cellulase groups. After 30 days of silage-fermentation testing, B. velezensis BV-10 was found to rapidly reduce the silage pH value and significantly reduce the acid-detergent fiber (ADF) content (p < 0.05). The addition of B. velezensis BV-10 plus molasses and cellulase in fermented feed significantly reduced the silage neutral-detergent fiber and ADF content and promoted organic-acid accumulation (p < 0.05). The above results demonstrate that B. velezensis BV-10 promotes the fermentation quality of silage and that this effect is greater when other silage-fermentation additives are included. In conclusion, genes involved in cellulose degradation in B. velezensis BV-10 were identified by whole-genome sequencing and further experiments explored the effects of B. velezensis BV-10 and different feed additives on the fermentation quality of king grass silage, revealing the potential of Bacillus velezensis as a new silage additive.

Recent progress of low-temperature plasma technology in biorefining process

In recent years, low-temperature plasma-assisted processes, featuring high reaction efficiency and wide application scope, have emerged as a promising alternative to conventional methods for biomass valorization. It is well established that charged species, chemically energetic molecules and radicals, and highly active photons playing key roles during processing. This review presents the major applications of low-temperature plasma for biomass conversion in terms of (i) pretreatment of biomass, (ii) chemo fractionation of biomass into value-added chemicals, and (iii) synthesis of heterogeneous catalyst for further chemo-catalytic conversion. The pretreatment of biomass is the first and foremost step for biomass upgrading to facilitate raw biomass transformation, which reduces the crystallinity, purification, and delignification. The chemo-catalytic conversion of biomass involves primary reactions to various kinds of target products, such as hydrolysis, hydrogenation, retro-aldol condensation and so on. Finally, recent researches on plasma-assisted chemo-catalysis as well as heterogeneous catalysts fabricated via low-temperature plasma at relatively mild condition were introduced. These catalysts were reported with comparable performance for biomass conversion to other state-of-the-art catalysts prepared using conventional methods.

Feasibility insights into the application of Paenibacillus pabuli E1 in animal feed to eliminate non-starch polysaccharides

The goal of the research was to find alternative protein sources for animal farming that are efficient and cost-effective. The researchers focused on distillers dried grains with solubles (DDGS), a co-product of bioethanol production that is rich in protein but limited in its use as a feed ingredient due to its high non-starch polysaccharides (NSPs) content, particularly for monogastric animals. The analysis of the Paenibacillus pabuli E1 genome revealed the presence of 372 genes related to Carbohydrate-Active enzymes (CAZymes), with 98 of them associated with NSPs degrading enzymes that target cellulose, hemicellulose, and pectin. Additionally, although lignin is not an NSP, two lignin-degrading enzymes were also examined because the presence of lignin alongside NSPs can hinder the catalytic effect of enzymes on NSPs. To confirm the catalytic ability of the degrading enzymes, an in vitro enzyme activity assay was conducted. The results demonstrated that the endoglucanase activity reached 5.37 U/mL, while beta-glucosidase activity was 4.60 U/mL. The filter paper experiments did not detect any reducing sugars. The xylanase and beta-xylosidase activities were measured at 11.05 and 4.16 U/mL, respectively. Furthermore, the pectate lyase and pectin lyase activities were found to be 8.19 and 2.43 U/mL, respectively. The activities of laccase and MnP were determined as 1.87 and 4.30 U/mL, respectively. The researchers also investigated the effect of P. pabuli E1 on the degradation of NSPs through the solid-state fermentation of DDGS. After 240 h of fermentation, the results showed degradation rates of 11.86% for hemicellulose, 11.53% for cellulose, and 8.78% for lignin. Moreover, the crude protein (CP) content of DDGS increased from 26.59% to 30.59%. In conclusion, this study demonstrated that P. pabuli E1 possesses various potential NSPs degrading enzymes that can effectively eliminate NSPs in feed. This process improves the quality and availability of the feed, which is important for animal farming as it seeks alternative protein sources to replace traditional nutrients.

