Neutral and alkaline cellulases: Production, engineering, and applications

Exploration and origin studies of high levels of β-glucosidase in carnivorous fishes spotted knifejaw (Oplegnathus punctatus)

In order to more efficiently utilize the abundant cellulose resources in nature, increase the utilization rate of cellulose in aquaculture, implement precise feeding and save aquaculture costs, we have conducted research on cellulase genes related to the spotted knifejaw (Oplegnathus punctatus). Cellulose, as the most abundant renewable resource, is a cornerstone in the intricate ecological balance of diverse ecosystems. While herbivorous fish are recognized for their utilization of proteins, sugars, and fats, the extent of cellulose utilization by carnivorous and omnivorous fish remains an enigma. Here, through field sampling and behavioural observations, O. punctatus' omnivorous diet has been demonstrated (stomach contents contain approximately several species of algae in the Bacillariophyta (1.12 %), Streptomyces (0.55 %), Chlorophyta (0.35 %), Rhodophyta (0.16 %), and Euglenophyta (0.19 %) phylum). Additionally, the high cellulase activity in the intestine of O. punctatus has been detected first discovery (enzyme activity up to 4800.15 U/g), indicating its ability to digest cellulose. By employing whole-genome scanning and high-throughput sequencing, a single cellulase gene (β-glucosidase) within the genome of O. punctatus, suggesting the absence of a complete cellulose digestive system. However, microbiological analysis revealed the three crucial role of microorganisms, including Actinobacteria (25.80 %), Bacteroidetes (18.93 %), and Firmicutes phylum (0.82 %), were found to play a crucial role in the decomposition of plant cell walls, thereby facilitating plant material digestion to help the host to complete the process of cellulose digestion. Expression patterns and proteomic analysis of the β-glucosidase were notably high in the gonads. In situ hybridization confirmed the expression of the β-glucosidase gene in the intestinal contents and gonads, highlighting its role in supplying energy of gonads. These discoveries shed light on the dietary habits of O. punctatus and its cellulose utilization, offering insights that can inform the development of customized feeding strategies to enhance aquaculture sustainability and minimize resource expenditure.

Enhancement of cellulase production by cellulolytic bacteria SB125 in submerged fermentation medium and biochemical characterization of the enzyme

Microbial diversity from indigenous cultures has the potential to accelerate lignocellulose degradation through enzymes and make composting economically feasible. Therefore, this study is designed to boost cellulase output from a bacterial strain obtained from soil using a one-variable-at-a-time approach and response surface methodology. The bacteria recognized as Bacillus tequilensis (ON754229) produced the maximum cellulase at a temperature of 37 °C, pH -7.0, and incubation time of 72 h. A major contribution was anticipated by glucose (17 %) and ammonium sulfate (11 %) with cellulase activity of 0.56 U/mL in the optimized medium. The enzyme possessed activity of CMCase, FPase, and amylase of 0.589 μmol/min, 1.22 μmol/min, and 0.92 μmol/min respectively. SDS-PAGE showed a 65 kDa molecular weight of the enzyme capable of degrading cellulose, as confirmed by zymogram analysis. The enzyme showed relatively moderate thermo-stability towards neutral pH conditions possessing optimum conditions at pH 6.5 and temperature of 50 °C. The Km and Vmax values were 11.44 mM and 0.643 μmol/min respectively. The presence of MgSO4, ZnSO4, and Triton X- 100 increased the enzymatic reaction however AgNO3, EDTA, and HgCl2 altered the activation process. These results showed cellulase from B. tequilensis SB125 would be suitable for conventional industrial processes that convert biomass into biofuels.

