Efficient CO2-Reducing Activity of NAD-Dependent Formate Dehydrogenase from Thiobacillus sp KNK65MA for Formate Production from CO2 Gas

NAD-dependent formate dehydrogenase (FDH) from Candida boidinii (CbFDH) has been widely used in various CO2 reduction systems but its practical applications are often impeded due to low CO2-reducing activity. In this study, we demonstrated superior CO2-reducing properties of FDH from Thiobacillus sp. KNK65MA (TsFDH) for production of formate from CO2 gas. To discover more efficient CO2-reducing FDHs than a reference enzyme e. CbFDH, five FDHs were selected with biochemical properties and then, their CO2-reducing activities were evaluated. All FDHs including CbFDH showed better CO2-reducing activities at acidic pHs than at neutral pHs and four FDHs were more active than CbFDH in the CO2 reduction reaction. In particular, the FDH from Thiobacillus sp. KNK65IVIA (TsFDH) exhibited the highest CO2-reducing activity and had a dramatic preference for the reduction reaction, i.e., a 84.2-fold higher ratio of CO2 reduction to formate oxidation in catalytic efficiency (k(cat)/K-B) compared to CbFDH. Formate was produced from CO2 gas using TsFDH and CbFDH, and TsFDH showed a 5.8-fold higher formate production rate than CbFDH. A sequence and structural comparison showed that FDHs with relatively high CO2-reducing activities had elongated N- and C-terminal loops. The experimental results demonstrate that TsFDH can be an alternative to CbFDH as a biocatalyst in CO2 reduction systemsope

Machine learning based predictive model for methanol steam reforming with technical, environmental, and economic perspectives

To overcome limitations of conventional H2 production approaches such as steam methane reforming (SMR) in a membrane reactor (MR) such as large CO2 emission and deactivation of catalyst and membrane, a promising alternative H2 production system of methanol steam reforming (MSR) in serial reactors and membrane filters is reported here, affording its high product yield and a compact design. In this study, technical, environmental, and economic feasibility according to 12 techno-economic parameters and detailed effects of each parameter for this H2 production system are comprehensively investigated with a machine learning (ML) based predictive model in the following steps: (1) process simulation using Aspen Plus?? with detailed thermodynamic phenomena and environmental performance; (2) numerical model using MATLAB?? based on technical and environmental performance from the process simulation results; (3) ML-based predictive model having outputs of H2 production rate, CO2 emission, and unit H2 production cost feasibility trained by 12,000 data sets from a numerical model. It is well noted from this study that # of reactors and operating temperature for technical performance, # of reactors and S/C ratio for environmental performance, and operating temperature, # of reactors, reactant, and labor for economic performance are reported as most influential factors

Communication-Highly Efficient Electroenzymatic NADH Regeneration by an Electron-Relay Flavoenzyme

Efficient cofactor regeneration is essential for the utilization of many oxidoreductases. Herein, the beta-subunit of formate dehydrogenase 1 from Methylobacterium extorquens AM1 (MeFDH1-beta) was employed as a novel electroactive biocatalyst for electroenzymatic NADH regeneration for the first time. MeFDH1-beta showed much better properties in both catalytic activity (a turnover frequency of 3,600 hr(-1)) and current efficiency (ca. 98%) than a conventional rhodium (III)-based chemical catalyst (M = [Cp*Rh(bpy)H2O](2+), Cp* = C5Me5, bpy = 2,2'-bipyridine) and a traditional biocatalyst (diaphorase). (C) 2016 The Electrochemical Society. All rights reservedclos

Expression of the NAD-dependent FDH1 beta-subunit from Methylobacterium extorquens AM1 in Escherichia coli and its characterization

The efficient regeneration of nicotinamide cofactors is an important process for industrial applications because of their high cost and stoichiometric requirements. In this study, the FDH1 beta-subunit of NAD-dependent formate dehydrogenase from Methylobacterium extorquens AM1 was heterologously expressed in Escherichia coli. It showed water-forming NADH oxidase (NOX-2) activity in the absence of its alpha-subunit. The beta-subunit oxidized NADH and generated NAD(+). The enzyme showed a low NADH oxidation activity (0.28 U/mg enzyme). To accelerate electron transfer from the enzyme to oxygen, four electron mediators were tested; flavin mononucleotide, flavin adenine dinucleotide, benzyl viologen (BV), and methyl viologen. All tested electron mediators increased enzyme activity; addition of 250 mu M BV resulted in the largest increase in enzyme activity (9.98 U/mg enzyme; a 35.6-fold increase compared with that in the absence of an electron mediator). Without the aid of an electron mediator, the enzyme had a substrate-binding affinity for NADH (K (m)) of 5.87 mu M, a turnover rate (k (cat)) of 0.24/sec, and a catalytic efficiency (k (cat)/K (m)) of 41.31/mM/sec. The addition of 50 mu M BV resulted in a 22.75-fold higher turnover rate (k (cat), 5.46/sec) and a 2.64-fold higher catalytic efficiency (k (cat)/K (m), 107.75/mM/sec)clos

