Synergy between EngE, XynA and ManA from Clostridium cellulovorans on corn stalk, grass and pineapple pulp substrates

Towards an understanding of the enzymatic degradation of complex plant mannan structures

Plant cell walls are composed of a heterogeneous mixture of polysaccharides that require several different enzymes to degrade. These enzymes are important for a variety of biotechnological processes, from biofuel production to food processing. Several classical mannanolytic enzyme functions of glycoside hydrolases (GH), such as β-mannanase, β-mannosidase and α-galactosidase activities, are helpful for efficient mannan hydrolysis. In this light, we bring three enzymes into the model of mannan degradation that have received little or no attention. By linking their three-dimensional structures and substrate specificities, we have predicted the interactions and cooperativity of these novel enzymes with classical mannanolytic enzymes for efficient mannan hydrolysis. The novel exo-β-1,4-mannobiohydrolases are indispensable for the production of mannobiose from the terminal ends of mannans, this product being the preferred product for short-chain mannooligosaccharides (MOS)-specific β-mannosidases. Second, the side-chain cleaving enzymes, acetyl mannan esterases (AcME), remove acetyl decorations on mannan that would have hindered backbone cleaving enzymes, while the backbone cleaving enzymes liberate MOS, which are preferred substrates of the debranching and sidechain cleaving enzymes. The nonhydrolytic expansins and swollenins disrupt the crystalline regions of the biomass, improving their accessibility for AcME and GH activities. Finally, lytic polysaccharide monooxygenases have also been implicated in promoting the degradation of lignocellulosic biomass or mannan degradation by classical mannanolytic enzymes, possibly by disrupting adsorbed mannan residues. Modelling effective enzymatic mannan degradation has implications for improving the saccharification of biomass for the synthesis of value-added and upcycling of lignocellulosic wastes.

Enzymatic Characterization of Unused Biomass Degradation Using the Clostridium cellulovorans Cellulosome

The cellulolytic system of Clostridium cellulovorans mainly consisting of a cellulosome that synergistically collaborates with non-complexed enzymes was investigated using cellulosic biomass. The cellulosomes were isolated from the culture supernatants with shredded paper, rice straw and sugarcane bagasse using crystalline cellulose. Enzyme solutions, including the cellulosome fractions, were analyzed by SDS-PAGE and Western blot using an anti-CbpA antibody. As a result, C. cellulovorans was able to completely degrade shredded paper for 9 days and to be continuously cultivated by the addition of new culture medium containing shredded paper, indicating, through TLC analysis, that its degradative products were glucose and cellobiose. Regarding the rice straw and sugarcane bagasse, while the degradative activity of rice straw was most active using the cellulosome in the culture supernatant of rice straw medium, that of sugarcane bagasse was most active using the cellulosome from the supernatant of cellobiose medium. Based on these results, no alcohols were found when C. acetobutylicum was cultivated in the absence of C. cellulovorans as it cannot degrade the cellulose. While 1.5 mM of ethanol was produced with C. cellulovorans cultivation, both n-butanol (1.67 mM) and ethanol (1.89 mM) were detected with the cocultivation of C. cellulovorans and C. acetobutylicum. Regarding the enzymatic activity evaluation against rice straw and sugarcane bagasse, the rice straw cellulosome fraction was the most active when compared against rice straw. Furthermore, since we attempted to choose reaction conditions more efficiently for the degradation of sugarcane bagasse, a wet jet milling device together with L-cysteine as a reducing agent was used. As a result, we found that the degradation activity was almost twice as high with 10 mM L-cysteine compared with without it. These results will provide new insights for biomass utilization.

Mapping the deformability of natural and designed cellulosomes in solution

Background

Natural cellulosome multi-enzyme complexes, their components, and engineered ‘designer cellulosomes’ (DCs) promise an efficient means of breaking down cellulosic substrates into valuable biofuel products. Their broad uptake in biotechnology relies on boosting proximity-based synergy among the resident enzymes, but the modular architecture challenges structure determination and rational design.

Results

We used small angle X-ray scattering combined with molecular modeling to study the solution structure of cellulosomal components. These include three dockerin-bearing cellulases with distinct substrate specificities, original scaffoldins from the human gut bacterium Ruminococcus champanellensis (ScaA, ScaH and ScaK) and a trivalent cohesin-bearing designer scaffoldin (Scaf20L), followed by cellulosomal complexes comprising these components, and the nonavalent fully loaded Clostridium thermocellum CipA in complex with Cel8A from the same bacterium. The size analysis of R_g and D_max values deduced from the scattering curves and corresponding molecular models highlight their variable aspects, depending on composition, size and spatial organization of the objects in solution.

Conclusions

Our data quantifies variability of form and compactness of cellulosomal components in solution and confirms that this native plasticity may well be related to speciation with respect to the substrate that is targeted. By showing that scaffoldins or components display enhanced compactness compared to the free objects, we provide new routes to rationally enhance their stability and performance in their environment of action.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13068-022-02165-3.

