Characterization of cellobiose dehydrogenase and its FAD-domain from the ligninolytic basidiomycete Pycnoporus sanguineus

Surface display system of Bacillus subtilis: A promising approach for improving the stability and applications of cellobiose dehydrogenase

Cellobiose dehydrogenase (CDH) plays a crucial role in lignocellulose degradation and bioelectrochemical industries, making it highly in demand. However, the production and purification of CDH through fungal heterologous expression methods is time-consuming, costly, and challenging. In this study, we successfully displayed Pycnoporus sanguineus CDH (psCDH) on the surface of Bacillus subtilis spores for the first time. Enzymatic characterization revealed that spore surface display enhanced the tolerance of psCDH to high temperature (80 °C) and low pH levels (3.5) compared to free psCDH. Furthermore, we found that glycerol, lactic acid, and malic acid promoted the activity of immobilized spore-displayed psCDH; glycerol has a more significant stimulating effect, increasing the activity from 16.86 ± 1.27 U/mL to 46.26 ± 3.25 U/mL. After four reuse cycles, the psCDH immobilized with spores retained 48% of its initial activity, demonstrating a substantial recovery rate. In conclusion, the spore display system, relying on cotG, enables the expression and immobilization of CDH while enhancing its resistance to adverse conditions. This system demonstrates efficient enzyme recovery and reuse. This approach provides a novel method and strategy for the immobilization and stability enhancement of CDH.

Exploring class III cellobiose dehydrogenase: sequence analysis and optimized recombinant expression

BACKGROUND

Cellobiose dehydrogenase (CDH) is an extracellular fungal oxidoreductase with multiple functions in plant biomass degradation. Its primary function as an auxiliary enzyme of lytic polysaccharide monooxygenase (LPMO) facilitates the efficient depolymerization of cellulose, hemicelluloses and other carbohydrate-based polymers. The synergistic action of CDH and LPMO that supports biomass-degrading hydrolases holds significant promise to harness renewable resources for the production of biofuels, chemicals, and modified materials in an environmentally sustainable manner. While previous phylogenetic analyses have identified four distinct classes of CDHs, only class I and II have been biochemically characterized so far.

RESULTS

Following a comprehensive database search aimed at identifying CDH sequences belonging to the so far uncharacterized class III for subsequent expression and biochemical characterization, we have curated an extensive compilation of putative CDH amino acid sequences. A sequence similarity network analysis was used to cluster them into the four distinct CDH classes. A total of 1237 sequences encoding putative class III CDHs were extracted from the network and used for phylogenetic analyses. The obtained phylogenetic tree was used to guide the selection of 11 cdhIII genes for recombinant expression in Komagataella phaffii. A small-scale expression screening procedure identified a promising cdhIII gene originating from the plant pathogen Fusarium solani (FsCDH), which was selected for expression optimization by signal peptide shuffling and subsequent production in a 5-L bioreactor. The purified FsCDH exhibits a UV-Vis spectrum and enzymatic activity similar to other characterized CDH classes.

CONCLUSION

The successful production and functional characterization of FsCDH proved that class III CDHs are catalytical active enzymes resembling the key properties of class I and class II CDHs. A detailed biochemical characterization based on the established expression and purification strategy can provide new insights into the evolutionary process shaping CDHs and leading to their differentiation into the four distinct classes. The findings have the potential to broaden our understanding of the biocatalytic application of CDH and LPMO for the oxidative depolymerization of polysaccharides.