Cloning and expression of Neurospora crassa cellobiohydrolase II in Pichia pastoris

A major cellobiohydrolase of Neurospora crassa CBH2 was successfully expressed in Pichia pastoris. The maximum Avicelase activity in shake flask among seven transformants which selected on 4.0 g/L G418 plates was 0.61 U/mL. The optimal pH and temperature for Avicelase activity of the recombinant CBH2 were determined to be 4.8 and 60 °C, respectively. The new CBH2 maintained 63.5 % Avicelase activity in the range of pH 4.0-10.4, and 60.2 % Avicelase activity in the range of 30-90 °C. After incubation at 70-90 °C for 1 h, the Avicelase activity retained 60.5 % of its initial activity. The presence of Zn2+, Ca2+ or Cd2+ enhanced the Avicelase activity of the CBH2, of which Cd2+ at 10 mM causing the highest increase. The recombinant CBH2 was used to enhance the Avicel hydrolysis by improving the exo-exo-synergism between CBH2 and CBH1 in N.crassa cellulase. The enzymatic hydrolysis yield was increased by 38.1 % by adding recombinant CBH2 and CBH1, and the yield was increased by 215.4 % when the temperature is raised to 70 °C. This work provided a CBH2 with broader pH range and better heat resistance, which is a potential enzyme candidate in food, textile, pulp and paper industries, and other industrial fields.

Engineering of glycoside hydrolase family 7 cellobiohydrolases directed by natural diversity screening

Protein engineering and screening of processive fungal cellobiohydrolases (CBHs) remain challenging due to limited expression hosts, synergy-dependency, and recalcitrant substrates. In particular, glycoside hydrolase family 7 (GH7) CBHs are critically important for the bioeconomy and typically difficult to engineer. Here, we target the discovery of highly active natural GH7 CBHs and engineering of variants with improved activity. Using experimentally assayed activities of genome mined CBHs, we applied sequence and structural alignments to top performers to identify key point mutations linked to improved activity. From ∼1500 known GH7 sequences, an evolutionarily diverse subset of 57 GH7 CBH genes was expressed in Trichoderma reesei and screened using a multiplexed activity screening assay. Ten catalytically enhanced natural variants were identified, produced, purified, and tested for efficacy using industrially relevant conditions and substrates. Three key amino acids in CBHs with performance comparable or superior to Penicillium funiculosum Cel7A were identified and combinatorially engineered into P. funiculosum cel7a, expressed in T. reesei, and assayed on lignocellulosic biomass. The top performer generated using this combined approach of natural diversity genome mining, experimental assays, and computational modeling produced a 41% increase in conversion extent over native P. funiculosum Cel7A, a 55% increase over the current industrial standard T. reesei Cel7A, and 10% improvement over Aspergillus oryzae Cel7C, the best natural GH7 CBH previously identified in our laboratory.

Recent advances in polysaccharide biomodification by microbial fermentation: production, properties, bioactivities, and mechanisms

Polysaccharides are natural chemical compounds that are extensively employed in the food and pharmaceutical industries. They exhibit a wide range of physical and biological properties. These properties are commonly improved by using chemical and physical methods. However, with the advancement of biotechnology and increased demand for green, clean, and safe products, polysaccharide modification via microbial fermentation has gained importance in improving their physicochemical and biological activities. The physicochemical and structural characteristics, biological activity, and modification mechanisms of microbially fermented polysaccharides were reviewed and summarized in this study. Polysaccharide modifications were categorized and discussed in terms of strains and fermentation techniques. The effects of microbial fermentation on the physicochemical characteristics of polysaccharides were highlighted. The impact of modification of polysaccharides on their antioxidant, immune, hypoglycemic, and other activities, as well as probiotic digestive enhancement, were also discussed. Finally, we investigated a potential enzyme-based process for polysaccharide modification via microbial fermentation. Modification of polysaccharides via microbial fermentation has significant value and application potential.

Multipurpose cellulases of Promicromonospora sp. VP111, with broad substrate specificity and tolerance properties

