Enhanced biomimetic sequestration of CO2 into CaCO3 using purified carbonic anhydrase from indigenous bacterial strains

Bacterial carbonic anhydrase-induced carbonates mitigate soil erosion in biological soil crusts

Soil erosion is a significant environmental issue worldwide, particularly in island regions where land resources are exceedingly scarce. Biological soil crusts play a crucial role in mitigating soil erosion, yet the precise effect and mechanism of biological soil crusts against erosion remain ambiguous. In this study, biological soil crusts at various developmental stages from a tropical coral island in the South China Sea were chosen to investigate the role of carbonic anhydrase in mitigating erosion. A cohesive strength meter, real-time quantitative PCR, and 16S rRNA gene high-throughput sequencing were employed to assess variations in soil antiscouribility as well as bacterial abundance and composition during the formation and development of biological soil crusts. Scanning electron microscopy was utilized to detect carbonates induced by bacterial carbonic anhydrase and elucidate their role in the solidification of sand particles. The findings indicate that the formation and development of biological soil crusts significantly enhance anti-scouribility. Comparison to those of bare coral sand, the shear stress increased from 0.35 to 1.11 N/m2 in the dark biocrusts. Moreover, significantly elevated carbonic anhydrase activity was observed in biological soil crusts, demonstrating a positive correlation with antiscouribility. In addition, there was a significant increase in bacterial abundance within the biological soil crusts. The enrichment of Cyanobacteriales and Chloroflexales potentially contributed to the increased carbonic anhydrase activity and antiscouribility. Furthermore, three cyanobacterial strains with carbonic anhydrase activity were isolated from biological soil crusts and subsequently confirmed to enhance sand solidification through microbial carbonate precipitation. This study presents initial evidence for the role of microbial carbonic anhydrase in enhancing the antiscouribility of biological soil crusts during their formation and development. These findings offer novel insights into the functional and mechanistic dimensions underlying the mitigation of soil erosion facilitated by biological soil crusts, which are valuable for implementing sustainable biorestoration and environmental management technologies to prevent soil erosion.

Effect of Clay Minerals on Carbonate Precipitation Induced by Cyanobacterium Synechococcus sp

Carbonate precipitation induced by cyanobacteria is an important factor in lacustrine fine-grained carbonate rock genesis. As key components of these rocks, clay minerals play an important role in aggregating cyanobacteria. However, the formation mechanism of fine-grained carbonate under the effect of clay minerals is unclear. In this study, we investigated carbonate precipitation by Synechococcus cells under the influence of clay minerals. The results showed that clay minerals can accelerate Synechococcus aggregation, and the aggregation rate of the kaolinite group was significantly higher than that of montmorillonite. The aggregate size and Synechococcus cell content increased with an increase in clay minerals, resulting in increasing organic matter and carboxyl content in the aggregates. Due to the high affinity between carboxyl and Ca2+, the presence of Synechococcus sp. could improve the Mg/Ca molar ratio in the microenvironment of aggregates, which is conducive to aragonite precipitation. Thus, aragonite 5 to 10 μm in size precipitated when Synechococcus and clay minerals coexisted, whereas low-magnesium calcite (15 to 60 μm) was the main carbonate only in the presence of Synechococcus. This study provides important insights into the mechanisms of microbial-induced carbonate precipitation under the effect of clay minerals, which might offer theoretical support for the genesis of fine-grained lacustrine carbonate. IMPORTANCE The biogenesis of lacustrine fine-grained carbonates is of great significance to the exploitation of shale oil. Clay minerals are an important component of lacustrine fine-grained sedimentary rocks, which is conductive to the aggregation and settlement of cyanobacteria. We investigated the precipitation of carbonate induced by Synechococcus sp. with the addition of kaolinite and montmorillonite. The pH and calcium carbonate saturation of the environment increased under the effect of cyanobacteria photosynthesis. The aggregation of cyanobacteria cells increased the Mg/Ca molar ratio of the microenvironment, creating a favorable condition for the precipitation of aragonite, which was similar in size to the micritic calcite of fine-grained sedimentary rocks. This study provides theoretical support for the genesis of fine-grained carbonates.

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.

Biosequestration of carbon dioxide using carbonic anhydrase from novel Streptomyces kunmingensis

The increase in the atmospheric concentrations of carbon dioxide due to anthropogenic interventions has led to several undesirable consequences, notably global warming and related changes. Avoidance of and/or removal of carbon dioxide will result in the reduction of global warming. Biosequestration of carbon by using carbonic anhydrase (CA) as biocatalyst is one of most effective approaches. In the present study, actinobacterial cultures isolated from bamboo (Bambusa vulgaris) rhizosphere were screened for the production of carbonic anhydrase enzyme. The strain BS19 which showed promising CA production was selected as the potential strain. Strain BS19 was identified as Streptomyces kunmingensis based on the phenotypic and molecular characteristics. In submerged fermentation, strain BS19 produced 214.21 IU/ml of CA enzyme. The molecular mass of the CA was determined as 45 ± 2 kDa. The production of CA was found to be optimal at pH 7.0 and at temperature of 28 °C. The full length periplasmic CA gene was successfully amplified from S. kunmingensis BS19. Biomimetic sequestration of carbon was detected and quantified through CaCO₃ precipitation method. Further, the CA of BS 19 was successfully used to mineralize CO₂ present in motorbike exhaust, which has a similar composition to that of flue gas. The well-defined rhombohedral calcite crystals formed in the mineral carbonation reaction was observed through SEM analysis. The findings of this study clearly indicated that Streptomyces kunmingensis BS19 isolated from bamboo rhizosphere is a promising candidate for the production of carbonic anhydrase which deserves the potential for CO₂ sequestration.