Valorization of lignin for the production of vanillin by Bacillus aryabhattai NCIM 5503

Coconut coir waste is a rich lignocellulosic biomass. The coconut coir waste generated from temples is resistant to natural degradation, and its accumulation causes environmental pollution. Ferulic acid, a vanillin precursor, was extracted from the coconut coir waste by hydro-distillation extraction. The extracted ferulic acid was used for vanillin synthesis by Bacillus aryabhattai NCIM 5503 under submerged fermentation. In the present study, the Taguchi DOE (design of experiment) software was used to optimize the fermentation process, which resulted in a 1.3 fold increase in vanillin yield (640.96±0.02 mg/L), as compared to the unoptimized yield of 495.96±0.01 mg/L. The optimized media for enhanced vanillin production comprised; fructose 0.75 % (w/v), beef extract 1 % (w/v), pH 9, temperature 30℃, agitation speed 100 rpm, trace metal solution 1 % (v/v), and ferulic acid 2 % (v/v). The results show that the commercial production of vanillin can be envisioned using coconut coir waste.

Lignin to value-added products: Research updates and prospects

Due to the urgent need for renewable and clean energy, the efficient use of lignin is of wide interest. A comprehensive understanding of the mechanisms of lignin depolymerization and the generation of high-value products will contribute to the global control of the formation of efficient lignin utilization. This review explores the lignin value-adding process and discusses the link between lignin functional groups and value-added products. Mechanisms and characteristics of lignin depolymerization methods are presented, and challenges and prospects for future research are highlighted.

The Study of Potentially Lignocellulolytic Actinobacteria Pseudonocardia sp. AI2

The search for microorganisms with potential for bioconversion of lignocellulose is now of immediate interest. Industrial waste is a source of various microorganisms. This paper describes results of the research of potentially lignocellulolytic actinobacteria isolated from activated sludge of the wastewater treatment plant of a pulp and paper mill located in Komi Republic (Russia). One strain of actinobacteria, AI2, was found to be sufficiently active in terms of degradation of lignocellulose-containing materials. Testing of the AI2 isolate demonstrated its ability to synthesize cellulase, dehydrogenase and protease to various extents. The AI2 strain was found capable of biosynthesizing cellulase to 5.5 U/ml. In case of solid-phase fermentation using treated softwood and hardwood sawdust, the content of main components changed most significantly in aspen sawdust: from initial concentration of 20.4% down to 15.6% for lignin, and from 50.6% down to 31.8% for cellulose. In case of liquid-phase fermentation, the content of lignin components decreased significantly in the treated aqueous medium that contained lignosulfonates: from initial concentration of 3.6 g down to 2.1g. Taxonomic study of the AI2 strain of actinobacteria confirmed that it belongs to the rare Pseudonocardia genus of actinomycetes. Based on the results of 16S rRNA sequencing, the AI2 strain is most similar to the species Pseudonocardia carboxydivorans.

Reaching unreachables: Obstacles and successes of microbial cultivation and their reasons

In terms of the number and diversity of living units, the prokaryotic empire is the most represented form of life on Earth, and yet it is still to a significant degree shrouded in darkness. This microbial "dark matter" hides a great deal of potential in terms of phylogenetically or metabolically diverse microorganisms, and thus it is important to acquire them in pure culture. However, do we know what microorganisms really need for their growth, and what the obstacles are to the cultivation of previously unidentified taxa? Here we review common and sometimes unexpected requirements of environmental microorganisms, especially soil-harbored bacteria, needed for their replication and cultivation. These requirements include resuscitation stimuli, physical and chemical factors aiding cultivation, growth factors, and co-cultivation in a laboratory and natural microbial neighborhood.

Facultative anaerobic conversion of lignocellulose biomass to new bioemulsifier by thermophilic Geobacillus thermodenitrificans NG80-2

