Carbonic anhydrase conjugated to nanosilver immobilized onto mesoporous SBA-15 for sequestration of CO2

Direct Biocatalytic Processes for CO2 Capture as a Green Tool to Produce Value-Added Chemicals

Direct biocatalytic processes for CO₂ capture and transformation in value-added chemicals may be considered a useful tool for reducing the concentration of this greenhouse gas in the atmosphere. Among the other enzymes, carbonic anhydrase (CA) and formate dehydrogenase (FDH) are two key biocatalysts suitable for this challenge, facilitating the uptake of carbon dioxide from the atmosphere in complementary ways. Carbonic anhydrases accelerate CO₂ uptake by promoting its solubility in water in the form of hydrogen carbonate as the first step in converting the gas into a species widely used in carbon capture storage and its utilization processes (CCSU), particularly in carbonation and mineralization methods. On the other hand, formate dehydrogenases represent the biocatalytic machinery evolved by certain organisms to convert CO₂ into enriched, reduced, and easily transportable hydrogen species, such as formic acid, via enzymatic cascade systems that obtain energy from chemical species, electrochemical sources, or light. Formic acid is the basis for fixing C₁-carbon species to other, more reduced molecules. In this review, the state-of-the-art of both methods of CO₂ uptake is assessed, highlighting the biotechnological approaches that have been developed using both enzymes.

Carbonic anhydrase as a tool to mitigate global warming

The global average temperature breaks the record every year, and this unprecedented speed at which it is unfolding is causing serious climate change which in turn impacts the lives of humans and other living organisms. Thus, it is imperative to take immediate action to limit global warming. Increased CO2 emission from the industrial sector that relies on fossil fuels is the major culprit. Mitigating global warming is an uphill battle that involves an integration of technologies such as switching to renewable energy, increasing the carbon sink capacity, and implementing carbon capture and sequestration (CCS) on major sources of CO2 emissions. Among all these methods, CCS is globally accepted as a potential technology to address this climate change. CCS using carbonic anhydrase (CA) is gaining momentum due to its advantages over other conventional CCS technologies. CA is a metalloenzyme that catalyses a fundamental reaction for life, i.e. the interconversion of bicarbonate and protons from carbon dioxide and water. The practical application of CA requires stable CAs operating under harsh operational conditions. CAs from extremophilic microbes are the potential candidates for the sequestration of CO2 and conversion into useful by-products. The soluble free form of CA is expensive, unstable, and non-reusable in an industrial setup. Immobilization of CA on various support materials can provide a better alternative for application in the sequestration of CO2. The present review provides insight into several types of CAs, their distinctive characteristics, sources, and recent developments in CA immobilization strategies for application in CO2 sequestration.

Strategies to improve the mass transfer in the CO2 capture process using immobilized carbonic anhydrase

High carbon dioxide (CO₂) concentration in the atmosphere urgently requires eco-friendly mitigation strategies. Carbonic anhydrase (CA) is a high-quality enzyme protein, available from a wide range of sources, which has an extremely high catalytic efficiency for the hydration of CO₂ compared with other catalytic CO₂ conversion systems. While free CA is costly and weakly stable, CA immobilization can significantly improve its stability and allow enzyme recycling. However, gaseous CO₂ is significantly different from traditional liquid substrates. Additionally, due to the presence of enzyme carriers, there is limited mass transfer between CO₂ and the active center of immobilized CA. Most of the available reviews provide an overview of the improvement in catalytic activity and stability of CA by different immobilization methods and substrates. However, they do not address the limited mass transfer between CO₂ and the active center of immobilized CA. Therefore, by focusing on the mass transfer process, this review presents CA immobilization strategies that are more efficient and of greater environmental tolerance by categorizing the methods of enhancing the mass transfer process at each stage of the enzymatic CO₂ capture reaction. Such improvements in this green and environmentally friendly biological carbon capture process can increase its efficiency for industrial applications.

