Multienzymatic Cascades and Nanomaterial Scaffolding-A Potential Way Forward for the Efficient Biosynthesis of Novel Chemical Products

Synthetic biology is touted as the next industrial revolution as it promises access to greener biocatalytic syntheses to replace many industrial organic chemistries. Here, it is shown to what synthetic biology can offer in the form of multienzyme cascades for the synthesis of the most basic of new materials-chemicals, including especially designer chemical products and their analogs. Since achieving this is predicated on dramatically expanding the chemical space that enzymes access, such chemistry will probably be undertaken in cell-free or minimalist formats to overcome the inherent toxicity of non-natural substrates to living cells. Laying out relevant aspects that need to be considered in the design of multi-enzymatic cascades for these purposes is begun. Representative multienzymatic cascades are critically reviewed, which have been specifically developed for the synthesis of compounds that have either been made only by traditional organic synthesis along with those cascades utilized for novel compound syntheses. Lastly, an overview of strategies that look toward exploiting bio/nanomaterials for accessing channeling and other nanoscale materials phenomena in vitro to direct novel enzymatic biosynthesis and improve catalytic efficiency is provided. Finally, a perspective on what is needed for this field to develop in the short and long term is presented.

Nanotechnology based technological development in biofuel production: Current status and future prospects

Depleting fossil fuels and net carbon emissions associated with their burning have driven the need to find alternative energy sources. Biofuels are near-perfect candidates for alternative energy sources as they are renewable and account for no net CO2 emissions. However, biofuel production must overcome various challenges to compete with conventional fuels. Conventional methods for bioconversion of biomass to biofuel include chemical, thermochemical, and biological processes. Substrate selection and processing, low yield, and total cost of production are some of the main issues associated with biofuel generation. Recently, the uses of nanotechnology and nanoparticles have been explored to improve the biofuel production processes because of their high adsorption, high reactivity, and catalytic properties. The role of these nanoscale particles and nanocatalysts in biomass conversion and their effect on biofuel production processes and yield are discussed in the present article. The applicability of nanotechnology in production processes of biobutanol, bioethanol, biodiesel, biohydrogen, and biogas under biorefinery approach are presented. Different types of nanoparticles, and their function in the bioprocess, such as electron transfer, pretreatment, hydrolysis, microalgae cultivation, lipid extraction, dark and photo fermentation, immobilization, and suppression of inhibitory compounds, are also highlighted. Finally, the current and potential applications of nanotechnology in biorefineries are also discussed.

Industrial applications of immobilized nano-biocatalysts

Immobilized enzyme-based catalytic constructs could greatly improve various industrial processes due to their extraordinary catalytic activity and reaction specificity. In recent decades, nano-enzymes, defined as enzyme immobilized on nanomaterials, gained popularity for the enzymes' improved stability, reusability, and ease of separation from the biocatalytic process. Thus, enzymes can be strategically incorporated into nanostructured materials to engineer nano-enzymes, such as nanoporous particles, nanofibers, nanoflowers, nanogels, nanomembranes, metal-organic frameworks, multi-walled or single-walled carbon nanotubes, and nanoparticles with tuned shape and size. Surface-area-to-volume ratio, pore-volume, chemical compositions, electrical charge or conductivity of nanomaterials, protein charge, hydrophobicity, and amino acid composition on protein surface play fundamental roles in the nano-enzyme preparation and catalytic properties. With proper understanding, the optimization of the above-mentioned factors will lead to favorable micro-environments for biocatalysts of industrial relevance. Thus, the application of nano-enzymes promise to further strengthen the advances in catalysis, biotransformation, biosensing, and biomarker discovery. Herein, this review article spotlights recent progress in nano-enzyme development and their possible implementation in different areas, including biomedicine, biosensors, bioremediation of industrial pollutants, biofuel production, textile, leather, detergent, food industries and antifouling.