Staphylococcus aureus microbial biofilms degradation using cellobiose dehydrogenase from Thermothelomyces thermophilus M77

This work reports biochemical characterization of Thermothelomyces thermophilus cellobiose dehydrogenase (TthCDHIIa) and its application as an antimicrobial and antibiofilm agent. We demonstrate that TthCDHIIa is thermostable in different ionic solutions and is capable of oxidizing multiple mono and oligosaccharide substrates and to continuously produce H2O2. Kinetics measurements depict the enzyme catalytic characteristics consistent with an Ascomycota class II CDH. Our structural analyses show that TthCDHIIa substrate binding pocket is spacious enough to accommodate larger cello and xylooligosaccharides. We also reveal that TthCDHIIa supplemented with cellobiose reduces the viability of S. aureus ATCC 25923 up to 32 % in a planktonic growth model and also inhibits its biofilm growth on 62.5 %. Furthermore, TthCDHIIa eradicates preformed S. aureus biofilms via H2O2 oxidative degradation of the biofilm matrix, making these bacteria considerably more susceptible to gentamicin and tetracycline.

Chitosan as a Promising Support of a CDH Activity Preservation System for Biomedical and Industrial Applications

Cellobiose dehydrogenase (CDH) is an extracellular hemoflavoprotein catalyzing the oxidation reaction of β-1,4-glycosidic-bonded sugars (lactose or cellobiose), which results in the formation of aldobionic acids and hydrogen peroxide as a byproduct. The biotechnological application of CDH requires the immobilization of the enzyme on a suitable support. As a carrier of natural origin used for CDH immobilization, chitosan seems to increase the catalytic potential of the enzyme, especially for applications as packaging in the food industry and as a dressing material in medical applications. The present study aimed to immobilize the enzyme on chitosan beads and determine the physicochemical and biological properties of immobilized CDHs obtained from different fungal sources. The chitosan beads with immobilized CDHs were characterized in terms of their FTIR spectra or SEM microstructure. The most effective method of immobilization in the proposed modification was the covalent bonding of enzyme molecules using glutaraldehyde, resulting in efficiencies ranging from 28 to 99%. Very promising results, compared to free CDH, were obtained in the case of antioxidant, antimicrobial, and cytotoxic properties. Summarizing the obtained data, chitosan seems to be a valuable material for the development of innovative and effective immobilization systems for biomedical applications or food packaging, preserving the unique properties of CDH.

Natural microbial polysaccharides as effective factors for modification of the catalytic properties of fungal cellobiose dehydrogenase

Polysaccharides are biopolymers composed of simple sugars like glucose, galactose, mannose, fructose, etc. The major natural sources for the production of polysaccharides include plants and microorganisms. In the present work, four bacterial and two fungal polysaccharides (PS or EPS) were used for the modification and preservation of Pycnoporus sanguineus cellobiose dehydrogenase (CDH) activity. It was found that the presence of polysaccharide preparations clearly enhanced the stability of cellobiose dehydrogenase compared to the control value (4 °C). The highest stabilization effect was observed for CDH modified with Rh110EPS. Changes in the optimum pH in the samples of CDH incubated with the chosen polysaccharide modifiers were evidenced as well. The most significant effect was observed for Rh24EPS and Cu139PS (pH 3.5). Cyclic voltammetry used for the analysis of electrochemical parameters of modified CDH showed the highest peak values after 30 days of incubation with polysaccharides at 4 °C. In summary, natural polysaccharides seem to be an effective biotechnological tool for the modification of CDH activity to increase the possibilities of its practical applications in many fields of industry.

Oxalate oxidase from Abortiporus biennis - protein localisation and gene sequence analysis

We have described for the first time the localisation of oxalate oxidase (OXO, EC 1.2.3.4) in Abortiporus biennis cells, using histochemical and immunochemical methods coupled with transmission electron microscopy. Rabbit anti-oxalate oxidase immunoglobulins with anti-rabbit secondary antibody conjugated with 10-nm gold particles were used. Moreover, the formation of electron dense precipitation of reaction of diaminobenzidine (DAB) with horseradish peroxidase (HRP) for histochemical localisation of the enzyme was found. OXO was localised close to the membranous structures of the cell membranes, in membranous vesicles located close to the outer cell membrane, and vacuolar membranes surrounding vacuoles. The positive immunoreaction to OXO was also intense in cell wall areas. Moreover, we proved that gene coding for OXO was expressed in the same cultures. Corresponding mRNA was isolated, full length cDNA was synthesized, cloned and sequenced. Two copies of cupin domains were found in the sequence of amino-acids conserved domain coding for the cupin enzyme. Comparison of the genomic DNA and cDNA sequences has revealed the presence of seventeen introns in the gene. The isoelectric point of the protein was estimated at pH 4.5 and several possible N-glycosylation sites were predicted.