Cellulolytic actinobacterium, Promicromonospora sp. VP111 concomitantly produced cellulases (CELs), xylanase and pectinase when grown on commercial cellulose and untreated agricultural lignocellulosic residues (wheat straw and sugarcane bagasse). Secreted CELs hydrolyzed (enhanced with Co²⁺ ion) multiple cellulosic substrates, including sodium carboxymethyl cellulose (Na-CMC), Whatman filter paper no. 1, microcrystalline cellulose (avicel), p-nitrophenyl-β-D-glucopyranoside (pNPG), laminarin, and cellulose powder. The CELs showed stabilities in the presence of various chemicals, including glucose (0.2 M), detergents (1%, w/v or v/v), denaturants (1%, w/v or v/v), and sodium chloride (NaCl, 30%, w/v). The CELs were fractionated using ammonium sulfate precipitation and dialysis. Activities (%) of fractionated CELs were retained at 60°C for endoglucanase/carboxymethyl cellulase (CMCase) (88.38), filter paper cellulase (FPase) (77.55), and β-glucosidase (90.52), which indicated of thermo-stability. Similarly, the activities (%) for CMCase (85.79), FPase (82.48), and β-glucosidase (85.92) at pH 8.5 indicated of alkaline-stability. Kinetic factors, K_m and V_max for endoglucanase component of fractionated CELs were 0.014 g/l and 158.23 µM glucose/min/mL, respectively. Fractionated CELs yielded activation energies (kJ/mol) of 17.933, 6.294, and 4.207 for CMCase, FPase, and β-glucosidase activities, respectively in linear thermostable Arrhenius plots. Thus, this study reports on the multipurpose CELs from an untreated agricultural residue utilizing Promicromonospora in relation to broad substrate specificity, halo-tolerance, alkaline-tolerance, detergent-tolerance, thermo-tolerance, organic solvent-tolerance, and end product-tolerance.

Engineering cellulases for conversion of lignocellulosic biomass

Lignocellulosic biomass is a renewable source of energy, chemicals and materials. Many applications of this resource require the depolymerization of one or more of its polymeric constituents. Efficient enzymatic depolymerization of cellulose to glucose by cellulases and accessory enzymes such as lytic polysaccharide monooxygenases is a prerequisite for economically viable exploitation of this biomass. Microbes produce a remarkably diverse range of cellulases, which consist of glycoside hydrolase (GH) catalytic domains and, although not in all cases, substrate-binding carbohydrate-binding modules (CBMs). As enzymes are a considerable cost factor, there is great interest in finding or engineering improved and robust cellulases, with higher activity and stability, easy expression, and minimal product inhibition. This review addresses relevant engineering targets for cellulases, discusses a few notable cellulase engineering studies of the past decades and provides an overview of recent work in the field.

Discovery of novel carbohydrate degrading enzymes from soda lakes through functional metagenomics

Extremophiles provide a one-of-a-kind source of enzymes with properties that allow them to endure the rigorous industrial conversion of lignocellulose biomass into fermentable sugars. However, the fact that most of these organisms fail to grow under typical culture conditions limits the accessibility to these enzymes. In this study, we employed a functional metagenomics approach to identify carbohydrate-degrading enzymes from Ethiopian soda lakes, which are extreme environments harboring a high microbial diversity. Out of 21,000 clones screened for the five carbohydrate hydrolyzing enzymes, 408 clones were found positive. Cellulase and amylase, gave high hit ratio of 1:75 and 1:280, respectively. A total of 378 genes involved in the degradation of complex carbohydrates were identified by combining high-throughput sequencing of 22 selected clones and bioinformatics analysis using a customized workflow. Around 41% of the annotated genes belonged to the Glycoside Hydrolases (GH). Multiple GHs were identified, indicating the potential to discover novel CAZymes useful for the enzymatic degradation of lignocellulose biomass from the Ethiopian soda Lakes. More than 73% of the annotated GH genes were linked to bacterial origins, with Halomonas as the most likely source. Biochemical characterization of the three enzymes from the selected clones (amylase, cellulase, and pectinase) showed that they are active in elevated temperatures, high pH, and high salt concentrations. These properties strongly indicate that the evaluated enzymes have the potential to be used for applications in various industrial processes, particularly in biorefinery for lignocellulose biomass conversion.

Enhancement of catalytic activity and alkaline stability of cellobiohydrolase by structure-based protein engineering

Alkaline cellobiohydrolases have the potential for application in various industries, including pulp processing and laundry where operation under high pH conditions is preferred. In this study, variants of CtCel6A cellobiohydrolase from Chaetomium thermophilum were generated by structural-based protein engineering with the rationale of increasing catalytic activity and alkaline stability. The variants included removal of the carbohydrate-binding module (CBM) and substitution of residues 173 and 200. The CBM-deleted enzyme with Y200F mutation predicted to mediate conformational change at the N-terminal loop demonstrated increased alkaline stability at 60 °C, pH 8.0 for 24 h up to 2.25-fold compared with the wild-type enzyme. Another CBM-deleted enzyme with L173E mutation predicted to induce a new hydrogen bond in the substrate-binding cleft showed enhanced hydrolysis yield of pretreated sugarcane trash up to 4.65-fold greater than that of the wild-type enzyme at the pH 8.0. The variant enzymes could thus be developed for applications on cellulose hydrolysis and plant fiber modification operated under alkaline conditions.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13205-022-03339-4.