Enzymatic Conversion of Mannan-Rich Plant Waste Biomass into Prebiotic Mannooligosaccharides

A growing demand in novel food products for well-being and preventative medicine has attracted global attention on nutraceutical prebiotics. Various plant agro-processes produce large amounts of residual biomass considered "wastes", which can potentially be used to produce nutraceutical prebiotics, such as manno-oligosaccharides (MOS). MOS can be produced from the degradation of mannan. Mannan has a main backbone consisting of β-1,4-linked mannose residues (which may be interspersed by glucose residues) with galactose substituents. Endo-β-1,4-mannanases cleave the mannan backbone at cleavage sites determined by the substitution pattern and thus give rise to different MOS products. These MOS products serve as prebiotics to stimulate various types of intestinal bacteria and cause them to produce fermentation products in different parts of the gastrointestinal tract which benefit the host. This article reviews recent advances in understanding the exploitation of plant residual biomass via the enzymatic production and characterization of MOS, and the influence of MOS on beneficial gut microbiota and their biological effects (i.e., immune modulation and lipidemic effects) as observed on human and animal health.

Combination of CTec2 and GH5 or GH26 Endo-Mannanases for Effective Lignocellulosic Biomass Degradation

Among endo-mannanases, glycoside hydrolase (GH) family 26 enzymes have been shown to be more catalytically active than GH5 enzymes on mannans. However, only GH5 endo-mannanases have been used for the formulation of enzyme cocktails. In this study, Bacillus sp.-derived GH5 and GH26 endo-mannanases were comparatively analysed biochemically for their synergistic action with a commercial cellulase blend, CTec2, during pre-treated lignocellulose degradation. Substrate specificity and thermo-stability studies on mannan substrates showed that GH26 endo-mannanase was more catalytically active and stable than GH5. GH26 also exhibited higher binding affinity for mannan than GH5, while GH5 showed more affinity for lignocellulosic substrates than GH26. Applying the endo-mannanases in combination with CTec2 for lignocellulose degradation led to synergism with a 1.3-fold increase in reducing sugar release compared to when CTec2 was used alone. This study showed that using the activity of endo-mannanases displayed with model substrates is a poor predictor of their activity and synergism on complex lignocelluloses.

Pretreatment of Lignocellulosic Materials as Substrates for Fermentation Processes

Lignocellulosic biomass is an abundant and renewable resource that potentially contains large amounts of energy. It is an interesting alternative for fossil fuels, allowing the production of biofuels and other organic compounds. In this paper, a review devoted to the processing of lignocellulosic materials as substrates for fermentation processes is presented. The review focuses on physical, chemical, physicochemical, enzymatic, and microbiologic methods of biomass pretreatment. In addition to the evaluation of the mentioned methods, the aim of the paper is to understand the possibilities of the biomass pretreatment and their influence on the efficiency of biofuels and organic compounds production. The effects of different pretreatment methods on the lignocellulosic biomass structure are described along with a discussion of the benefits and drawbacks of each method, including the potential generation of inhibitory compounds for enzymatic hydrolysis, the effect on cellulose digestibility, the generation of compounds that are toxic for the environment, and energy and economic demand. The results of the investigations imply that only the stepwise pretreatment procedure may ensure effective fermentation of the lignocellulosic biomass. Pretreatment step is still a challenge for obtaining cost-effective and competitive technology for large-scale conversion of lignocellulosic biomass into fermentable sugars with low inhibitory concentration.

Thin film of lignocellulosic nanofibrils with different chemical composition for QCM-D study

Thin films of lignocellulosic nanofibrils (LCNFs) with different chemical compositions were prepared for real-time observation of their enzymatic adsorption and degradation behavior by using a quartz crystal microbalance with dissipation monitoring (QCM-D). LCNFs were obtained by disk milling followed by high-pressure homogenization of Hinoki cypress. The lignin contents were adjusted by the sodium chlorite treatment. The film thickness was adjusted by controlling the concentration of the LCNF suspension, which was determined from its proportional relationship to the UV absorbance of lignin. The enzymatic degradation behavior was investigated with a commercial enzyme mixture. The results of the QCM-D showed that changes in frequency and dissipation in the initial reaction stage were different from the typical changes reported for pure cellulose. To the best of our knowledge, this is the first report of the preparation of thin films of LCNFs with high lignin and hemicellulose contents and their application in a QCM-D study.

A review of lignocellulose bioconversion using enzymatic hydrolysis and synergistic cooperation between enzymes--factors affecting enzymes, conversion and synergy

Lignocellulose is a complex substrate which requires a variety of enzymes, acting in synergy, for its complete hydrolysis. These synergistic interactions between different enzymes have been investigated in order to design optimal combinations and ratios of enzymes for different lignocellulosic substrates that have been subjected to different pretreatments. This review examines the enzymes required to degrade various components of lignocellulose and the impact of pretreatments on the lignocellulose components and the enzymes required for degradation. Many factors affect the enzymes and the optimisation of the hydrolysis process, such as enzyme ratios, substrate loadings, enzyme loadings, inhibitors, adsorption and surfactants. Consideration is also given to the calculation of degrees of synergy and yield. A model is further proposed for the optimisation of enzyme combinations based on a selection of individual or commercial enzyme mixtures. The main area for further study is the effect of and interaction between different hemicellulases on complex substrates.