Complex Biochemical Analysis of Fruiting Bodies from Newly Isolated Polish Flammulina velutipes Strains

The present study examined Polish strains of Flamulina velutipes as a potential source of nutraceuticals and found that their nutritional value is dependent on the fruiting bodies gathering time. To prove the above hypothesis protein, carbohydrate and phenolic substances concentration were determined. Moreover, catalase, superoxide dismutase, cellobiose dehydrogenase activities were assayed. In order to prove the healing properties of Enoki fruiting bodies the obtained extracts were tested for antioxidant and bacteriostatic abilities. We have proved that Polish F. velutipes fruiting bodies may be a rich source of antioxidants and that they are capable of inhibiting Staphylococcus aureus growth.

Inactivation of Cellobiose Dehydrogenases Modifies the Cellulose Degradation Mechanism of Podospora anserina

Conversion of biomass into high-value products, including biofuels, is of great interest to developing sustainable biorefineries. Fungi are an inexhaustible source of enzymes to degrade plant biomass. Cellobiose dehydrogenases (CDHs) play an important role in the breakdown through synergistic action with fungal lytic polysaccharide monooxygenases (LPMOs). The three CDH genes of the model fungus Podospora anserina were inactivated, resulting in single and multiple CDH mutants. We detected almost no difference in growth and fertility of the mutants on various lignocellulose sources, except on crystalline cellulose, on which a 2-fold decrease in fertility of the mutants lacking P. anserina CDH1 (PaCDH1) and PaCDH2 was observed. A striking difference between wild-type and mutant secretomes was observed. The secretome of the mutant lacking all CDHs contained five beta-glucosidases, whereas the wild type had only one. P. anserina seems to compensate for the lack of CDH with secretion of beta-glucosidases. The addition of P. anserina LPMO to either the wild-type or mutant secretome resulted in improvement of cellulose degradation in both cases, suggesting that other redox partners present in the mutant secretome provided electrons to LPMOs. Overall, the data showed that oxidative degradation of cellulosic biomass relies on different types of mechanisms in fungi.

IMPORTANCE

Plant biomass degradation by fungi is a complex process involving dozens of enzymes. The roles of each enzyme or enzyme class are not fully understood, and utilization of a model amenable to genetic analysis should increase the comprehension of how fungi cope with highly recalcitrant biomass. Here, we report that the cellobiose dehydrogenases of the model fungus Podospora anserina enable it to consume crystalline cellulose yet seem to play a minor role on actual substrates, such as wood shavings or miscanthus. Analysis of secreted proteins suggests that Podospora anserina compensates for the lack of cellobiose dehydrogenase by increasing beta-glucosidase expression and using an alternate electron donor for LPMO.

Purification and characterization of laccase from Sinorhizobium meliloti and analysis of the lacc gene

The soil native bacterial strains were screened for laccase activity. Bacterial strain L3.8 with high laccase activity was identified as Sinorhizobium meliloti. The crude intracellular L3.8 enzyme extract was able to oxidize typical diagnostic substrates of plant and fungal laccases. Laccase L3.8 was purified 81-fold with a yield of 19.5%. The molecular mass of the purified bacterial laccase was found to be 70.0kDa and its pI was 4.77. UV-vis spectrum showed that L3.8 protein is a multicopper oxidase. The carbohydrate content of the purified enzyme was estimated at 3.2%. Moreover, the laccase active fraction was characterized in terms of kinetics, temperature, and pH optima as well as the effect of various chemical compounds on the laccase activity, and antioxidant properties, which indicated that the L3.8 laccase had unique properties that might be important in biotechnological applications. The lacc gene encoding S. meliloti laccase was cloned and characterized. The full-length sequence of 1950bp encoded a protein of 649 aa preceded by a signal peptide consisting of 26aa. Laccase L3.8 shared significant structural features characteristic of other laccases, including the conserved regions of four histidine-rich copper-binding sites. Potential biotechnological importance of a newly identified laccase is discussed.