A Review on the Performance Evaluation of Autonomous Self-Healing Bacterial Concrete: Mechanisms, Strength, Durability, and Microstructural Properties

The development of cracks, owing to a relatively lower tensile strength of concrete, diverse loading, and environmental factors driving the deterioration of structures, is an inescapable key concern for engineers. Reparation and maintenance operations are thus extremely important to prevent cracks from spreading and mitigating the lifetime of structures. However, ease of access to the cracked zone may be challenging, and it also needs funds and manual power. Hence, autonomous sealing of cracks employing microorganisms into the concrete sans manual intervention is a promising solution to the dilemma of the sustainable improvement of concrete. ‘Ureolytic bacteria’, key organism species in rumen-producing ‘urease’ enzymes such as Bacillus pasteurii or subtilis—when induced—are capable of producing calcium carbonate precipitations into the concrete. As their cell wall is anionic, CaCO3 accumulation on their surface is extensive, and the whole cell, therefore, becomes crystalline and ultimately plugs pores and cracks. This natural induction technique is an environmentally friendly method that researchers are studying intensively. This manuscript reviews the application process of bacterial healing to manufacture autonomous self-healing bacterial concrete. Additionally, it provides a brief review of diverse attributes of this novel concrete which demonstrate the variations with the auto-addition of different bacteria, along with an evaluation of crack healing as a result of the addition of these bacteria directly into concrete or after encapsulation in a protective shell. Comparative assessment techniques for autonomous, bio-based self-healing are also discussed, accompanied by progress, potential, modes of application of this technique, and its resultant benefits in the context of strength and durability. Imperatives for quantitative sustainability assessment and industrial adoption are identified, along with the sealing of artificially cracked cement mortar with sand as a filling material in given spaces, as well as urea and CaCl2 medium treatment with Bacillus pasteurii and Sporosarcina bacteria. The assessment of the impact on the compressive strength and rigidity of cement mortar cubes after the addition of bacteria into the mix is also considered. Scanning electron microscope (SEM) images on the function of bacteria in mineral precipitation that is microbiologically induced are also reviewed. Lastly, future research scope and present gaps are recognised and discussed.

Pharmacoscintigraphic evaluation and antidiabetic efficacy of gliclazide-loaded 99mTc-labelled mucoadhesive microspheres

Background

The current study was carried out to evaluate the possible application of Musa balbisiana starch in formulation of mucoadhesive microsphere for oral delivery of gliclazide (GLZ). The study objective was to improve the oral bioavailability along with prolongation of its duration of action for a better glycaemic control. Ionic gelation technique was employed in formulating the dosage form. Optimization of the batches was carried out by response surface methodology using 32 full factorial designs. The microsphere prepared was characterized for several parameters along with its in vitro release study. The gastrointestinal transit of the optimized batch of prepared microspheres after oral administration was studied in rabbits by using the gamma scintigraphy technique utilizing 99mTc as the labelling agent in the presence of stannous chloride. Also, the optimized batch was studied for its pharmacokinetic parameters. Moreover, the antidiabetic efficacy of the prepared microsphere was evaluated in rats by using the streptozotocin (STZ)-induced diabetic model.

Results

The factorial design experiment resulted in an optimum formulation coded as F8. The compatible nature of the drug and excipient was revealed from FTIR, DSC and IST studies. The scanning electron micrographs also showed the occurrence of spherical microspheres having a smooth surface. The in vitro release study provided an evidence of an initial burst effect that was followed by a prolong release phase. The pharmacokinetic parameters justified the ability of the prepared dosage form in sustaining the drug release with a 2.7-fold enhancement in drug bioavailability. The images obtained during the gamma scintigraphy study suggested the gastro-retentive nature of the dosage form with the gastro-retentive ability for more than 4 h. Also, the pharmacodynamics study carried out in diabetic rat model confirmed about the better efficacy of the dosage form in lowering the elevated blood glucose level.

Conclusion

The overall study data provide valuable information about the potential of this banana starch in formulation of a mucoadhesive dosage form that can be used for enhancement of bioavailability of drug-like gliclazide which in turn can provide a beneficial effect in the management of diabetes.