Recent nanobiotechnological advancements in lignocellulosic biomass valorization: A review

Increase in human population, rapid industrialization, excessive utilization of fossil fuel utilization and anthropogenic activities have caused serious threats to the environment in terms of greenhouse gas emissions (GHGs), global warming, air pollution, acid rain, etc. This destruction in sustainability can be averted by a paradigm shift in the fuel production from fossil resources to bioenergy. Amongst different forms of bioenergy, lignocellulosic biomass can be utilized as an attractive substrate for the production of several high-value products owing to its renewability, easy availability, and abundance. Additionally, utilization of these waste biomasses reduces the environmental hazards associated with its disposal. Impedance of lignin and crystalline nature of cellulose pose major bottlenecks in biomass based energy. Though, several physio-chemicals processes are recommended as mitigation route but none of them seems to be promising for large scale application. In recent years, a right fusion of biological treatment combined with nanotechnology for efficient pretreatment and subsequent hydrolysis of biomass by ubiquitous enzymes seems to be promising alternative. In addition, to overcome these difficulties, nanotechnology-based methods have been recently adopted in catalytic valorization of lignocellulosic biomass. The present review has critically discussed the application of nano-biotechnology in lignocellulosic biomass valorization in terms of pretreatment and hydrolysis. A detailed discussion on the application of various nanoparticles in these processes, enzyme immobilization and end-production utilization is presented in this review. Finally, the review emphasizes the major challenges of this process along with different routes and recommendations to address the issues.

Enzyme catalysis coupled with artificial membranes towards process intensification in biorefinery- a review

In this review, for the first time, the conjugation of the major types of enzymes used in biorefineries and the membrane processes to develop different configurations of MBRs, was analyzedfor the production of biofuels, phytotherapics and food ingredients. In particular, the aim is to critically review all the works related to the application of MBR in biorefinery, highlighting the advantages and the main drawbacks which can interfere with the development of this system at industrial scale. Alternatives strategies to overcome main limits will be also described in the different application fields, such as the use of biofunctionalized magnetic nanoparticles associated with membrane processes for enzyme re-use and membrane cleaning or the membrane fouling control by the use of integrated membrane process associated with MBR.

Cellulose-deconstruction potential of nano-biocatalytic systems: A strategic drive from designing to sustainable applications of immobilized cellulases

Nanostructured materials along with an added value of polymers-based support carriers have gained high interest and considered ideal for enzyme immobilization. The recently emerged nanoscience interface in the form of nanostructured materials combined with immobilized-enzyme-based bio-catalysis has now become research and development frontiers in advance and applied bio-catalysis engineering. With the involvement of nanoscience, various polymers have been thoroughly developed and exploited to nanostructured engineer constructs as ideal support carriers/matrices. Such nanotechnologically engineered support carriers/matrix possesses unique structural, physicochemical, and functional attributes which equilibrate principal factors and strengthen the biocatalysts efficacy for multipurpose applications. In addition, nano-supported catalysts are potential alternatives that can outstrip several limitations of conventional biocatalysts, such as reduced catalytic efficacy and turnover, low mass transfer efficiency, instability during the reaction, and most importantly, partial, or complete inhibition/deactivation. In this context, engineering robust and highly efficient biocatalysts is an industrially relevant prerequisite. This review comprehensively covered various biopolymers and nanostructured materials, including silica, hybrid nanoflower, nanotubes or nanofibers, nanomembranes, graphene oxide nanoparticles, metal-oxide frameworks, and magnetic nanoparticles as robust matrices for cellulase immobilization. The work is further enriched by spotlighting applied and industrially relevant considerations of nano-immobilized cellulases. For instance, owing to the cellulose-deconstruction features of nano-immobilized cellulases, the applications like lignocellulosic biomass conversion into industrially useful products or biofuels, improved paper sheet density and pulp beat in paper and pulp industry, fruit juice clarification in food industry are evident examples of cellulases, thereof are discussed in this work.