Characterization of Cellobiose Dehydrogenase from a Biotechnologically Important Cerrena unicolor Strain

Cellobiose dehydrogenase (CDH), a secreted flavocytochrome produced by a number of wood-degrading fungi, was detected in the culture supernatant of a biotechnologically important strain of Cerrena unicolor grown in a modified cellulose-based liquid medium. The enzyme was purified as two active fractions: CuCDH-FAD (flavin domain) (1.51-fold) with recovery of 8.35 % and CuCDH (flavo-heme enzyme) (21.21-fold) with recovery of 73.41 %. As CDH from other wood-rotting fungi, the intact form of cellobiose dehydrogenase of C. unicolor is a monomeric protein containing one flavin and one heme b with molecular mass 97 kDa and pI = 4.55. The enzyme is glycosylated (8.2 %) mainly with mannose and glucosamine residues. Moreover, the cellobiose dehydrogenase gene cdh1 and its corresponding cDNA from the fungus C. unicolor were isolated, cloned, and characterized. The 2316-bp full-length cDNA of cdh1 encoded a mature CDH protein containing 771 amino acids preceded by a signal peptide consisting of 18 amino acids. Moreover, both active fractions were characterized in terms of kinetics, temperature and pH optima, and antioxidant properties.

Plant-polysaccharide-degrading enzymes from Basidiomycetes

SUMMARY

Basidiomycete fungi subsist on various types of plant material in diverse environments, from living and dead trees and forest litter to crops and grasses and to decaying plant matter in soils. Due to the variation in their natural carbon sources, basidiomycetes have highly varied plant-polysaccharide-degrading capabilities. This topic is not as well studied for basidiomycetes as for ascomycete fungi, which are the main sources of knowledge on fungal plant polysaccharide degradation. Research on plant-biomass-decaying fungi has focused on isolating enzymes for current and future applications, such as for the production of fuels, the food industry, and waste treatment. More recently, genomic studies of basidiomycete fungi have provided a profound view of the plant-biomass-degrading potential of wood-rotting, litter-decomposing, plant-pathogenic, and ectomycorrhizal (ECM) basidiomycetes. This review summarizes the current knowledge on plant polysaccharide depolymerization by basidiomycete species from diverse habitats. In addition, these data are compared to those for the most broadly studied ascomycete genus, Aspergillus, to provide insight into specific features of basidiomycetes with respect to plant polysaccharide degradation.

Laccase production and metabolic diversity among Flammulina velutipes strains

Twelve Flammulina velutipes strains originating from Poland were identified using internal transcribed spacer (ITS) region sequencing. Based on the sequences obtained, the genomic relationship of the analyzed strains was determined. All F. velutipes strains were also characterized using Biolog FF MicroPlates to obtain data on C-substrate utilization and mitochondrial activity. The ability to decompose various substrates differed among the F. velutipes strains up to five times. The highest catabolic activities were characteristic for only two strains with capabilities to decompose up to 22 carbon sources. The correlation between carbon repression and laccase production by F. velutipes was analyzed based on glucose assimilation by these strains. Moreover, the influence of metal ions (Cu(2+), Cd(2+)), veratric and ferulic acids, and temperature on laccase activities in the analyzed strains was determined. The results obtained proved that all the inducers influenced laccase expression in almost all the analyzed strains. However, the degree of induction depended not only on the strain used but also on the day of the induction.