Selective Adsorption of Amino Acids in Crystals of Monohydrocalcite Induced by the Facultative Anaerobic Enterobacter ludwigii SYB1

The morphology, crystal structure, and elemental composition of biominerals are commonly different from chemically synthesized minerals, but the reasons for these are not fully understood. A facultative anaerobic bacterium, Enterobacter ludwigii SYB1, is used in experiments to document the hydrochemistry, mineral crystallization, and cell surface characteristics of biomineralization. It was found that carbonate anhydrase and ammonia production were major factors influencing the alkalinity and saturation of the closed biosystem. X-ray diffraction (XRD) spectra showed that calcite, monohydrocalcite (MHC), and dypingite formed in samples with bacterial cells. It was also found that the (222) plane of MHC was the preferred orientation compared to standard data. Scanning transmission electron microscopy (STEM) analysis of cell slices provides direct evidence of concentrated calcium and magnesium ions on the surface of extracellular polymeric substances (EPS). In addition, high-resolution transmission electron microscopy (HRTEM) showed that crystallized nanoparticles were formed within the EPS. Thus, the mechanism of the biomineralization induced by E. ludwigii SYB1 can be divided into three stages: (i) the production of carbonate anhydrase and ammonia increases the alkalinity and saturation state of the milieu, (ii) free calcium and magnesium ions are adsorbed and chelated onto EPS, and (iii) nanominerals crystallize and grow within the EPS. Seventeen kinds of amino acids were identified within both biotic MHC and the EPS of SYB1, while the percentages of glutamic and aspartic acid in MHC increased significantly (p < 0.05). Furthermore, the adsorption energy was calculated for various amino acids on seven diffracted crystal faces, with preferential adsorption demonstrated on (111) and (222) faces. At the same time, the lowest adsorption energy was always that of glutamic and aspartic acid for the same crystal plane. These results suggest that aspartic and glutamic acid always mix preferentially in the crystal lattice of MHC and that differential adsorption of amino acids on crystal planes can lead to their preferred orientation. Moreover, the mixing of amino acids in the mineral structure may also have a certain influence on the mineral lattice dislocations, thus enhancing the thermodynamic characteristics.

Bacteria incorporated with calcium lactate pentahydrate to improve the mortar properties and self-healing occurrence

Concrete can be harmful to the environment due to its high energy consumption and CO₂ emission and also has a potential crack formation, which can promote a drop in its strength. Therefore, concrete is considered as a non-sustainable material. The mechanisms by which bacterial oxidation of organic carbon can precipitate calcite that may fill the voids and cracks on cement-based materials have been extensively investigated to prevent and heal the micro-cracks formation. Hence, this study focused on utilizing a new alkaliphilic bacterial strain indigenous to an Indonesian site, Lysinibacillus sphaericus strain SKC/VA-1, incorporated with calcium lactate pentahydrate, as a low-cost calcium source, with various bacterial inoculum concentrations. The bacterium was employed in this study due to its ability to adapt to basic pH, thus improving the physical properties and rejuvenating the micro-cracks. Experimentally, the addition of calcium lactate pentahydrate slightly affected the mortar properties. Likewise, bacteria-incorporated mortar exhibited an enhancement in the physical properties of mortar. The highest improvement of mechanical properties (an increase of 45% and 36% for compressive and indirect tensile strength, respectively) was achieved by the addition of calcium lactate pentahydrate incorporated with 10% v/v bacterial inoculum [about 7 × 10⁷ CFU/ml (colony-forming unit/ml)]. The self-healing took place more rapidly on bacterial mortar supplemented with calcium lactate pentahydrate than on the control specimen. XRD analysis demonstrated that the mineralogical composition of self-healing precipitates was primarily dominated by calcite (CaCO₃), indicating the capacity of L. sphaericus strain SKC/VA-1 to precipitate calcite through organic carbon oxidation for self-healing the artificial crack on the mortar. To our knowledge, this is the first report on the potential utilization of the bacterium L. sphaericus incorporated with calcium lactate pentahydrate to increase the mortar properties, including its self-healing ability. However, further study with the water-cement ratio variation is required to investigate the possibility of using L. sphaericus and calcium lactate pentahydrate as an alternative method rather than reducing the water-cement ratio to enhance the mortar properties.

Microbially induced calcium carbonate precipitation: a widespread phenomenon in the biological world

Biodeposition of minerals is a widespread phenomenon in the biological world and is mediated by bacteria, fungi, protists, and plants. Calcium carbonate is one of those minerals that naturally precipitate as a by-product of microbial metabolic activities. Over recent years, microbially induced calcium carbonate precipitation (MICP) has been proposed as a potent solution to address many environmental and engineering issues. However, for being a viable alternative to conventional techniques as well as being financially and industrially competitive, various challenges need to be overcome. In this review, the detailed metabolic pathways, including ammonification of amino acids, dissimilatory reduction of nitrate, and urea degradation (ureolysis), along with the potent bacteria and the favorable conditions for precipitation of calcium carbonate, are explained. Moreover, this review highlights the potential environmental and engineering applications of MICP, including restoration of stones and concrete, improvement of soil properties, sand consolidation, bioremediation of contaminants, and carbon dioxide sequestration. The key research and development questions necessary for near future large-scale applications of this innovative technology are also discussed.