Carbonic anhydrase to boost CO2 sequestration: Improving carbon capture utilization and storage (CCUS)

CO₂ Capture Utilization and Storage (CCUS) is a fundamental strategy to mitigate climate change, and carbon sequestration, through absorption, can be one of the solutions to achieving this goal. In nature, carbonic anhydrase (CA) catalyzes the CO₂ hydration to bicarbonates. Targeting the development of novel biotechnological routes which can compete with traditional CO₂ absorption methods, CA utilization has presented a potential to expand as a promising catalyst for CCUS applications. Driven by this feature, the search for novel CAs as biocatalysts and the utilization of enzyme improvement techniques, such as protein engineering and immobilization methods, has resulted in suitable variants able to catalyze CO₂ absorption at relevant industrial conditions. Limitations related to enzyme recovery and recyclability are still a concern in the field, affecting cost efficiency. Under different absorption approaches, CA enhances both kinetics and CO₂ absorption yields, besides reduced energy consumption. However, efforts directed to process optimization and demonstrative plants are still limited. A recent topic with great potential for development is the CA utilization in accelerated weathering, where industrial residues could be re-purposed towards becoming carbon sequestrating agents. Furthermore, research of new solvents has identified potential candidates for integration with CA in CO₂ capture, and through techno-economic assessments, CA can be a path to increase the competitiveness of alternative CO₂ absorption systems, offering lower environmental costs. This review provides a favorable scenario combining the enzyme and CO₂ capture, with possibilities in reaching an industrial-like stage in the future.

Immobilization of carbonic anhydrase for CO2 capture and utilization

Carbonic anhydrase (CA) is an excellent candidate for novel biocatalytic processes based on the capture and utilization of CO₂. The setup of efficient methods for enzyme immobilization makes CA utilization in continuous bioreactors increasingly attractive and opens up new opportunities for the industrial use of CA. The development of efficient processes for CO₂ capture and utilization (CCU) is one of the most challenging targets of modern chemical reaction engineering. In the general frame of CCU processes, the interest in the utilization of immobilized CA as a biocatalyst for augmentation of CO₂ reactive absorption has grown consistently over the last decade. The present mini-review surveys and discusses key methodologies for CA immobilization aimed at the development of heterogeneous biocatalysts for CCU. Advantages and drawbacks of covalent attachment on fine granular solids, immobilization as cross-linked enzyme aggregates, and "in vivo" immobilization methods are presented. In particular, criteria for optimal selection of CA-biocatalyst and design of CO₂ absorption units are presented and discussed to highlight the most effective solutions. Perspectives on biocatalytic CCU processes that can include the use of CA in an enzymatic reactive CO₂ absorption step are eventually presented with a special focus on two examples of CO₂ fixation pathways: hybrid enzyme-microalgae process and enzyme cascade for the production of carboxylic acids. KEY POINTS: • Covalent immobilization techniques applied to CA are effective for CO₂ ERA. • Biocatalyst type and morphology must be selected considering CO₂ ERA conditions. • Immobilized CA can offer novel routes to CO₂ capture and direct utilization.

Carbonic anhydrase modification for carbon management

Carbonic anhydrase modification (chemical and biological) is an attractive strategy for its diverse application to accelerate the absorption of CO₂ from a flue gas with improved activity and stability. This article reports various possibilities of CA modification using metal-ligand homologous chemistry, cross-linking agents, and residue- and group-specific and genetic modifications, and assesses their role in carbon management. Chemically modified carbonic anhydrase is able to improve the absorption of carbon dioxide from a gas stream into mediation compounds with enhanced sequestration and mineral formation. Genetically modified CA polypeptide can also increase carbon dioxide conversion. Chemical modification of CA can be categorized in terms of (i) residue-specific modification (involves protein-ligand interaction in terms of substitution/addition) and group-specific modifications (based on the functional groups of the target CA). For every sustainable change, there should be no/limited toxic or immunological response. In this review, several CA modification pathways and biocompatibility rules are proposed as a theoretical support for emerging research in this area.

Immobilization of carbonic anhydrase on polyvinylidene fluoride membranes

In recent years, the application of carbonic anhydrase (CA) in CO₂ removal has attracted great interest. However, obtaining high enzyme recovery activity is difficult in existing immobilization techniques. In this work, water plasma-treated poly(vinylidene fluoride) (PVDF) membranes were modified via 3-aminopropyl triethoxy silane (KH550) or γ-(2, 3-epoxypropoxy) propyl trimethoxy silane (KH560), and then CA was attached. The immobilization process was optimized, and the catalytic properties of PVDF-attached CA were characterized. The maximum activity recovery of PVDF-KH550-CA was 60%, whereas that of PVDF-KH560-CA was 33%. The K_m values of PVDF-KH550-CA, PVDF-KH560-CA, and free enzyme were 9.97 ± 0.37, 12.5 ± 0.2, and 6.18 ± 0.23 mM, respectively, and their K_cat /K_m values were 206 ± 2, 117 ± 5, and 488 ± 4 M^-1 ·Sec^-1 . PVDF-attached CA shows excellent storage stability and reusability, and their half-life values were 82 and 78 days at 4 °C. At 25 °C, they were 50 and 37 days, respectively. PVDF-KH550-CA and PVDF-KH560-CA retained approximately 85% and 72% of the initial activity after undergoing 10 cycles. In the presence of them, the generation rates of CaCO₃ were 76% and 65% of the free CA system, which were 1.6 and 1.3 times that of the blank system, respectively. Its role in accelerating CO₂ sequestration holds great promise for its practical application.