Simultaneous glucose production from cellulose and fouling reduction using a magnetic responsive membrane reactor with superparamagnetic nanoparticles carrying cellulolytic enzymes

This work aimed at investigating simultaneous hydrolysis of cellulose and in-situ foulant degradation in a cellulose fed superparamagnetic biocatalytic membrane reactor (BMR^SP). In this reactor, a dynamic layer of superparamagnetic bionanocomposites with immobilized cellulolytic enzymes were reversibly immobilized on superparamagnetic polymeric membrane using an external magnetic field. The formation of a dynamic layer of bionanocomposites on the membrane helped to prevent direct membrane-foulant interaction. Due to in-situ biocatalysis, there was limited filtration resistance. Simultaneous separation of the product helped to avoid enzyme product inhibition, achieve constant reaction rate over time and 50% higher enzyme efficiency than batch reactor. Stable enzyme immobilization and the ability to keep enzyme in the system for long period helped to achieve continuous productivity at very low enzyme but high solid loading, while also reducing the extent of membrane fouling. Hence, the BMR^SP paves a path for sustainable production of bioethanol from the cheaply available lignocellulose.

Using temperature-responsive zwitterionic surfactant to enhance the enzymatic hydrolysis of lignocelluloses and recover cellulase by cooling

Some zwitterionic surfactants exhibit upper critical solution temperature (UCST) in aqueous solutions. For the zwitterionic surfactant solution mixed with cellulase, when its temperature is below UCST, the cellulase can be recovered by coprecipitation with zwitterionic surfactant. In this work, 3-(Hexadecyldimethylammonio) propanesulfonate (SB3-16) was selected to enhance the enzymatic hydrolysis of lignocelluloses and recover the cellulase. After adding 2mmol/L of SB3-16, the enzymatic digestibility of eucalyptus pretreated by dilute acid (Eu-DA) and by sulfite (Eu-SPORL) increased from 27.9% and 35.1% to 72.6% and 89.7%, respectively. The results showed that SB3-16 could reduce the non-productive adsorption of cellulase on hydrophobic interface, while it did not significantly inhibit the activity of cellulase. For the solution contained 1wt% SB3-16 and 200mg protein/L CTec2 cellulase, 55.2% of protein could be recovered by cooling. The filter paper activity of the recovered cellulase was 1.93FPU/mg protein, which was 95.8% of its initial activity.

Engineering of a novel cellulose-adherent cellulolytic Saccharomyces cerevisiae for cellulosic biofuel production

Cellulosic biofuel is the subject of increasing attention. The main obstacle toward its economic feasibility is the recalcitrance of lignocellulose requiring large amount of enzyme to break. Several engineered yeast strains have been developed with cellulolytic activities to reduce the need for enzyme addition, but exhibiting limited effect. Here, we report the successful engineering of a cellulose-adherent Saccharomyces cerevisiae displaying four different synergistic cellulases on the cell surface. The cellulase-displaying yeast strain exhibited clear cell-to-cellulose adhesion and a "tearing" cellulose degradation pattern; the adhesion ability correlated with enhanced surface area and roughness of the target cellulose fibers, resulting in higher hydrolysis efficiency. The engineered yeast directly produced ethanol from rice straw despite a more than 40% decrease in the required enzyme dosage for high-density fermentation. Thus, improved cell-to-cellulose interactions provided a novel strategy for increasing cellulose hydrolysis, suggesting a mechanism for promoting the feasibility of cellulosic biofuel production.

Net-Immobilization of β-glucosidase on Nonwoven Fabrics to Lower the Cost of "Cellulosic Ethanol" and Increase Cellulose Conversions

The main limitation preventing the use of enzymatic cellulosic ethanol in industrial production is its higher cost which is mainly due to the elevated price of β-glucosidase (BG). Herein, we report on a simple strategy for the in-situ encapsulation of BG for repeated cellulosic ethanol production. In this strategy, BG was net-immobilized into a poly(ethylene glycol) (PEG) net-cloth layer on a PP nonwoven fabric by way of the visible light-induced surface controlled/living graft cross-linking polymerization. The visible light and mild reaction conditions could ensure the activity retention of BG during immobilization, while the non-swelling uniform net-mesh formed by living cross-linking polymerization could prevent the leakage of BG effectively (at the immobilization rate of more than 98.6% and the leakage rate of only 0.4%). When the BG-loaded fabric was used in combination with free cellulase (CEL), the results of the catalytic reaction demonstrated that these BG-loaded fabrics could not only give a 40% increase in cellulose conversions but also be reused for more than fifteen batches without losing the activity. These BG-loaded fabrics with characteristics including easy separation, excellent operation stability, a low cost of the polymeric matrix and a simple fabrication process are particularly interesting for a future bio-fuel production strategy.