Heavy oil has hindered crude oil exploitation and pollution remediation due to its high density and viscosity. Bioemulsifiers efficiently facilitate the formation and stabilization of oil-in-water emulsions in low concentrations thus eliminating the above bottleneck. Despite their potential benefits, various obstacles had still impeded the practical applications of bioemulsifiers, including high purification costs and poor adaptability to extreme environments such as high temperature and oxygen deficiency. Herein, thermophilic facultative anaerobic Geobacillus thermodenitrificans NG80-2 was proved capable of emulsifying heavy oils and reducing their viscosity. An exocelluar bioemulsifier could be produced by NG80-2 using low-cost lignocellulose components as carbon sources even under anaerobic condition. The purified bioemulsifier was proved to be polysaccharide-protein complexes, and both components contributed to its emulsifying capability. In addition, it displayed excellent stress tolerance over wide ranges of temperatures, salinities, and pHs. Meanwhile, the bioemulsifier significantly improved oil recovery and degradation efficiency. An eps gene cluster for polysaccharide biosynthesis and genes for the covalently bonded proteins was further certificated. Therefore, the bioemulsifier produced by G. thermodenitrificans NG80-2 has immense potential for applications in bioremediation and EOR, and its biosynthesis pathway revealed here provides a theoretical basis for increasing bioemulsifier output.

Nature-inspired pretreatment of lignocellulose - Perspective and development

As sustainability gains increasing importance in addition to cost-effectiveness as a criterion for evaluating engineering systems and practices, biological processes for lignocellulose pretreatment have attracted growing attention. Biological systems such as white and brown rot fungi and wood-consuming insects offer fascinating examples of processes and systems built by nature to effectively deconstruct plant cell walls under environmentally benign and energy-conservative environments. Research in the last decade has resulted in new knowledge that advanced the understanding of these systems, provided additional insights into these systems' functional mechanisms, and demonstrated various applications of these processes. The new knowledge and insights enable the adoption of a nature-inspired strategy aiming at developing technologies that are informed by the biological systems but superior to them by overcoming the inherent weakness of the natural systems. This review discusses the nature-inspired perspective and summarizes related advancements, including the evolution from biological systems to nature-inspired processes, the features of biological pretreatment mechanisms, the development of nature-inspired pretreatment processes, and future perspective. This work aims to highlight a different strategy in the research and development of novel lignocellulose pretreatment processes and offer some food for thought.

Synthesis of honeycomb lignin-based biochar and its high-efficiency adsorption of norfloxacin

In this study, honeycomb lignin-based biochar (HLB) was prepared by hydrothermal activation using industrial lignin as raw material to remove norfloxacin from water. Batch adsorption test results showed that HLB has a strong ability to remove norfloxacin at a wide pH. The maximum adsorption capacity was 529.85 mg/g at 298 K, which is 1.52-fold to 201.46-fold higher than that of other reported materials. HLB showed good selectivity and recycling ability for the adsorption of norfloxacin, the removal rate of NOR reached 99.5% in the presence of competitive ions and maintained at least 98% removal rate after 12 adsorption cycles. The removal rate of norfloxacin in different water reached more than 99% within 8 mins. Pore filling, electrostatic interaction, π-π interaction, and hydrogen bond contributed significantly to the removal of norfloxacin. Among them, the highly aromatized structure of HLB and the abundant oxygen-containing functional groups (OH, CO, etc.) promoted π-π interaction.

Lignocellulolytic Biocatalysts: The Main Players Involved in Multiple Biotechnological Processes for Biomass Valorization

Human population growth, industrialization, and globalization have caused several pressures on the planet's natural resources, culminating in the severe climate and environmental crisis which we are facing. Aiming to remedy and mitigate the impact of human activities on the environment, the use of lignocellulolytic enzymes for biofuel production, food, bioremediation, and other various industries, is presented as a more sustainable alternative. These enzymes are characterized as a group of enzymes capable of breaking down lignocellulosic biomass into its different monomer units, making it accessible for bioconversion into various products and applications in the most diverse industries. Among all the organisms that produce lignocellulolytic enzymes, microorganisms are seen as the primary sources for obtaining them. Therefore, this review proposes to discuss the fundamental aspects of the enzymes forming lignocellulolytic systems and the main microorganisms used to obtain them. In addition, different possible industrial applications for these enzymes will be discussed, as well as information about their production modes and considerations about recent advances and future perspectives in research in pursuit of expanding lignocellulolytic enzyme uses at an industrial scale.

