Intracellular carbonic anhydrase from Citrobacter freundii and its role in bio-sequestration

Plant -microbe assisted emerging contaminants (ECs) removal and carbon cycling

Continuous increase in the level of atmospheric CO₂ and environmental contaminates has aggravated various threats resulting from environmental pollution and climate change. Research into plant -microbe interaction has been a central concern of ecology for over the year. However, despite the clear contribution of plant -microbe to the global carbon cycle, the role of plant -microbe interaction in carbon pools, fluxes and emerging contaminants (ECs) removal are still a poorly understood. The use of plant and microbes in ECs removal and carbon cycling is an attractive strategy because microbes operate as biocatalysts to remove contaminants and plant roots offer a rich niche for their growth and carbon cycling. However, bio-mitigation of CO₂ and removal of ECs is still under research phase because of the CO₂ capture and fixation efficiency is too low for industrial purposes and cutting-edge removal methods have not been created for such emerging contaminants.

Simultaneous carbon dioxide sequestration and utilization for cadaverine production using dual promoters in engineered Escherichia coli strains

Human carbonic anhydrase II (hCAII) is a rapid-acting zinc-metalloenzyme that catalyzes CO₂ hydration reversibly, with encouraging applications in carbon capture, sequestration, and utilization (CCSU). However, biocatalyst durability is a major challenge. Herein, hCAII is emphasized in 4 different Escherichia coli strains and designated under dual promoters from sigma factor 70 (σ⁷⁰) and heat shock protein (HSP70A) to suppress the usage of inducer and stimulate activity in heat environments. As a result, hCAII under high-efficient dual promoters regulation retained high residual activity in CO₂ biomineralization of 68.8 % after 4 cycles at 40 °C. Moreover, co-expression of CA_C9 with lysine decarboxylase (CadA) simultaneously sequestered CO₂ release up to 95.7 % and increased cadaverine titer from 18.0 to 36.7 g/L by using E. coli MG1655. The remnant biomass from cadaverine synthesis sustained converting CO₂ to 57.9 mg-CaCO₃. Thus, the dual promoters design demonstrated the promising potential for CCSU through simultaneous CO₂ utilization and cadaverine synthesis.

Enzyme mediated transformation of CO2 into calcium carbonate using purified microbial carbonic anhydrase

In this study, a bacterial carbonic anhydrase (CA) was purified from Corynebacterium flavescens for the CO₂ conversion into CaCO₃. The synthesized CaCO₃ can be utilized in the papermaking industry as filler material, construction material and in steel industry. Herein, the CA was purified by using a Sephadex G-100 column chromatography having 29.00 kDa molecular mass in SDS-PAGE analysis. The purified CA showed an optimal temperature of 35 °C and pH 7.5. In addition, a kinetic study of CA using p-NPA as substrate showed V_max (166.66 μmoL/mL/min), K_m (5.12 mM), and K_cat (80.56 sec^-1) using Lineweaver Burk plot. The major inhibitors of CA activity were Na²⁺, K⁺, Mn²⁺, and Al³⁺, whereas Zn²⁺ and Fe²⁺ slightly enhanced it. The purified CA showed a good efficacy to convert the CO₂ into CaCO₃ with a total conversion rate of 65.05 mg CaCO₃/mg of protein. In silico analysis suggested that the purified CA has conserved Zn²⁺ coordinating residues such as His 111, His 113, and His 130 in the active site center. Further analysis of the CO₂ binding site showed conserved residues such as Val 132, Val 142, Leu 196, Thr 197, and Val 205. However, a substitution has been observed where Trp 208 of its closest structural homolog T. ammonificans CA is replaced with Arg 207 of C. flavescens. The presence of a hydrophilic mutation in the CO₂ binding hydrophobic region is a further subject of investigation.

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.

Optimisation of self-healing of bio-foamed concrete bricks pores using Bacillus tequilensis under different temperature and CO2 curing conditions

The self-healing of bio-concrete cracks and pores have been utilised worldwide to improve the properties of bio-concrete using different types of bacteria. Meanwhile, no published research was conducted to heal bio-foamed concrete bricks (B-FCB) pores using Bacillus tequilensis. Previous studies focused on the concentration of bacteria and neglect other factors that could affect the healing process. This research aimed to optimise the healing ratio of B-FCB pores using four factors: B. tequilensis concentration, concrete density, temperature and CO₂ concentration. Initial water absorption (IWA) and water absorption (WA) were used as responses in statistical methods, namely, factorial and response surface methodology (RSM). B. tequilensis species was isolated from cement kiln dust, produced in a powder form, then subjected to simulate test using a special medium consisting of foamed concrete materials to check the survival ability in B-FCB. SEM, EDX, and XRD were used to investigate the healing process of B-FCB pores. The results revealed that the decrement ratios of IWA and WA of B-FCB were 52.8% and 29.1% compared to FCB, respectively. SEM results reflect the healing that occurred in B-FCB pores, mostly healed via precipitation of CaCO₃ as demonstrated on the XRD results.