Cloning, Expression and Characterization of Two Beta Carbonic Anhydrases from a Newly Isolated CO2 Fixer, Serratia marcescens Wy064

Bacterial strains from karst landform soil were enriched via chemostat culture in the presence of sodium bicarbonate. Two chemolithotrophic strains were isolated and identified as Serratia marcescens Wy064 and Bacillus sp. Wy065. Both strains could grow using sodium bicarbonate as the sole carbon source. Furthermore, the supplement of the medium with three electron donors (Na₂S, NaNO₂, and Na₂S₂O₃) improved the growth of both strains. The activities of carbonic anhydrase (CA) and ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBisCO) could be detected in the crude enzyme of strain Wy064, implying that the strain Wy064 might employ Calvin cycle to fix CO₂. S. marcescens genome mining revealed four potential CA genes designated CA1-CA4. The proteins encoded by genes CA1-3 were cloned and expressed in Escherichia coli. The purified recombinant enzymes of CA1 and CA3 exhibited CO₂ hydration activities, whereas enzyme CA2 was expressed in inclusion bodies. A CO₂ hydration assay demonstrated that the specific activity of CA3 was significantly higher than that of CA1. The maximum CO₂ hydration activities for CA1 and CA3 were observed at pH 7.5 and 40 °C. The activities of CA1 and CA3 were significantly enhanced by several metal ions, especially Zn²⁺, which resulted in 21.1-fold and 26.1-fold increases of CO₂ hydration activities, respectively. The apparent K _m and V _max for CO₂ as substrate were 27 mM and 179 WAU/mg for CA1, and 14 mM and 247 WAU/mg for CA3, respectively. Structure modeling combined with sequence analysis indicated that CA1 and CA3 should belong to the Type II β-CA.

Thermo-alkali-stable α-carbonic anhydrase of Bacillus halodurans: heterologous expression in Pichia pastoris and applicability in carbon sequestration

Recombinant α-carbonic anhydrase of the polyextremophilic bacterium Bacillus halodurans TSLV1 (rBhCA) has been produced extracellularly in active form in Pichia pastoris under methanol inducible (AOX1) as well as constitutive (GAP) promoters. A marked improvement in rBhCA production was achieved by developing a P. pastoris recombinant that produces rBhCA constitutively as compared to that under inducible promoter. The purified rBhCA from P. pastoris is a glycosylated protein that displays a higher molecular mass (79.5 kDa) than that produced from E. coli recombinant (75 kDa); the former has a Tm of 75 °C, which is slightly higher than that of the latter (72 °C). The former rBhCA exhibits higher thermostability than the latter. The former sequestered CO₂ efficiently similar to that of the native BhCA and the latter. This is the first report on the production of recombinant carbonic anhydrase extracellularly in P. pastoris.

Trends, application and future prospectives of microbial carbonic anhydrase mediated carbonation process for CCUS

Growing industrialization and the desire for a better economy in countries has accelerated the emission of greenhouse gases (GHGs), by more than the buffering capacity of the earth's atmosphere. Among the various GHGs, carbon dioxide occupies the first position in the anthroposphere and has detrimental effects on the ecosystem. For decarbonization, several non-biological methods of carbon capture, utilization and storage (CCUS) have been in use for the past few decades, but they are suffering from narrow applicability. Recently, CO₂ emission and its disposal related problems have encouraged the implementation of bioprocessing to achieve a zero waste economy for a sustainable environment. Microbial carbonic anhydrase (CA) catalyses reversible CO₂ hydration and forms metal carbonates that mimic the natural phenomenon of weathering/carbonation and is gaining merit for CCUS. Thus, the diversity and specificity of CAs from different micro-organisms could be explored for CCUS. In the literature, more than 50 different microbial CAs have been explored for mineral carbonation. Further, microbial CAs can be engineered for the mineral carbonation process to develop new technology. CA driven carbonation is encouraging due to its large storage capacity and favourable chemistry, allowing site-specific sequestration and reusable product formation for other industries. Moreover, carbonation based CCUS holds five-fold more sequestration capacity over the next 100 years. Thus, it is an eco-friendly, feasible, viable option and believed to be the impending technology for CCUS. Here, we attempt to examine the distribution of various types of microbial CAs with their potential applications and future direction for carbon capture. Although there are few key challenges in bio-based technology, they need to be addressed in order to commercialize the technology.

Bacterial Community Dynamics and Biocement Formation during Stimulation and Augmentation: Implications for Soil Consolidation