Halophilic and Halotolerant Actinomycetes of Sambhar Salt Lake, India: Screening and Optimization of Cellulolytic Activity

Actinomycetes are Gram-positive filamentous bacteria well known for the production of bioactive compounds. Recently, many halophilic habitats have been explored for isolation of actinomycetes that exhibit biotechnological potentials. In this investigation, a saline habitat of Rajasthan, Sambhar Salt Lake (SSL) was selected to study the actinomycetes population and Carboxy Methyl Cellulase (CMCase) production by native isolates. A total of sixteen actinomycete isolates, halotolerant and moderately halophilic, were obtained using culture-dependent methods and characterized morphologically and biochemically. They were identified as members of Streptomyces, Nocardiopsis, Pseudonocardia, Saccharospolyspora, and Microbispora. Streptomyces was the most dominating genus, followed by Nocardiopsis. Agar plate assay was used for screening the isolates for CMCase production. Thirteen were found to produce the enzyme, apparent by hydrolysis observed on media plates. The highest relative activity of 22.04 was shown by isolate SSL 14 identified as Nocardiopsis sp. by 16S rDNA sequencing studies and thus selected for further optimization studies. Maximum enzyme (1.08 ± 0.09 U/ml) was produced using medium containing Carboxy Methyl Cellulose (Carbon source) and yeast extract (nitrogen source) at 12% NaCl and pH 9.0, incubated at 30 °C for 96 h. Maximum CMCase production at high salt concentration and pH suggests that Nocardiopsis SSL 14 can be used for industrial processes that operate under excessive saline and alkaline conditions.

Expression, characterization, and activity optimization of a novel cellulase from the thermophilic bacteria Cohnella sp. A01

Cellulases are hydrolytic enzymes with wide scientific and industrial applications. We described a novel cellulase, CelC307, from the thermophilic indigenous Cohnella sp. A01. The 3-D structure of the CelC307 was predicted by comparative modeling. Docking of CelC307 with specific inhibitors and molecular dynamic (MD) simulation revealed that these ligands bound in a non-competitive manner. The CelC307 protein was purified and characterized after recombinant expression in Escherichia coli (E. coli) BL21. Using CMC 1% as the substrate, the thermodynamic values were determined as K_m 0.46 mM, k_cat 104.30 × 10^-3 (S^-1), and k_cat/K_m 226.73 (M^-1 S^-1). The CelC307 was optimally active at 40 °C and pH 7.0. The culture condition was optimized for improved CelC307 expression using Plackett-Burman and Box-Behnken design as follows: temperature 20 °C, pH 7.5, and inoculation concentration with an OD₆₀₀ = 1. The endoglucanase activity was positively modulated in the presence of Na⁺, Li⁺, Ca²⁺, 2-mercaptoethanol (2-ME), and glycerol. The thermodynamic parameters calculated for CelC307 confirmed its inherent thermostability. The characterized CelC307 may be a suitable candidate for various biotechnological applications.

Plant associated endophytic fungi as potential bio-factories for extracellular enzymes: Progress, Challenges and Strain improvement with precision approaches

There is an intricate network of relations between endophytic fungi and their hosts that affects the production of various bioactive compounds. Plant-associated endophytic contain industrially important enzymes and have the potential to fulfill their rapid demand in the international market to boost business in technology. Being safe and metabolically active, they have replaced the usage of toxic and harmful chemicals and hold a credible application in biotransformation, bioremediation, and industrial processes. Despite these, there are limited reports on fungal endophytes that can directly cater to the demand and supply of industrially stable enzymes. The underlying reasons include low endogenous production and secretion of enzymes from fungal endophytes which have raised concern for widely accepted applications. Hence it is imperative to augment the biosynthetic and secretory potential of fungal endophytes. Modern state-of-the-art biotechnological technologies aiming at strain improvement using cell factory engineering as well as precise gene editing like Clustered Regularly Interspaced Palindromic Repeats (CRISPR) and its Associated proteins (Cas) systems which can provide a boost in fungal endophyte enzyme production. Additionally, it is vital to characterize optimum conditions to grow one strain with multiple enzymes (OSME). The present review encompasses various plants-derived endophytic fungal enzymes and their applications in various sectors. Further, we postulate the feasibility of new precision approaches with an aim for strain improvement and enhanced enzyme production.

