Characterization of Cellobiohydrolases from Schizophyllum commune KMJ820

Mild Alkaline Pretreatment of Rice Straw as a Feedstock in Microbial Fuel Cells for Generation of Bioelectricity

The dependency on non-renewable fossil fuels as an energy source has drastically increased global temperatures. Their continuous use poses a great threat to the existing energy reserves. Therefore, the energy sector has taken a turn toward developing eco-friendly, sustainable energy generation by using sustainable lignocellulosic wastes, such as rice straw (RS). For lignocellulosic waste to be utilized as an efficient energy source, it needs to be broken down into less complex forms by pretreatment processes, such as alkaline pretreatment using NaOH. Varied NaOH concentrations (0.5%,1.0%,1.5%,2%) for alkaline pretreatment of RS were used for the holocellulose generation. Amongst the four NaOH concentrations tested, RS-1.5% exhibited higher holocellulose generation of 80.1%, whereas 0.5%, 1 5 and 2% pointed 71.9%, 73.8%, and 78.5% holocellulose generation, respectively. Further, microbial fuel cells (MFCs) were tested for voltage generation by utilizing holocellulose generated from untreated (RS-0%) and mildly alkaline pretreated RS (RS-1.5%) as a feedstock. The MFC voltage and maximum power generation using RS-0% were 194 mV and 167 mW/m2, respectively. With RS-1.5%, the voltage and maximum power generation were 556 mV and 583 mW/m2, respectively. The power density of RS-1.5% was three-fold higher than that of RS-0%. The increase in MFC power generation suggests that alkaline pretreatment plays a crucial role in enhancing the overall performance.

Anaerobic Digestion of Agri-Food Wastes for Generating Biofuels

Presently, fossil fuels are extensively employed as major sources of energy, and their uses are considered unsustainable due to emissions of obnoxious gases on the burning of fossil fuels, which can lead to severe environmental complications, including human health. To tackle these issues, various processes are developing to waste as a feed to generate eco-friendly fuels. The biological production of fuels is considered to be more beneficial than physicochemical methods due to their environmentally friendly nature, high rate of conversion at ambient physiological conditions, and less energy-intensive. Among various biofuels, hydrogen (H₂) is considered as a wonderful due to high calorific value and generate water molecule as end product on the burning. The H₂ production from biowaste is demonstrated, and agri-food waste can be potentially used as a feedstock due to their high biodegradability over lignocellulosic-based biomass. Still, the H₂ production is uneconomical from biowaste in fuel competing market because of low yields and increased capital and operational expenses. Anaerobic digestion is widely used for waste management and the generation of value-added products. This article is highlighting the valorization of agri-food waste to biofuels in single (H₂) and two-stage bioprocesses of H₂ and CH₄ production.

Photocatalytic TiO2/CdS/ZnS nanocomposite induces Bacillus subtilis cell death by disrupting its metabolism and membrane integrity

Titanium dioxide (TiO₂) is widely characterized for its application in clinical diagnostics, therapeutics, cosmetics, nutrition, and environment management. Despite enormous potential, its dependence on ultraviolet (UV) light for photocatalytic activity limits its commercialization. Accordingly in the present study, a photo catalytically superior ternary complex of TiO₂ with Cadmium sulfide/Zinc sulfide (CdS/ZnS) has been synthesized, as well as, characterized for photo-induced antimicrobial activity. The band gap of crystalline TiO₂/CdS/ZnS nanocomposite has been reduced (2.26 eV) and nanocomposite has shown the optimal photo-activation at 590 nm. TiO₂ nanocomposite has significant bactericidal activity in visible light (P < 0.01). Exposure of the TiO₂ nanocomposite affected the cellular metabolism by altering the 1681 metabolic features (P < 0.001) culminating in poor cellular survivability. Additionally, photo-induced reactive oxygen species generation through nanocomposite disrupts the microbial cellular structure. The present study synthesized photocatalytic nanocomposite as well as unveiled the holistic cellular effect of theTiO₂/CdS/ZnS nanocomposite. Additionally, the present study also indicated the potential application of TiO₂/CdS/ZnS nanocomposite for sustainable environment management, therapeutics, and various industries.

Supplementary Information

The online version contains supplementary material available at 10.1007/s12088-021-00973-z.

Recombinant cellobiohydrolase of Myceliophthora thermophila: characterization and applicability in cellulose saccharification

A codon optimized cellobiohydrolase (CBH) encoding synthetic gene of 1188 bp from a thermophilic mold Myceliophthora thermophila (MtCel6A) was cloned and heterologously expressed in Escherichia coli for the first time. In silico analysis suggested that MtCel6A is a GH6 CBH and belongs to CBHII family, which is structurally similar to Cel6A of Humicola insolens. The recombinant MtCel6A is expressed as active inclusion bodies, and the molecular mass of the purified enzyme is ~ 45 kDa. The rMtCel6A is active in a wide range of pH (4-12) and temperatures (40-100 °C) with optima at pH 10.0 and 60 °C. It exhibits T1/2 of 6.0 and 1.0 h at 60 and 90 °C, respectively. The rMtCel6A is an extremozyme with organic solvent, salt and alkali tolerance. The Km, Vmax, kcat and kcat/Km values of the enzyme are 3.2 mg mL-1, 222.2 μmol mg-1 min-1, 2492 s-1 and 778.7 s-1 mg-1 mL-1, respectively. The product analysis of rMtCel6A confirmed that it is an exoenzyme that acts from the non-reducing end of cellulose. The addition of rMtCel6A to the commercial cellulase mix (Cellic CTec2) led to 1.9-fold increase in saccharification of the pre-treated sugarcane bagasse. The rMtCel6A is a potential CBH that finds utility in industrial processes such as in bioethanol, paper pulp and textile industries.