Microbially-induced CaCO₃ precipitation (MICP) is a naturally occurring process wherein durable carbonates are formed as a result of microbial metabolic activities. In recent years, MICP technology has been widely harnessed for applications in civil engineering wherein synthesis of calcium carbonate crystals occurs at ambient temperature paving way for low energy biocement. MICP using pure urease (UA) and carbonic anhydrase (CA) producing bacteria has been promising in laboratory conditions. In the current study we enriched ureolytic and carbonic anhydrase communities in calcareous soil under biostimulation and bioaugmentation conditions and investigated the effect of microbial dynamics on carbonate precipitation, calcium carbonate polymorph selection and consolidation of biological sand column under nutrient limited and rich conditions. All treatments for stimulation and augmentation led to significant changes in the composition of indigenous bacterial population. Biostimulation as well as augmentation through the UA route was found to be faster and more effective compared to the CA route in terms of extracellular enzyme production and carbonate precipitation. Synergistic role of augmented cultures along with indigenous communities was recorded via both the routes of UA and CA as more effective calcification was seen in case of augmentation compared to stimulation. The survival of supplemented isolates in presence of indigenous bacterial communities was confirmed through sequencing of total diversity and it was seen that both UA and CA isolate had the potential to survive along with native communities under high nutrient conditions. Nutrient conditions played significant role in determining calcium carbonate polymorph fate as calcitic crystals dominated under high carbon supplementation. Finally, the consolidation of sand columns via stimulation and augmentation was successfully achieved through both UA and CA route under high nutrient conditions but higher consolidation in short time period was noticed in UA route. The study reports that based upon the organic carbon content in native soils, stimulation can be favored at sites with high organic carbon content while augmentation with repeated injections of nutrients can be applied on poor nutrient soils via different enrichment routes of microbial metabolism.

Utility of thermo-alkali-stable γ-CA from polyextremophilic bacterium Aeribacillus pallidus TSHB1 in biomimetic sequestration of CO2 and as a virtual peroxidase

Aeribacillus pallidus TSHB1 polyextremophilic bacterium produces a γ-carbonic anhydrase (ApCA), which is a homotrimeric biocatalyst with a subunit molecular mass of 32 ± 2 kDa. The enzyme is stable in the pH range between 8.0 and 11.0 and thus alkali-stable and moderately thermostable with T_1/2 values of 40 ± 1, 15 ± 1, and 8 ± 0.5 min at 60, 70, and 80 °C, respectively. Activation energy for irreversible inactivation "E _d " of carbonic anhydrase is 67.119 kJ mol^-1. The enzyme is stable in the presence of various flue gas contaminants such as SO₃^2-,SO₄^2-, and NO₃^- and cations Mg²⁺, Mn²⁺, Ca²⁺, and Ba²⁺. Fluorescence studies in the presence of N-bromosuccinimide and fluorescence quenching using KI and acrylamide revealed the importance of tryptophan residues in maintaining the structural integrity of the enzyme. ApCA is more efficient than the commercially available bovine carbonic anhydrase (BCA) in CO₂ sequestration. The enzyme was successfully used in biomineralization of CO₂ from flue gas. Replacement of active site Zn²⁺ with Mn²⁺ enabled ApCA to function as a peroxidase which exhibited alkali-stability and moderate thermostability like ApCA.

Expression and characterization of a codon-optimized alkaline-stable carbonic anhydrase from Aliivibrio salmonicida for CO2 sequestration applications

The CO₂ mineralization process, accelerated by carbonic anhydrase (CA) was proposed for the efficient capture and storage of CO₂, the accumulation of which in the atmosphere is the main cause of global warming. Here, we characterize a highly stable form of the cloned CA from the Gram-negative marine bacterium Aliivibrio salmonicida, named ASCA that can promote CO₂ absorption in an alkaline solvent required for efficient carbon capture. We designed a mature form of ASCA (mASCA) using a codon optimization of ASCA gene and removal of ASCA signal peptide. mASCA was highly expressed (255 mg/L) with a molecular weight of approximately 26 kDa. The mASCA enzyme exhibited stable esterase activity within a temperature range of 10-60 °C and a pH range of 6-11. mASCA activity remained stable for 48 h at pH 10. We also investigated its inhibition profiles using inorganic anions, such as acetazolamide, sulfanilamide, iodide, nitrate, and azide. We also demonstrate that mASCA is capable of catalyzing the conversion of CO₂ to CaCO₃ (calcite form) in the presence of Ca²⁺. It should be noted that mASCA enzyme exhibits high production yield and sufficient stabilities against relatively high temperature and alkaline pH, which are required conditions for the development of more efficient enzymatic CCS systems.

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.

Novel alkalistable α-carbonic anhydrase from the polyextremophilic bacterium Bacillus halodurans: characteristics and applicability in flue gas CO2 sequestration

The emissions of CO2 into the atmosphere have been constantly rising due to anthropogenic activities, which have led to global warming and climate change. Among various methods proposed for mitigating CO2 levels in the atmosphere, carbonic anhydrase (CA)-mediated carbon sequestration represents a greener and safer approach to capture and convert it into stable mineral carbonates. Despite the fact that CA is an extremely efficient metalloenzyme that catalyzes the hydration of CO2 (CO2 + H2O ↔ HCO3 (-) + H(+)) with a kcat of ∼10(6) s(-1), a thermostable, and alkalistable CA is desirable for the process to take place efficiently. The purified CA from alkaliphilic, moderately thermophilic, and halotolerant Bacillus halodurans TSLV1 (BhCA) is a homodimeric enzyme with a subunit molecular mass of ~37 kDa with stability in a broad pH range between 6.0 and 11.0. It has a moderate thermostability with a T1/2 of 24.0 ± 1.0 min at 60 °C. Based on the sensitivity of CA to specific inhibitors, BhCA is an α-CA; this has been confirmed by nucleotide/amino acid sequence analysis. This has a unique property of stimulation by SO4 (2-), and it remains unaffected by SO3 (2-), NOx, and most other components present in the flue gas. BhCA is highly efficient in accelerating the mineralization of CO2 as compared to commercial bovine carbonic anhydrase (BCA) and is also efficient in the sequestration of CO2 from the exhaust of petrol driven car, thus, a useful biocatalyst for sequestering CO2 from flue gas.