Improvement of thermoalkaliphilic laccase (CtLac) by a directed evolution and application to lignin degradation

Abstract

Thermoalkaliphilic laccase (CtLac) from the Caldalkalibacillus thermarum strain TA2.A1 has advantageous properties with potential industrial applications, such as high enzyme activity and stability at 70 °C and pH 8.0. In the present study, a directed evolution approach using a combination of random and site-directed mutagenesis was adopted to enhance the laccase activity of CtLac. Spectrophotometric assay and real-time oxygen measurement techniques were employed to compare and evaluate the enzyme activity among mutants. V243 was targeted for site-directed mutagenesis based on library screening. V243D showed a 25–35% higher laccase activity than wild-type CtLac in the spectrophotometric assay and oxygen consumption measurement results. V243D also showed higher catalytic efficiency than wild-type CtLac with decreased Km and increased kcat values. In addition, V243D enhanced oxidative degradation of the lignin model compound, guaiacylglycerol-β-guaiacyl ether (GGGE), by 10% and produced a 5–30% increase in high-value aldehydes than wild-type CtLac under optimal enzymatic conditions (i.e., 70 °C and pH 8.0). Considering the lack of protein structural information, we used the directed evolution approach to predict Val at the 243 position of CtLac as one of the critical amino acids contributing to the catalytic efficiency of the enzyme. Moreover, it found that the real-time oxygen measurement technique could overcome the limitations of the spectrophotometric assay, and apply to evaluate oxidase activity in mutagenesis research.

Key points

• CtLac was engineered for enhanced laccase activity through directed evolution approach

• V243D showed higher catalytic efficiency (kcat/Km) than wild-type CtLac

• V243D produced higher amounts of high-value aldehydes from rice straw than wild-type CtLac

Biotransformation of toxic lignin and aromatic compounds of lignocellulosic feedstock into eco-friendly biopolymers by Pseudomonas putida KT2440

Lignin and its derivatives are the most neglected compounds in bio-processing industry due to their toxic and recalcitrant nature. Considering this, the present study aimed at valorizing these toxic compounds by employing Pseudomonas putida KT2440. Acclimatization resulted in improved tolerance with considerable lag phase reduction and aromatics degradation. Glucose as co-substrate enhanced growth and degradation in the toxic environment. The strain was able to degrade 30 % (1.60 g·L^-1) lignin, 45 mM benzoate, 40 mM p-coumarate, 35 mM ferulate, 10 mM phenol, 10 mM pyrocatechol and 8 mM aromatics mixture. The strain synthesized biopolymers using these compounds under feast and famine conditions. Characterization using GC-MS, FT-IR, H¹ NMR revealed them to be Polyhydroxyalkanoate (PHA) heteropolymers. All the analyzed PHAs contained versatile monomers with Hexadecanoic acid being the major one. This is a novel attempt towards lignin and aromatics degradation coupled with biopolymers synthesis without any genetic manipulation of the strain.

Isolation and characterization of a novel thermotolerant alkali lignin-degrading bacterium Aneurinibacillus sp. LD3 and its application in food waste composting

The aim of this study was to isolate thermotolerant alkali lignin-degrading bacteria and to investigate their degradation characteristics and application in food waste composting. Two thermotolerant alkali lignin-degrading bacteria isolates were identified as Bacillus sp. LD2 (LD2) and a novel species Aneurinibacillus sp. LD3 (LD3). Compared with strain LD2, LD3 had a higher alkali lignin degradation rate (61.28%) and ligninolytic enzyme activities, and the maximum lignin peroxidase, laccase, and manganese peroxidase activities were 3117.25, 1484.5, and 1770.75 U L^-1, respectively. GC-MS analysis revealed that low-molecular-weight compounds such as 4'-hydroxy-3'-methoxy acetophenone, vanillic acid, 1-(4-hydroxy-3,5-dimethoxyphenyl), benzoic acid, and octadecanoic acid were formed in the degradation of alkali lignin by LD3, indicating the cleavage of β-aryl ether, C_α-C_β bonds, and aromatic rings in lignin. Composting results showed that inoculating LD3 improved the degradation of organic matter by 20.11% and reduced the carbon-to-nitrogen (C/N) ratio (15.66). Additionally, a higher decrease in the content of lignocellulose was observed in the LD treatment. FTIR and 3D-EEM spectra analysis indicated that inoculating LD3 promoted the decomposition of easily available organic substances and lignocellulose and the formation of aromatic structures and humic acid-like substances. In brief, the thermotolerant lignin-degrading bacterium Aneurinibacillus sp. LD3 is effective in degrading lignin and improving the quality of composting.