Biotin and Zn2+ Increase Xylitol Production by Candida tropicalis

In this study, the medium requirements to increase the production of xylitol by using Candida tropicalis (CT) have been investigated. The technique of single addition or omission of medium components was applied to determine the nutritional requirements. The addition of amino acids such as Asp, Glu, Gln, Asn, Thr, and Gly had no significant effect on CT growth. However, in the absence of other metal ions, there was a higher concentration of cell growth and xylitol production when only Zn2+ was present in the medium. The analysis of various vitamins unveiled that biotin and thiamine were the only vitamins required for the growth of CT. Surprisingly, when only biotin was present in the medium as a vitamin, there was less growth of CT than when the medium was complete, but the amount of xylitol released was significantly higher. Overall, this study will increase the xylitol production using the single omission or addtion technique.

LPMO AfAA9_B and Cellobiohydrolase AfCel6A from A. fumigatus Boost Enzymatic Saccharification Activity of Cellulase Cocktail

Cellulose is the most abundant polysaccharide in lignocellulosic biomass, where it is interlinked with lignin and hemicellulose. Bioethanol can be produced from biomass. Since breaking down biomass is difficult, cellulose-active enzymes secreted by filamentous fungi play an important role in degrading recalcitrant lignocellulosic biomass. We characterized a cellobiohydrolase (AfCel6A) and lytic polysaccharide monooxygenase LPMO (AfAA9_B) from Aspergillus fumigatus after they were expressed in Pichia pastoris and purified. The biochemical parameters suggested that the enzymes were stable; the optimal temperature was ~60 °C. Further characterization revealed high turnover numbers (kcat of 147.9 s-1 and 0.64 s-1, respectively). Surprisingly, when combined, AfCel6A and AfAA9_B did not act synergistically. AfCel6A and AfAA9_B association inhibited AfCel6A activity, an outcome that needs to be further investigated. However, AfCel6A or AfAA9_B addition boosted the enzymatic saccharification activity of a cellulase cocktail and the activity of cellulase Af-EGL7. Enzymatic cocktail supplementation with AfCel6A or AfAA9_B boosted the yield of fermentable sugars from complex substrates, especially sugarcane exploded bagasse, by up to 95%. The synergism between the cellulase cocktail and AfAA9_B was enzyme- and substrate-specific, which suggests a specific enzymatic cocktail for each biomass by up to 95%. The synergism between the cellulase cocktail and AfAA9_B was enzyme- and substrate-specific, which suggests a specific enzymatic cocktail for each biomass.

Rhus vernicifera Laccase Immobilization on Magnetic Nanoparticles to Improve Stability and Its Potential Application in Bisphenol A Degradation

In the present study, Rhus vernicifera laccase (RvLac) was immobilized through covalent methods on the magnetic nanoparticles. Fe₂O₃ and Fe₃O₄ nanoparticles activated by 3-aminopropyltriethoxysilane followed with glutaraldehyde showed maximum immobilization yields and relative activity up to 81.4 and 84.3% at optimum incubation and pH of 18 h and 5.8, respectively. The maximum RvLac loading of 156 mg/g of support was recorded on Fe₂O₃ nanoparticles. A higher optimum pH and temperature of 4.0 and 45 °C were noted for immobilized enzyme compared to values of 3.5 and 40 °C for free form, respectively. Immobilized RvLac exhibited better relative activity profiles at various pH and temperature ranges. The immobilized enzyme showed up to 16-fold improvement in the thermal stability, when incubated at 60 °C, and retained up to 82.9% of residual activity after ten cycles of reuses. Immobilized RvLac exhibited up to 1.9-fold higher bisphenol A degradation efficiency potential over free enzyme. Previous reports have demonstrated the immobilization of RvLac on non-magnetic supports. This study has demonstrated that immobilization of RvLac on magnetic nanoparticles is very efficient especially for achieving high loading, better pH and temperature profiles, and thermal- and solvents-stability, high reusability, and higher degradation of bisphenol A.

Biomethanol Production from Methane by Immobilized Co-cultures of Methanotrophs

Methanol production by co-culture of methanotrophs Methylocystis bryophila and Methyloferula stellata was examined from methane, a greenhouse gas. Co-culture exhibited higher methanol yield of 4.72 mM at optimum ratio of M. bryophila and M. stellata (3:2) compared to individual cultures. The immobilized co-culture within polyvinyl alcohol (PVA) showed relative efficiency of 90.1% for methanol production at polymer concentration of 10% (v/v). The immobilized co-culture cells within PVA resulted in higher bioprocess stability over free cells at different pH, and temperatures. Free and encapsulated co-cultures showed maximum methanol production of 4.81 and 5.37 mM under optimum conditions, respectively. After five cycles of reusage under batch conditions, free and encapsulated co-cultures retained methanol production efficiency of 23.8 and 61.9%, respectively. The present investigation successfully revealed the useful influence of co-culture on the methanol production over pure culture. Further, encapsulation within the polymeric matrix proved to be a better approach for the enhanced stability of the bioprocess.