Accelerating Mineral Carbonation Using Carbonic Anhydrase

Carbonic anhydrase (CA) enzymes have gained considerable attention for their potential use in carbon dioxide (CO2) capture technologies because they are able to catalyze rapidly the interconversion of aqueous CO2 and bicarbonate. However, there are challenges for widespread implementation including the need to develop mineralization process routes for permanent carbon storage. Mineral carbonation of highly reactive feedstocks may be limited by the supply rate of CO2. This rate limitation can be directly addressed by incorporating enzyme-catalyzed CO2 hydration. This study examined the effects of bovine carbonic anhydrase (BCA) and CO2-rich gas streams on the carbonation rate of brucite [Mg(OH)2], a highly reactive mineral. Alkaline brucite slurries were amended with BCA and supplied with 10% CO2 gas while aqueous chemistry and solids were monitored throughout the experiments (hours to days). In comparison to controls, brucite carbonation using BCA was accelerated by up to 240%. Nesquehonite [MgCO3·3H2O] precipitation limited the accumulation of hydrated CO2 species, apparently preventing BCA from catalyzing the dehydration reaction. Geochemical models reproduce observed reaction progress in all experiments, revealing a linear correlation between CO2 uptake and carbonation rate. Data demonstrates that carbonation in BCA-amended reactors remained limited by CO2 supply, implying further acceleration is possible.

Formations of calcium carbonate minerals by bacteria and its multiple applications

Biomineralization is a naturally occurring process in living organisms. In this review, we discuss microbially induced calcium carbonate precipitation (MICP) in detail. In the MICP process, urease plays a major role in urea hydrolysis by a wide variety of microorganisms capable of producing high levels of urease. We also elaborate on the different polymorphs and the role of calcium in the formation of calcite crystal structures using various calcium sources. Additionally, the environmental factors affecting the production of urease and carbonate precipitation are discussed. This MICP is a promising, eco-friendly alternative approach to conventional and current remediation technologies to solve environmental problems in multidisciplinary fields. Multiple applications of MICP such as removal of heavy metals and radionuclides, improve the quality of construction materials and sequestration of atmospheric CO₂ are discussed. In addition, we discuss other applications such as removal of calcium ions, PCBs and use of filler in rubber and plastics and fluorescent particles in stationary ink and stationary markers. MICP technology has become an efficient aspect of multidisciplinary fields. This report not only highlights the major strengths of MICP, but also discusses the limitations to application of this technology on a commercial scale.

Surface Engineering of Polypropylene Membranes with Carbonic Anhydrase-Loaded Mesoporous Silica Nanoparticles for Improved Carbon Dioxide Hydration

Carbonic anhydrase (CA) is a native enzyme that facilitates the hydration of carbon dioxide into bicarbonate ions. This study reports the fabrication of thin films of active CA enzyme onto a porous membrane substrate using layer-by-layer (LbL) assembly. Deposition of multilayer films consisting of polyelectrolytes and CA was monitored by quartz crystal microgravimetry, while the enzymatic activity was assayed according to the rates of p-nitrophenylacetate (p-NPA) hydrolysis and CO2 hydration. The fabrication of the films onto a nonporous glass substrate showed CO2 hydration rates of 0.52 ± 0.09 μmol cm(-2) min(-1) per layer of bovine CA and 2.6 ± 0.7 μmol cm(-2) min(-1) per layer of a thermostable microbial CA. The fabrication of a multilayer film containing the microbial CA on a porous polypropylene membrane increased the hydration rate to 5.3 ± 0.8 μmol cm(-2) min(-1) per layer of microbial CA. The addition of mesoporous silica nanoparticles as a film layer prior to enzyme adsorption was found to increase the activity on the polypropylene membranes even further to a rate of 19 ± 4 μmol cm(-2) min(-1) per layer of microbial CA. The LbL treatment of these membranes increased the mass transfer resistance of the membrane but decreased the likelihood of membrane pore wetting. These results have potential application in the absorption of carbon dioxide from combustion flue gases into aqueous solvents using gas-liquid membrane contactors.