Understanding How Nanoparticle Attachment Enhances Phosphotriesterase Kinetic Efficiency

As a specific example of the enhancement of enzymatic activity that can be induced by nanoparticles, we investigate the hydrolysis of the organophosphate paraoxon by phosphotriesterase (PTE) when the latter is displayed on semiconductor quantum dots (QDs). PTE conjugation to QDs underwent extensive characterization including structural simulations, electrophoretic mobility shift assays, and dynamic light scattering to confirm orientational and ratiometric control over enzyme display which appears to be necessary for enhancement. PTE hydrolytic activity was then examined when attached to ca. 4 and 9 nm diameter QDs in comparison to controls of freely diffusing enzyme alone. The results confirm that the activity of the QD conjugates significantly exceeded that of freely diffusing PTE in both initial rate (∼4-fold) and enzymatic efficiency (∼2-fold). To probe kinetic acceleration, various modified assays including those with increased temperature, presence of a competitive inhibitor, and increased viscosity were undertaken to measure the activation energy and dissociation rates. Cumulatively, the data indicate that the higher activity is due to an acceleration in enzyme-product dissociation that is presumably driven by the markedly different microenvironment of the PTE-QD bioconjugate's hydration layer. This report highlights how a specific change in an enzymatic mechanism can be both identified and directly linked to its enhanced activity when displayed on a nanoparticle. Moreover, the generality of the mechanism suggests that it could well be responsible for other examples of nanoparticle-enhanced catalysis.

Cellulase assisted synthesis of nano-silver and gold: Application as immobilization matrix for biocatalysis

In the present study, we report in vitro synthesis of silver and gold nanoparticles (NPs) using cellulase enzyme in a single step reaction. Synthesized nanoparticles were characterized by UV-VIS spectroscopy, Dynamic Light Spectroscopy (DLS), Transmission Electron Microscopy (TEM), Energy-dispersive X-ray Spectroscopy (EDX), X-ray Diffraction (XRD), Circular Dichroism (CD) and Fourier Transform Infrared Spectroscopy (FTIR). UV-visible studies shows absorption band at 415nm and 520nm for silver and gold NPs respectively due to surface plasmon resonance. Sizes of NPs as shown by TEM are 5-25nm for silver and 5-20nm for gold. XRD peaks confirmed about phase purity and crystallinity of silver and gold NPs. FTIR data shows presence of amide I peak on both the NPs. The cellulase assisted synthesized NPs were further exploited as immobilization matrix for cellulase enzyme. Thermal stability analysis reveals that the immobilized cellulase on synthesized NPs retained 77-80% activity as compared to free enzyme. While reusability data suggests immobilized cellulase can be efficiently used up to sixth cycles with minimum loss of enzyme activity. The secondary structural analysis of cellulase enzyme during the synthesis of NPs and also after immobilization of cellulase on these NPs was carried out by CD spectroscopy.

Effect of nickel-cobaltite nanoparticles on production and thermostability of cellulases from newly isolated thermotolerant Aspergillus fumigatus NS (class: Eurotiomycetes)

In the present study, effect of nickel-cobaltite (NiCo2O4) nanoparticles (NPs) was investigated on production and thermostability of the cellulase enzyme system using newly isolated thermotolerant Aspergillus fumigatus NS belonging to the class Euratiomycetes. The NiCo2O4 NPs were synthesized via hydrothermal method assisted by post-annealing treatment and characterized through X-ray diffraction (XRD) and transmission electron microscopy (TEM) techniques. In the absence of NPs in the growth medium, filter paper cellulase (FP) activity of 18 IU/gds was achieved after 96 h, whereas 40 % higher FP activity in 72 h was observed with the addition of 1 mM concentration of NPs in the growth medium. Maximum production of endoglucanase (211 IU/gds), β-glucosidase (301 IU/gds), and xylanase (803 IU/gds) was achieved after 72 h without NPs (control), while in the presence of 1 mM concentration of NPs, endoglucanase, β-glucosidase, and xylanase activity increased by about 49, 53, and 19.8 %, respectively, after 48 h of incubation, against control, indicating a substantial increase in cellulase productivity with the addition of NiCo2O4 NPs in the growth medium. Crude enzyme was thermally stable for 7 h at 80 °C in presence of NPs, as against 4 h at the same temperature for control samples. Significant increase in the activity and improved thermal stability of cellulases in the presence of the NiCo2O4 NPs holds potential for use of NiCo2O4 NPs during enzyme production as well as hydrolysis. From the standpoint of biofuel production, these results hold enormous significance.