Coconut Mesocarp-Based Lignocellulosic Waste as a Substrate for Cellulase Production from High Promising Multienzyme-Producing Bacillus amyloliquefaciens FW2 without Pretreatments

Facing the crucial issue of high cost in cellulase production from commercial celluloses, inexpensive lignocellulosic materials from agricultural wastes have been attractive. Therefore, several studies have focused on increasing the efficiency of cellulase production by potential microorganisms capable of secreting a high and diversified amount of enzymes using agricultural waste as valuable substrates. Especially, extremophilic bacteria play an important role in biorefinery due to their high value catalytic enzymes that are active even under harsh environmental conditions. Therefore, in this study, we aim to investigate the ability to produce cellulase from coconut-mesocarp of the potential bacterial strain FW2 that was isolated from kitchen food waste in South Korea. This strain was tolerant in a wide range of temperature (−6–75 °C, pH range (4.5–12)) and at high salt concentration up to 35% NaCl. The molecular weight of the purified cellulase produced from strain FW2 was estimated to be 55 kDa. Optimal conditions for the enzyme activity using commercial substrates were found to be 40–50 °C, pH 7.0–7.5, and 0–10% NaCl observed in 920 U/mL of CMCase, 1300 U/mL of Avicelase, and 150 U/mL of FPase. It was achieved in 650 U/mL, 720 U/mL, and 140 U/mL of CMCase, Avicelase, and FPase using coconut-mesocarp, respectively. The results revealed that enzyme production by strain FW2 may have significant commercial values for industry, argo-waste treatment, and other potential applications.

Natural Products of the Fungal Genus Humicola: Diversity, Biological Activity, and Industrial Importance

Fungal metabolites are worthily taken into account as a pool of synthetically interesting and remarkably important new lead compounds for medical, agricultural, and chemical industries. Humicola species are known to have biotechnological and industrial potentials. Humicola genus (family Chaetomiaceae) is a prosperous fountainhead of unique and structurally diverse metabolites that have various bioactivities. Moreover, Humicola species attract substantial attention for their marked ability to produce thermostable enzymes with biotechnological and industrial importance. This review highlights the published researches on the isolated metabolites from the genus Humicola and their biological activities as well as the industrial importance of Humicola species. In the current review, more than 50 compounds are described and 84 references are cited.

Molecular and biochemical characterization of a recombinant endoglucanase rCKT3eng, from an extreme halophilic Haloarcula sp. strain CKT3

Halophilic cellulases are indispensable enzymes of heavy industrial processes as resistant biocatalysts due to high level activity at extreme conditions. In this study, crude cellulase from an extreme halophilic Haloarcula sp. CKT3 was characterized. Then, recombinant expression of putative endo-1,4-β-glucanase gene, of CKT3 strain, in E. coli BL21(DE3) was performed with the aim of obtaining highly pure, active and robust industrial enzyme for such industrial aplications. The crude cellulase had optimal activity (16.9 U/mg) at 70 °C, pH 7.0 and 4 M NaCl exhibiting good thermostability, high pH and halotolerance. Indeed, it is very stable in water-insoluble organic solvents with log P_o/w ≥ 2.13 and highly resistant to SDS (10%). Recombinant CKT3eng has a molecular weight of 36.9 kDa and 99% aminoacid identity to endo-l,4-β-D-glucanase from Haloarcula argentinensis. Its 3D structure was predicted using Phyre2 and I-TASSER. rCKT3eng enzyme provided 31.6 U/mg activity at optimal 50 °C, pH 7.0 and 3 M NaCl. In addition to its quite similar stability values and resistance to organic solvents and SDS, rCKT3eng has superiority over crude enzyme with 1.87-fold higher specific activity. Therefore, rCKT3eng offers a promising enzyme for industrial use with its valuable activity and stability in extreme conditions.