Tethering of nicotinamide adenine dinucleotide inside hollow nanofibers for high-yield synthesis of methanol from carbon dioxide catalyzed by coencapsulated multienzymes

Enzymatic conversion of carbon dioxide (CO2) to fuel or chemicals is appealing, but is limited by lack of efficient technology for regeneration and reuse of expensive cofactors. Here we show that cationic polyelectrolyte-doped hollow nanofibers, which can be fabricated via a facile coaxial electrospinning technology, provide an ideal scaffold for assembly of cofactor and multienzymes capable of synthesizing methanol from CO2 through a cascade multistep reaction involving cofactor regeneration. Cofactor and four enzymes including formate, formaldehyde, alcohol, and glutamate dehydrogenases were in situ coencapsulated inside the lumen of hollow nanofibers by involving them in the core-phase solution for coaxial electrospinning, in which cationic polyelectrolyte was predissolved. The polyelectrolyte penetrating across the shell of the hollow nanofibers enabled efficient tethering and retention of cofactor inside the lumen via ion-exchange interactions between oppositely charged polyelectrolytes and cofactor. With carbonic anhydrase assembled on the outer surface of the hollow nanofibers for accelerating hydration of CO2, these five-enzymes-cofactor catalyst system exhibited high activity for methanol synthesis. Compared with methanol yield of only 36.17% using free enzymes and cofactor, the hollow nanofiber-supported system afforded a high value up to 103.2%, the highest reported value so far. It was believed that the linear polyelectrolytes acted as spacers to enhance the shuttling of cofactor between enzymes that were coencapsulated within near vicinity, thus improving the efficiency of the system. The immobilized system showed good stability in reusing. About 80% of its original productivity was retained after 10 reusing cycles, with a cofactor-based cumulative methanol yield reached 940.5%.

Carbonic anhydrases in industrial applications

Carbonic anhydrases (CAs) catalyze a fundamental reaction: the reversible hydration and dehydration of carbon dioxide (CO2) and bicarbonate ([Formula: see text]), respectively. Current methods for CO2 capture and sequestration are harsh, expensive, and require prohibitively large energy inputs, effectively negating the purpose of removing CO2 from the atmosphere. Due to CA's activity on CO2 there is increasing interest in using CAs for industrial applications such as carbon sequestration and biofuel production. A lot of work in the last decade has focused on immobilizing CA onto various supports for incorporation into CO2 scrubbing applications or devices. Although the proof of principle has been validated, current CAs being tested do not withstand the harsh industrial conditions. The advent of large-scale genome sequencing projects has resulted in several emerging efforts seeking out novel CAs from a variety of microorganisms, including bacteria, micro-, and macro-algae. CAs are also being investigated for their use in medical applications, such drug delivery systems and artificial lungs. This review also looks at possible downstream uses of captured and sequestered CO2, from using it to enhance oil recovery to incorporating it into useful and financially viable products.

Review of the enzymatic machinery of Halothermothrix orenii with special reference to industrial applications

Over the past few decades the extremes at which life thrives has continued to challenge our understanding of physiology, biochemistry, microbial ecology and evolution. Innovative culturing approaches, environmental genome sequencing, and whole genome sequencing have provided new opportunities for the biotechnological exploration of extremophiles. The whole genome sequencing of H. orenii has provided valuable insights not only into the survival and adaptation strategies of thermohalophiles but has also led to the identification of genes encoding biotechnologically relevant enzymes. The present review focuses on the purified and characterized enzymes from H. orenii including amylases, β-glucosidase, fructokinase, and ribokinase--along with uncharacterized but industrially important enzymes encoded by the genes identified in the genome such as β-galactosidases, mannosidases, pullulanases, chitinases, α-L-arabinofuranosidases and other glycosyl hydrolases of commercial interest. This review highlights the importance of the enzymes and their applications in different sectors and why future research for exploring the enzymatic machinery of H. orenii should focus on the expression, purification, and characterization of the novel proteins in H. orenii and their feasible application to pertinent industrial sectors. H. orenii is an anaerobe; genome sequencing studies have also revealed the presence of enzymes for gluconeogenesis and fermentation to ethanol and acetate, making H. orenii an attractive strain for the conversion of starch into bioethanol.

Immobilization and characterization of carbonic anhydrase purified from E. coli MO1 and its influence on CO₂ sequestration

The present investigation entails the immobilisation and characterisation of Escherichia coli MO1-derived carbonic anhydrase (CA) and its influence on the transformation of CO₂ to CaCO₃. CA was purified from MO1 using a combination of Sephadex G-75 and DEAE cellulose column chromatography, resulting in 4.64-fold purification. The purified CA was immobilised in chitosan-alginate polyelectrolyte complex (C-A PEC) with an immobilisation potential of 94.5 %. Both the immobilised and free forms of the enzyme were most active and stable at pH 8.2 and at 37 °C. The K(m) and V(max) of the immobilised enzyme were found to be 19.12 mM and 416.66 μmol min⁻¹ mg⁻¹, respectively; whereas, the K(m) and V(max) of free enzyme were 18.26 mM and 434.78 μmol min⁻¹ mg⁻¹, respectively. The presence of metal ions such as Cu²⁺, Fe²⁺, and Mg²⁺ stimulated the enzyme activity. Immobilised CA showed higher storage stability and maintained its catalytic efficiency after repeated operational cycles. Furthermore, both forms of the enzyme were tested for targeted application of the carbonation reaction to convert CO₂ to CaCO₃. The amounts of CaCO₃ precipitated over free and immobilised CA were 267 and 253 mg/mg of enzyme, respectively. The results of this study show that immobilised CA in chitosan-alginate beads can be useful for CO₂ sequestration by the biomimetic route.