Recent Advancements and Challenges in Lignin Valorization: Green Routes towards Sustainable Bioproducts

The aromatic hetero-polymer lignin is industrially processed in the paper/pulp and lignocellulose biorefinery, acting as a major energy source. It has been proven to be a natural resource for useful bioproducts; however, its depolymerization and conversion into high-value-added chemicals is the major challenge due to the complicated structure and heterogeneity. Conversely, the various pre-treatments techniques and valorization strategies offers a potential solution for developing a biomass-based biorefinery. Thus, the current review focus on the new isolation techniques for lignin, various pre-treatment approaches and biocatalytic methods for the synthesis of sustainable value-added products. Meanwhile, the challenges and prospective for the green synthesis of various biomolecules via utilizing the complicated hetero-polymer lignin are also discussed.

Valorization of lignocellulosic biomass for polyhydroxyalkanoate production: Status and perspectives

With the increasing concerns regarding climate, energy, and plastic crises, bio-based production of biodegradable polymers has become a dire necessity. Significant progress has been made in biotechnology for the production of biodegradable polymers from renewable resources to achieve the goal of zero plastic waste and a net-zero carbon bioeconomy. In this review, an overview of polyhydroxyalkanoate (PHA) production from lignocellulosic biomass (LCB) was presented. Having established LCB-based biorefinery with proper pretreatment techniques, various PHAs could be produced from LCB-derived sugars, hydrolysates, and/or aromatic mixtures employing microorganisms. This provides a clue for addressing the current environmental crises because "biodegradable polymers" could be produced from one of the most abundant resources that are renewable and sustainable in a "carbon-neutral process". Furthermore, the potential future of LCB-to-non-natural PHA production was discussed with particular reference to non-natural PHA biosynthesis methods and LCB-derived aromatic mixture biofunnelling systems.

Green and Efficient Preparation of Tailed Lignin Nanoparticles and UV Shielding Composite Films

Lignin nanoparticles (LNP) with various morphologies could be prepared with solvent-antisolvent methods. However, the employed toxic chemicals limited its large-scale application. In this study, an extremely green method using only ethanol and water as solvent and antisolvent was reported. Besides, with the syringaldehyde (SA) addition and its anchoring action on the lignin particles, a forming process of the tailed structure was observed and resulted. Moreover, the improved electronegativity originating from the phenolic hydroxyl groups enhanced the size distribution uniformity, and the new absorption peaks at 1190 cm-1 demonstrated the involvement of SA in the LNP formation. Lastly, the tailed lignin nanoparticles (T-LNP) composited with, respectively, polyvinyl alcohol, chitosan, cellulose nanofibers, cationic etherified starch, and sodium alginate were successfully prepared. The outstanding UV-shielding and free radical scavenging properties in the above composites showed their great potential in wide applications in packaging materials.

Effect of whole-plant corn silage treated with lignocellulose-degrading bacteria on growth performance, rumen fermentation, and rumen microflora in sheep