Outlook of industrial-scale green hydrogen production via a hybrid system of alkaline water electrolysis and energy storage system based on seasonal solar radiation

Hydrogen has been considered as a clean energy carrier by generating electricity via fuel cells without carbon dioxide emissions; however, in the current stage, most hydrogen is produced by a steam methane reforming, emitting carbon dioxide as a by product, together. In this context, a green hydrogen production system, which is consisted of water electrolysis and a renewable energy plant, should be expanded to prepare for the upcoming hydrogen society in the future. A techno-economic analysis is carried out for green hydrogen production based on seasonal solar radiation data in the case of the single and the hybrid system, which is designed as only alkaline water electrolyzer and a combination of alkaline water electrolyzer and energy storage system. In addition, a carbon footprint analysis is performed to quantify the carbon dioxide emissions for the proposed systems. And the optimal scale of alkaline water electrolyzer and energy storage system is figured out via a genetic algorithm considering a carbon tax on emitted carbon dioxide. Based on itemized cost estimation results, 6.55 and 6.88 USD kgH(2)(-1) of unit hydrogen production costs were obtained for the case of a hybrid and a single system, respectively. Further, the results present that the hybrid system is preferred when Li-ion battery costs decrease to under 79.67 USD kWh(-1). In addition, the capital cost is a crucial factor to figure out the optimized alkaline water electrolyzer scale and energy storage system capacity that set the optimized size is important to minimize the unit hydrogen production cost. Finally, the effort to reduce the capital cost to produce the green hydrogen is necessary when increasing trend of carbon dioxide tax is considered

Electro-biocatalytic production of formate from carbon dioxide using an oxygen-stable whole cell biocatalyst

The use of biocatalysts to convert CO2 into useful chemicals is a promising alternative to chemical conversion. In this study, the electro-biocatalytic conversion of CO2 to formate was attempted with a whole cell biocatalyst. Eight species of Methylobacteria were tested for CO2 reduction, and one of them, Methylobacterium extorquens AM1, exhibited an exceptionally higher capability to synthesize formate from CO2 by supplying electrons with electrodes, which produced formate concentrations of up to 60 mM. The oxygen stability of the biocatalyst was investigated, and the results indicated that the whole cell catalyst still exhibited CO2 reduction activity even after being exposed to oxygen gas. From the results, we could demonstrate the electro-biocatalytic conversion of CO2 to formate using an obligate aerobe, M. extorquens AM1, as a whole cell biocatalyst without providing extra cofactors or hydrogen gas. This electro-biocatalytic process suggests a promising approach toward feasible way of CO2 conversion to formate.clos

Enzymatic photosynthesis of formate from carbon dioxide coupled with highly efficient photoelectrochemical regeneration of nicotinamide cofactors

We present the photoelectrochemical (PEC) regeneration of nicotinamide cofactors (NADH) coupled with the enzymatic synthesis of formate from CO2 towards mimicking natural photosynthesis. The water oxidation-driven PEC platform exhibited high yield and the rate of NADH regeneration was compared to many other homogeneous, photochemical systems. We successfully coupled solar-assisted NADH reduction with enzymatic CO2 reduction to formate under continuous CO2 injection.close

Sunlight-assisted, biocatalytic formate synthesis from CO2 and water using silicon-based photoelectrochemical cells

We report on a silicon-based photoelectrochemical cell that integrates a formate dehydrogenase from Thiobacillus sp. (TsFDH) to convert CO2 to formate using water as an electron donor under visible light irradiation and an applied bias. Our current study suggests that the deliberate integration of biocatalysis to a light-harvesting platform could provide an opportunity to synthesize valuable chemicals with the use of earth-abundant materials and sustainable resources.clos

Structural comparison of TsFDH and CbFDH.

<p>Structural comparison of the A) N- and B) C-terminal loops of TsFDH (green, modeled using 2NAD) and CbFDH (cyan, pdb code: 2FSS). The elongated N- and C-terminal loops are shown in blue.</p