Recombinant expression and characterization of two glycoside hydrolases from extreme alklinphilic bacterium Cellulomonas bogoriensis 69B4T

Two novel glycoside hydrolases were cloned from the genomic DNA of alklinphilic bacterium Cellulomonas bogoriensis 69B4^T and functionally expressed in Escherichia coli. The two enzymes shared less than 73% of identities with other known glycosidases and belonged to glycoside hydrolase families 5 and 9. Recombinant Cel5A exhibited optimum activity at pH 5.0 and at a temperature of 70 °C, and Cel9A showed optimum activity at pH 7.0 and at a temperature of 60 °C. The two enzymes exhibited activity at alkaline pH 11 and were stable over a wide range of pH. The maximum activities of Cel5A and Cel9A were observed in 0.5 M NaCl and 1 M KCl, respectively. In addition, these two enzymes exhibited excellent halostability with residual activities of more than 70% after pre-incubation for 6 days in 5 M NaCl or 4 M KCl. Substrate specificity analysis revealed that Cel5A and Cel9A specifically cleaved the β-1,4-glycosidic linkage in cellulose with the highest activity on carboxymethyl cellulose sodium (78.3 and 145.3 U/mg, respectively). Cel5A is an endoglucanase, whereas Cel9A exhibits endo and exo activities. As alkali-activated, thermo-tolerant, and salt-tolerant cellulases, Cel5A and Cel9A are promising candidates for further research and industrial applications.

Validation of leaf enzymes in the detergent and textile industries: launching of a new platform technology

Chemical catalysts are being replaced by biocatalysts in almost all industrial applications due to environmental concerns, thereby increasing their demand. Enzymes used in current industries are produced in microbial systems or plant seeds. We report here five newly launched leaf-enzyme products and their validation with 15 commercial microbial-enzyme products, for detergent or textile industries. Enzymes expressed in chloroplasts are functional at broad pH/temperature ranges as crude-leaf extracts, while most purified commercial enzymes showed significant loss at alkaline pH or higher temperature, required for broad range commercial applications. In contrast to commercial liquid enzymes requiring cold storage/transportation, chloroplast enzymes as a leaf powder can be stored up to 16 months at ambient temperature without loss of enzyme activity. Chloroplast-derived enzymes are stable in crude-leaf extracts without addition of protease inhibitors. Leaf lipase/mannanase crude extracts removed chocolate or mustard oil stains effectively at both low and high temperatures. Moreover, leaf lipase or mannanase crude-extracts removed stain more efficiently at 70 °C than commercial microbial enzymes (<10% activity). Endoglucanase and exoglucanase in crude leaf extracts removed dye efficiently from denim surface and depilled knitted fabric by removal of horizontal fibre strands. Due to an increased demand for enzymes in the food industry, marker-free lettuce plants expressing lipase or cellobiohydrolase were created for the first time and site-specific transgene integration/homoplasmy was confirmed by Southern blots. Thus, leaf-production platform offers a novel low-cost approach by the elimination of fermentation, purification, concentration, formulation and cold-chain storage/transportation. This is the first report of commercially launched protein products made in leaves and validated with current commercial products.

Contemporary enzyme based technologies for bioremediation: A review

The persistent disposal of xenobiotic compounds like insecticides, pesticides, fertilizers, plastics and other hydrocarbon containing substances is the major source of environmental pollution which needs to be eliminated. Many contemporary remediation methods such as physical, chemical and biological are currently being used, but they are not sufficient to clean the environment. The enzyme based bioremediation is an easy, quick, eco-friendly and socially acceptable approach used for the bioremediation of these recalcitrant xenobiotic compounds from the natural environment. Several microbial enzymes with bioremediation capability have been isolated and characterized from different natural sources, but less production of such enzymes is a limiting their further exploitation. The genetic engineering approach has the potential to get large amount of recombinant enzymes. Along with this, enzyme immobilization techniques can boost the half-life, stability and activity of enzymes at a significant level. Recently, nanozymes may offer the potential bioremediation ability towards a broad range of pollutants. In the present review, we have described a brief overview of the microbial enzymes, different enzymes techniques (genetic engineering and immobilization of enzymes) and nanozymes involved in bioremediation of toxic, carcinogenic and hazardous environmental pollutants.