Lignification of cellulose limits the effective utilisation of fibre in plant cell wall. Lignocellulose-degrading bacteria secrete enzymes that decompose lignin and have the potential to improve fibre digestibility. Therefore, this study aimed to investigate the effect of whole-plant corn silage inoculated with lignocellulose-degrading bacteria on the growth performance, rumen fermentation, and rumen microbiome in sheep. Twelve 2-month-old male hybrid sheep (Dorper ♂ × small-tailed Han ♀) were randomly assigned into two dietary groups (n = 6): (1) untreated whole-plant corn silage (WPCS) and (2) WPCS inoculated with bacterial inoculant (WPCSB). Whole-plant corn silage inoculated with bacterial inoculant had higher in situ NDF digestibility than WPCS. Sheep in the WPCSB group had significantly higher average daily gain, DM intake, and feed conversion rate than those in the WPCS group (P < 0.05). Furthermore, higher volatile fatty acid concentrations were detected in WPCSB rumen samples, leading to lower ruminal pH (P < 0.05). The WPCSB group showed higher abundance of Bacteroidetes and lower abundance of Firmicutes in the rumen microbiome than the WPCS group (P < 0.05). Multiple differential genera were identified, with Prevotella being the most dominant genus and more abundant in WPCSB samples. Moreover, the enriched functional attributes, including those associated with glycolysis/gluconeogenesis and citrate cycle, were more actively expressed in the WPCSB samples than in the WPCS samples. Additionally, certain glucoside hydrolases that hydrolyse the side chains of hemicelluloses and pectins were also actively expressed in the WPCSB microbiome. These findings suggested that WPCSB increased NDF digestibility in three ways: (1) by increasing the relative abundance of the most abundant genera, (2) by recruiting more functional features involved in glycolysis/gluconeogenesis and citrate cycle pathways, and (3) by increasing the relative abundance and/or expression activity of the glucoside hydrolases involved in hemicellulose and pectin metabolism. Our findings provide novel insights into the microbial mechanisms underlying improvement in the growth performance of sheep/ruminants. However, the biological mechanisms cannot be fully elucidated using only metagenomics tools; therefore, a combined multi-omics approach will be used in subsequent studies.

Recent advances in the treatment of lignin in papermaking wastewater

More than 695.7 million m³ of papermaking wastewater is discharged globally. It contains a mixture of complex pollutants, of which lignin is the major constituent (600-1000 mg/L) of papermaking black liquor, making it the second-largest energy-containing biomass globally and accounting for 47.4% and 59.4% of chemical oxygen demand (16,400 ± 120 mg/L) and chroma (3100 ± 22.32 mg/L) of papermaking wastewater. The complex process and dissolved pollutants are responsible for high pH, biochemical oxygen demand, chemical oxygen demand, total suspended solids, dark color, and toxicity. Papermaking wastewater has emerged as a substantial source of environmental pollution as the conventional wastewater treatment processes are high cost and seldom efficacious. This work introduces the shortcomings of the common treatment methods for papermaking wastewater and lignin, focusing on lignin biodegradation and discussing the metabolic pathways and application prospects of lignin-degrading microbial species. A comprehensive review of the existing lignin treatment methods has proposed that the reasonable amalgamation of biodegradation and various physicochemical techniques are environmentally friendly, sustainable, and economical. Lignin extraction from papermaking wastewater by technology combination is an effective approach to recover valuable organic materials and detoxify wastewater. This review focuses on recent breakthroughs and future trends in papermaking wastewater treatment and lignin removal, with special emphasis on biodegradation, recovery, and utilization of lignin, providing guidance for the mechanism exploration of lignin-degrading microorganisms and the optimization of high-value chemical production.

Whole-Genome Sequencing Reveals Lignin-Degrading Capacity of a Ligninolytic Bacterium (Bacillus cereus) from Buffalo (Bubalus bubalis) Rumen

The buffalo is an amazing ruminant. Its ability to degrade lignin, which has been recently reported, is most likely due to unique rumen microorganisms with lignin-degradation potential. Our goal was to explore the lignin-degradation potential of ruminal microorganisms, in which ligninolytic enzyme encoding genes were involved to provide ideas for revealing the mechanism of lignin degradation by buffalo. In this study, a bacterium strain identified as Bacillus cereus AH7-7 was isolated from the buffalo (Bubalus bubalis) rumen. After whole-genome sequencing, the results demonstrated that B. cereus AH7-7 had laccase, cytochrome P450 and vanillin alcohol oxidase-encoding genes. Sixty-four genes of B. cereus AH7-7 were involved in multiple aromatic metabolic pathways, such as phenylalanine metabolism and aminobenzoate degradation. A positive reaction resulting in guaiacol medium indicated that laccase secretion from B. cereus AH7-7 increased with time. A biodegradation experiment revealed that a significant reduction in kraft lignin content (25.9%) by B. cereus AH7-7 occurred at the end of 6 days of incubation, which confirmed its lignin-degradation capacity. Overall, this is the first report showing that B. cereus AH7-7 from the buffalo rumen can degrade lignin, and revealing the encoding genes of lignin-degrading enzymes from genome level.