Accelerated carbonation of brucite in mine tailings for carbon sequestration

Atmospheric CO(2) is sequestered within ultramafic mine tailings via carbonation of Mg-bearing minerals. The rate of carbon sequestration at some mine sites appears to be limited by the rate of CO(2) supply. If carbonation of bulk tailings were accelerated, large mines may have the capacity to sequester millions of tonnes of CO(2) annually, offsetting mine emissions. The effect of supplying elevated partial pressures of CO(2) (pCO(2)) at 1 atm total pressure, on the carbonation rate of brucite [Mg(OH)(2)], a tailings mineral, was investigated experimentally with conditions emulating those at Mount Keith Nickel Mine (MKM), Western Australia. Brucite was carbonated to form nesquehonite [MgCO(3) · 3H(2)O] at a rate that increased linearly with pCO(2). Geochemical modeling indicated that HCO(3)(-) promoted dissolution accelerated brucite carbonation. Isotopic and aqueous chemistry data indicated that equilibrium between CO(2) in the gas and aqueous phases was not attained during carbonation, yet nesquehonite precipitation occurred at equilibrium. This implies CO(2) uptake into solution remains rate-limiting for brucite carbonation at elevated pCO(2), providing potential for further acceleration. Accelerated brucite carbonation at MKM offers the potential to offset annual mine emissions by ~22-57%. Recognition of mechanisms for brucite carbonation will guide ongoing work to accelerate Mg-silicate carbonation in tailings.

Immobilization of carbonic anhydrase enzyme purified from Bacillus subtilis VSG-4 and its application as CO(2) sequesterer

The purification, immobilization, and characterization of carbonic anhydrase (CA) secreted by Bacillus subtilis VSG-4 isolated from tropical soil have been investigated in this work. Carbonic anhydrase was purified using ammonium sulfate precipitation, Sephadex-G-75 column chromatography, and DEAE-cellulose chromatography, achieving a 24.6-fold purification. The apparent molecular mass of purified CA obtained by SDS-PAGE was found to be 37 kD. The purified CA was entrapped within a chitosan-alginate polyelectrolyte complex (C-A PEC) hydrogel for potential use as an immobilized enzyme. The optimum pH and temperature for both free and immobilized enzymes were 8.2 and 37°C, respectively. The immobilized enzyme had a much higher storage stability than the free enzyme. Certain metal ions, namely, Co(2+), Cu(2+), and Fe(3+), increased the enzyme activity, whereas CA activity was inhibited by Pb(2+), Hg(2+), ethylenediamine tetraacetic acid (EDTA), 5,5'-dithiobis-(2-nitrobenzoic acid (DTNB), and acetazolamide. Free and immobilized CAs were tested further for the targeted application of the carbonation reaction to convert CO(2) to CaCO(3). The maximum CO(2) sequestration potential was achieved with immobilized CA (480 mg CaCO(3)/mg protein). These properties suggest that immobilized VSG-4 carbonic anhydrase has the potential to be used for biomimetic CO(2) 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.

Characterization of carbonic anhydrase II from Chlorella vulgaris in bio-CO2 capture

Carbonic anhydrase II (CA II) can catalyze the reversible hydration reaction of CO(2) at a maximum of 1.4 × 10(6) molecules of CO(2) per second. The crude intracellular enzyme extract containing CA II was derived from Chlorella vulgaris. A successful CO(2) capture experiment with the presence of calcium had been conducted on the premise that the temperature was conditioned at a scope of 30-40 °C, that the biocatalyst-nurtured algal growth period lasted 3 days, and that pH ranged from7.5 to 8.5. Ions of K(+), Na(+), Ca(2+), Co(2+), Cu(2+), Fe(3+), Mg(2+), Mn(2+), and Zn(2+) at 0.01, 0.1, and 0.5 M were found to exhibit no more than 30 % inhibition on the residual activity of the biocatalyst. It is reasonable to expect that calcification catalyzed by microalgae presents an alternative to geological carbon capture and sequestration through a chain of fundamental researches carried on under the guidance of sequestration technology.

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.

Biomimetic CO₂ sequestration using purified carbonic anhydrase from indigenous bacterial strains immobilized on biopolymeric materials

The present study deals with immobilization of purified CA and whole cell of Pseudomonas fragi, Micrococcus lylae, and Micrococcus luteus 2 on different biopolymer matrices. Highest enzyme immobilization was achieved with P. fragi CA (89%) on chitosan-KOH beads, while maximum cell immobilization was achieved with M. lylae (75%) on chitosan-NH(4)OH beads. A maximum increase of 1.08-1.18 fold stability between 35 and 55°C was observed for M. lylae immobilized CA. The storage stability was improved by 2.02 folds after immobilization. FTIR spectra confirmed the adsorption of CA on chitosan-KOH beads following hydrophilic interactions. Calcium carbonate precipitation was achieved using chitosan-KOH immobilized P. fragi CA. More than 2 fold increase in sequestration potential was observed for immobilized system as compared to free enzyme. XRD spectra revealed calcite as the dominant phase in biomimetically produced calcium carbonate.