Co-production of carbonic anhydrase and phycobiliproteins by Spirulina sp. and Synechococcus nidulans

The aim of this work was to study the co-production of the carbonic anhydrase, C-phycocyanin and allophycocyanin during cyanobacteria growth. Spirulina sp. LEB 18 demonstrated a high potential for simultaneously obtaining the three products, achieving a carbonic anhydrase (CA) productivity of 0.97U/L/d and the highest C-phycocyanin (PC, 5.9μg/mL/d) and allophycocyanin (APC, 4.3μg/mL/d) productivities. In the extraction study, high extraction yields were obtained from Spirulina using an ultrasonic homogenizer (CA: 25.5U/g; PC: 90mg/g; APC: 70mg/g). From the same biomass, it was possible to obtain three biomolecules that present high industrial value.

Carbonic anhydrase mediated carbon dioxide sequestration: promises, challenges and future prospects

Anthropogenic activities have substantially increased the level of greenhouse gases (GHGs) in the atmosphere and are contributing significantly to the global warming. Carbon dioxide (CO2 ) is one of the major GHGs which plays a key role in the climate change. Various approaches and methodologies are under investigation to address CO2 capture and sequestration worldwide. Carbonic anhydrase (CA) mediated CO2 sequestration is one of the promising options. Therefore, the present review elaborates recent developments in CA, its immobilization and bioreactor methodologies towards CO2 sequestration using the CA enzyme. The promises and challenges associated with the efficient utilization of CA for CO2 sequestration and scale up from flask to lab-scale bioreactor are critically discussed. Finally, the current review also recommends the possible future needs and directions to utilize CA for CO2 sequestration.

Enzymatic Carbon Dioxide Capture

In the past decade, the capture of anthropic carbonic dioxide and its storage or transformation have emerged as major tasks to achieve, in order to control the increasing atmospheric temperature of our planet. One possibility rests on the use of carbonic anhydrase enzymes, which have been long known to accelerate the hydration of neutral aqueous CO2 molecules to ionic bicarbonate species. In this paper, the principle underlying the use of these enzymes is summarized. Their main characteristics, including their structure and catalysis kinetics, are presented. A special section is next devoted to the main types of CO2 capture reactors under development, to possibly use these enzymes industrially. Finally, the possible application of carbonic anhydrases to directly store the captured CO2 as inert solid carbonates deserves a review presented in a final section.

Expression and characterization of codon-optimized carbonic anhydrase from Dunaliella species for CO(2) sequestration application

Carbonic anhydrases (CAs) have been given much attention as biocatalysts for CO(2) sequestration process because of their ability to convert CO(2) to bicarbonate. Here, we expressed codon-optimized sequence of α-type CA cloned from Dunaliella species (Dsp-aCAopt) and characterized its catalyzing properties to apply for CO(2) to calcite formation. The expressed amount of Dsp-aCAopt in Escherichia coli is about 50 mg/L via induction of 1.0 mM isopropyl-β-D-thiogalactopyranoside at 20 °C (for the case of intact Dsp-aCA, negligible). Dsp-aCAopt enzyme shows 47 °C of half-denaturation temperature and show wide pH stability (optimum pH 7.6/10.0). Apparent values of K (m) and V (max) for p-nitrophenylacetate substrate are 0.91 mM and 3.303 × 10(-5) μM min(-1). The effects of metal ions and anions were investigated to find out which factors enhance or inhibit Dsp-aCAopt activity. Finally, we demonstrated that Dsp-aCAopt enzyme can catalyze well the conversion of CO(2) to CaCO(3), as the calcite form, in the Ca(2+) solution [8.9 mg/100 μg (172 U/mg enzyme) with 10 mM of Ca(2+)]. The obtained expression and characterization results of Dsp-aCAopt would be usefully employed for the development of efficient CA-based system for CO(2)-converting/capturing processes.