Effective bioremediation of pulp and paper mill wastewater using Bacillus cereus as a possible kraft lignin-degrading bacterium

The effective degradation of KL from paper mill effluent is an important for environmental safety. This research is primarily concerned with the identification of KL-degrading Bacillus cereus from activated sludge and their possible use for the degradation of Kraft lignin (KL). This strain was involved in the production of lignin peroxidase-LiP (3.20 U/mL), manganese peroxidase-MnP (20.36 U/mL), and laccase (21.35 U/mL) enzymes, which were responsible for high KL degradation (89%) and decolorization (40%) at 1000 mg/L KL in 3 days. The SEM-EDS, UV-Vis, FTIR, and GC-MS analysis were used to analyze the bacterial cell and KL interactions to trace the KL degradation process. The significant reduction of pollutants (KL-72.5%, color-62.0%, COD-45.05%) and reduction in toxicity (80%) of bacterial-treated effluent indicated that B. cereus has the potential to be used in the degradation of pollutants from paper mill effluents.

Recent Biotechnology Advances in Bio-Conversion of Lignin to Lipids by Bacterial Cultures

The complexity and recalcitrance of the lignin structure is a major barrier to its efficient utilization and commercial production of high-value products. In recent years, the “bio-funneling” transformation ability of microorganisms has provided a significant opportunity for lignin conversion and integrated biorefinery. Based on the chemical structure of lignin, this mini-review introduces the recent advances of lignin depolymerization by bacterial strains and the application of microbial lignin degradation in lipids production. Furthermore, the current challenges, future trends and perspectives for microbe-based lignin conversion to lipids are discussed.

Effects of Microbial Inoculation with Different Indigenous Bacillus Species on Physicochemical Characteristics and Bacterial Succession during Short-Term Composting

Bacillus accelerates lignocellulose degradation, promotes the stabilization and resource utilization of compost by secreting enzymes, and plays an important role in compost formation and quality control. This study evaluated enzyme activity, lignocellulosic degradation, and bacterial succession in composting inoculated with different microbial Bacillus agents. They were identified as B. licheniformis, B. subtilis, B. thermoamylovorans, B. thermoruber, and B. hisashii. Four treatments were established, including a CK (uninoculated microorganisms), A (B. licheniformis, B. subtilis, B. thermoamylovorans,and B. hisashii), B (B. subtilis, B. thermoamylovorans, B. thermoruber, and B. hisashii), and C (B. subtilis, B. thermoamylovorans, and B. hisashii), and the composting lasted 7–14 days. Lignin and cellulose degradation rates in B during composting were 17.1% and 36.7% at the cooling stage, respectively. Redundancy analysis showed that degradation of lignocellulose in the thermophilic stage was mainly related to the secretion of lignocellulose-degrading enzymes after microbial inoculation. 16S rRNA sequencing revealed that Bacillus (20.3%) and Thermobifida (20.2%) were the dominant genera. Inoculation with a combination including B. thermoruber was a feasible way to increase lignocellulose degradation and promote maturity in sewage sludge composting.

Lignin degradation by microorganisms: A review

Lignin is an abundant plant-based biopolymer that has found applications in a variety of industries from construction to bioethanol production. This recalcitrant branched polymer is naturally degraded by many different species of microorganisms, including fungi and bacteria. These microbial lignin degradation mechanisms provide a host of possibilities to overcome the challenges of using harmful chemicals to degrade lignin biowaste in many industries. The classes and mechanisms of different microbial lignin degradation options available in nature form the primary focus of the present review. This review first discusses the chemical building blocks of lignin and the industrial sources and applications of this multifaceted polymer. The review further places emphasis on the degradation of lignin by natural means, discussing in detail the lignin degradation activities of various fungal and bacterial species. The lignin-degrading enzymes produced by various microbial species, specifically white-rot fungi, brown-rot fungi, and bacteria, are described. In the end, possible directions for future lignin biodegradation applications and research investigations have been provided.