Covalent immobilization of β-glucosidase on magnetic particles for lignocellulose hydrolysis

β-Glucosidase hydrolyzes cellobiose to glucose and is an important enzyme in the consortium used for hydrolysis of cellulosic and lignocellulosic feedstocks. In the present work, β-glucosidase was covalently immobilized on non-porous magnetic particles to enable re-use of the enzyme. It was found that particles activated with cyanuric chloride and polyglutaraldehyde gave the highest bead-related immobilized enzyme activity when tested with p-nitrophenyl-β-D-glucopyranoside (104.7 and 82.2 U/g particles, respectively). Furthermore, the purified β-glucosidase preparation from Megazyme gave higher bead-related enzyme activities compared to Novozym 188 (79.0 and 9.8 U/g particles, respectively). A significant improvement in thermal stability was observed for immobilized enzyme compared to free enzyme; after 5 h (at 65 °C), 36 % of activity remained for the former, while there was no activity in the latter. The performance and recyclability of immobilized β-glucosidase on more complex substrate (pretreated spruce) was also studied. It was shown that adding immobilized β-glucosidase (16 U/g dry matter) to free cellulases (8 FPU/g dry matter) increased the hydrolysis yield of pretreated spruce from ca. 44 % to ca. 65 %. In addition, it was possible to re-use the immobilized β-glucosidase in the spruce and retain activity for at least four cycles. The immobilized enzyme thus shows promise for lignocellulose hydrolysis.

Recyclable thermoresponsive polymer-cellulase bioconjugates for biomass depolymerization

Here we report the construction and characterization of a recoverable, thermoresponsive polymer-endoglucanase bioconjugate that matches the activity of unmodified enzymes on insoluble cellulose substrates. Two copolymers exhibiting a thermoresponsive lower critical solution temperature (LCST) were created through the copolymerization of an aminooxy-bearing methacrylamide with N-isopropylacrylamide (NIPAm) or N-isopropylmethacrylamide (NIPMa). The aminooxy group provided a handle through which the LCST was adjusted through small-molecule quenching. This allowed materials with LCSTs ranging from 20.9 to 60.5 °C to be readily obtained after polymerization. The thermostable endoglucanase EGPh from the hypothermophilic Pyrococcus horikoshii was transaminated with pyridoxal-5'-phosphate to produce a ketone-bearing protein, which was then site-selectively modified through oxime linkage with benzylalkoxyamine or 5 kDa-poly(ethylene glycol)-alkoxyamine. These modified proteins showed activity comparable to the controls when assayed on an insoluble cellulosic substrate. Two polymer bioconjugates were then constructed using transaminated EGPh and the aminooxy-bearing copolymers. After 12 h, both bioconjugates produced an equivalent amount of free reducing sugars as the unmodified control using insoluble cellulose as a substrate. The recycling ability of the NIPAm copolymer-EGPh conjugate was determined through three rounds of activity, maintaining over 60% activity after two cycles of reuse and affording significantly more soluble carbohydrates than unmodified enzyme alone. When assayed on acid-pretreated Miscanthus, this bioconjugate increased the amount of reducing sugars by 2.8-fold over three rounds of activity. The synthetic strategy of this bioconjugate allows the LCST of the material to be changed readily from a common stock of copolymer and the method of attachment is applicable to a variety of proteins, enabling the same approach to be amenable to thermophile-derived cellulases or to the separation of multiple species using polymers with different recovery temperatures.