Recent Progress and Prospects in Catalytic Water Treatment

Presently, conventional technologies in water treatment are not efficient enough to completely mineralize refractory water contaminants. In this context, the implementation of catalytic processes could be an alternative. Despite the advantages provided in terms of kinetics of transformation, selectivity, and energy saving, numerous attempts have not yet led to implementation at an industrial scale. This review examines investigations at different scales for which controversies and limitations must be solved to bridge the gap between fundamentals and practical developments. Particular attention has been paid to the development of solar-driven catalytic technologies and some other emerging processes, such as microwave assisted catalysis, plasma-catalytic processes, or biocatalytic remediation, taking into account their specific advantages and the drawbacks. Challenges for which a better understanding related to the complexity of the systems and the coexistence of various solid-liquid-gas interfaces have been identified.

White Rann of Kachchh harbours distinct microbial diversity reflecting its unique biogeography

The understanding of sub-surface soil microbial diversity is limited at both saline and hypersaline ecosystems, even though salinity is found to affect the microbial community in aqueous and terrestrial environment. In this study, a phylo-taxonomy analysis as well as the functional characteristics of microbial community of flat salt basin of White Rann of Kachchh (WR), Gujarat, India was performed along the natural salinity gradient. The high throughput sequencing approach has revealed the numerical abundance of bacteria relative to the archaea. Salinity, TOC, EC and sulphate concentration might be the primary driver of the community distribution along the transect at WR. The much anticipated effect of salinity gradient on the microbial composition surprisingly turned out to be more speculative, with little variance in the community composition along the spatial distance of WR. The metabolic pathways involved in energy metabolism (like carbon, nitrogen, sulphur) along with environmental adaptive genes (like osmotic and oxidative stress response, heat and cold shock genes clusters) were abundantly annotated from shot-gun metagenomic study. The carbonic anhydrase harbouring bacteria Bacillus sp. DM4CA1 was isolated from WR, having a catalytic ability for converting the gaseous carbon dioxide in presence of calcium carbonate into calcite at 25 % higher rate as compared to non-harbouring strains. The enzyme has a role in multiple alternative pathways in microbial metabolism. With the array of results obtained, the study could become the new reference for understanding the diversity structure and functional characteristics of the microbial community of terrestrial saline environment.

Optimization of Bio-Foamed Concrete Brick Strength via Bacteria Based Self-Healing and Bio-Sequestration of CO2

This research aimed to optimize the compressive strength of bio-foamed concrete brick (B-FCB) via a combination of the natural sequestration of CO₂ and the bio-reaction of B. tequilensis enzymes. The experiments were guided by two optimization methods, namely, 2^k factorial and response surface methodology (RSM). The 2^k factorial analysis was carried out to screen the important factors; then, RSM analysis was performed to optimize the compressive strength of B-FCB. Four factors, namely, density (D), B. tequilensis concentration (B), temperature (T), and CO₂ concentration, were selectively varied during the study. The optimum compressive strength of B-FCB was 8.22 MPa, as deduced from the following conditions: 10% CO₂, 3 × 10⁷ cell/mL of B, 27 °C of T and 1800 kg/m³ of D after 28 days. The use of B. tequilensis in B-FCB improved the compressive strength by 35.5% compared to the foamed concrete brick (FCB) after 28 days. A microstructure analysis by scanning electronic microscopy (SEM), energy dispersive X-ray (EDX) and X-ray diffraction analysis (XRD) reflected the changes in chemical element levels and calcium carbonate (CaCO₃) precipitation in the B-FCB pores. This was due to the B. tequilensis surface reactions of carbonic anhydrase (CA) and urease enzyme with calcium in cement and sequestered CO₂ during the curing time.

Mechanism of carbonate mineralization induced by microbes: Taking Curvibacter lanceolatus strain HJ-1 as an example

Microbial-induced carbonate precipitation is important in the global carbon cycle, especially in fixing atmospheric CO₂. Many simulation experiments have shown that microbes can induce carbonate precipitation, although there is no established understanding of the mechanism. In this study, several mineralization experiments were performed using Curvibacter lanceolatus strain HJ-1, including its secreted extracellular polymeric substances (EPS) and carbonic anhydrase (CA). We found that strain HJ-1, EPS, and CA could promote carbonate precipitation if compared with the respective control experiments (CK). Also, both HJ-1 and EPS1 experiments contained calcite and aragonite, whereas CA experiments formed calcite only. Therefore, HJ-1 and EPS is favorable for carbonate precipitation, especially for aragonite. Besides, the formation of calcite in the EPS2 experiments indicated that EPS contains a trace amount of CA, which might promote CO₂ hydration and eventually lead to carbonate precipitation. It was suggested that CA only provide CO₃^2- for the formation of carbonate minerals. In the absence of exogenous HCO₃-, the optimized calcification rate followed the order: HJ-1(49.5 %) > CA(6.6 %) > EPS2(4.1 %). In addition, MICP mechanisms was studied, an increase in pH and CO₂ hydration by CA play synergetic roles in providing supersaturated alkaline conditions in the system with bacteria. Finally, bacterial cells and EPS promote the formation of calcite and aragonite by acting as nucleation sites.

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.