Substitution of the Methionine Axial Ligand of the T1 Copper for the Fungal-like Phenylalanine Ligand (M298F) Causes Local Structural Perturbations that Lead to Thermal Instability and Reduced Catalytic Efficiency of the Small Laccase from Streptomyces coelicolor A3(2)

Many industrial processes operate at elevated temperatures or within broad pH and salinity ranges. However, the utilization of enzymes to carry out biocatalysis in such processes is often impractical or even impossible. Laccases (EC 1.10.3.2), which constitute a large family of multicopper oxidases, have long been used in the industrial setting. Although fungal laccases are in many respects considered superior to their bacterial counterparts, the bacterial laccases have been receiving greater attention recently. Albeit lower in redox potential than fungal laccases, bacterial laccases are commonly thermally more stable, act within broader pH ranges, do not contain posttranslational modifications, and could therefore serve as a high potential scaffold for directed evolution for the production of enzymes with enhanced properties. Several examples focusing on the axial ligand mutations of the T1 copper site have been published in the past. However, structural evidence on the local and global changes induced by those mutations have thus far been of computational nature only. In this study, we set out to structurally and kinetically characterize a few of the most commonly reported axial ligand mutations of a bacterial small laccase (SLAC) from Streptomyces coelicolor. While one of the mutations (Met to Leu) equips the enzyme with better thermal stability, the other (Met to Phe) induces an opposite effect. These mutations cause local structural rearrangement of the T1 site as demonstrated by X-ray crystallography. Our analysis confirms past findings that for SLACs, single point mutations that change the identity of the axial ligand of the T1 copper are not enough to provide a substantial increase in the catalytic efficiency but can in some cases have a detrimental effect on the enzyme's thermal stability parameters instead.

Trends in valorization of highly-toxic lignocellulosic biomass derived-compounds via engineered microbes

Lignocellulosic biomass-derived fuels, chemicals, and materials are promising sustainable solutions to replace the current petroleum-based production. The direct microbial conversion of thermos-chemically pretreated lignocellulosic biomass is hampered by the presence of highly toxic chemical compounds. Also, thermo-catalytic upgrading of lignocellulosic biomass generates wastewater that contains heterogeneous toxic chemicals, a mixture of unutilized carbon. Metabolic engineering efforts have primarily focused on the conversion of carbohydrates in lignocellulose biomass; substantial opportunities exist to harness value from toxic lignocellulose-derived toxic compounds. This article presents the comprehensive metabolic routes and tolerance mechanisms to develop robust synthetic microbial cell factories to valorize the highly toxic compounds to advanced-platform chemicals. The obtained platform chemicals can be used to manufacture high-value biopolymers and biomaterials via a hybrid biochemical approach for replacing petroleum-based incumbents. The proposed strategy enables a sustainable bio-based materials economy by microbial biofunneling of lignocellulosic biomass-derived toxic molecules, an untapped biogenic carbon.

Screening and Application of Ligninolytic Microbial Consortia to Enhance Aerobic Degradation of Solid Digestate

Recirculation of solid digestate through digesters has been demonstrated to be a potential simple strategy to increase continuous stirred-tank reactor biogas plant efficiency. This study extended this earlier work and investigated solid digestate post-treatment using liquid isolated ligninolytic aerobic consortia in order to increase methane recovery during the recirculation. Based on sampling in several natural environments, an enrichment and selection method was implemented using a Lab-scale Automated and Multiplexed (an)Aerobic Chemostat system to generate ligninolytic aerobic consortia. Then, obtained consortia were further cultivated under liquid form in bottles. Chitinophagia bacteria and Sordariomycetes fungi were the two dominant classes of microorganisms enriched through these steps. Finally, these consortia where mixed with the solid digestate before a short-term aerobic post-treatment. However, consortia addition did not increase the efficiency of aerobic post-treatment of solid digestate and lower methane yields were obtained in comparison to the untreated control. The main reason identified is the respiration of easily degradable fractions (e.g., sugars, proteins, amorphous cellulose) by the selected consortia. Thus, this paper highlights the difficulties of constraining microbial consortia to sole ligninolytic activities on complex feedstock, such as solid digestate, that does not only contain lignocellulosic structures.