Adaptively evolved Escherichia coli for improved ability of formate utilization as a carbon source in sugar???free conditions

Background: Formate converted from CO2 reduction has great potential as a sustainable feedstock for biological production of biofuels and biochemicals. Nevertheless, utilization of formate for growth and chemical production by microbial species is limited due to its toxicity or the lack of a metabolic pathway. Here, we constructed a formate assimilation pathway in Escherichia coli and applied adaptive laboratory evolution to improve formate utilization as a carbon source in sugar-free conditions. Results: The genes related to the tetrahydrofolate and serine cycles from Methylobacterium extorquens AM1 were overexpressed for formate assimilation, which was proved by the 13C-labeling experiments. The amino acids detected by GC/MS showed significant carbon labeling due to biomass production from formate. Then, 150 serial subcultures were performed to screen for evolved strains with improved ability to utilize formate. The genomes of evolved mutants were sequenced and the mutations were associated with formate dehydrogenation, folate metabolism, and biofilm formation. Last, 90 mg/L of ethanol production from formate was achieved using fed-batch cultivation without addition of sugars. Conclusion: This work demonstrates the effectiveness of the introduction of a formate assimilation pathway, combined with adaptive laboratory evolution, to achieve the utilization of formate as a carbon source. This study suggests that the constructed E. coli could serve as a strain to exploit formate and captured CO2

Molecular Rh(III) and Ir(III) Catalysts Immobilized on Bipyridine-Based Covalent Triazine Frameworks for the Hydrogenation of CO2 to Formate

The catalytic reactivity of molecular Rh(III)/Ir(III) catalysts immobilized on two- and three-dimensional Bipyridine-based Covalent Triazine Frameworks (bpy-CTF) for the hydrogenation of CO2 to formate has been described. The heterogenized Ir complex demonstrated superior catalytic efficiency over its Rh counterpart. The Ir catalyst immobilized on two-dimensional bpy-CTF showed an improved turnover frequency and turnover number compared to its three-dimensional counterpart. The two-dimensional Ir catalyst produced a maximum formate concentration of 1.8 M and maintained its catalytic efficiency over five consecutive runs with an average of 92% in each cycle. The reduced activity after recycling was studied by density functional theory calculations, and a plausible leaching pathway along with a rational catalyst design guidance have been proposed

Design Strategy toward Recyclable and Highly Efficient Heterogeneous Catalysts for the Hydrogenation of CO₂ to Formate

One bottleneck in the realization of CO₂ conversion into value-added compounds is the lack of catalysts with both excellent activity and recyclability. Herein, a catalyst is designed for the hydrogenation of CO₂ to formate to boost up these features by considering the leaching pathway of previously reported heterogenized catalyst; the design strategy incorporates oxyanionic ligand(s) in the coordination sphere to provide a pathway for both preventing the deleterious interactions and assisting the heterolysis of H₂. The tailored heterogenized catalyst, [bpy-CTF-Ru­(acac)₂]­Cl, demonstrated excellent recyclability over consecutive runs with a highest turnover frequency of 22 700 h^–1, and produced a highest formate concentration of 1.8 M in 3 h. This work is significant in elucidating new principles for the development of industrially viable hydrogenation catalysts

A Covalent Triazine Framework, Functionalized with Ir/N-Heterocyclic Carbene Sites, for the Efficient Hydrogenation of CO₂ to Formate

Functionalizing the recently developed porous materials such as porous organic frameworks and coordination polymer networks with active homogeneous catalytic sites would offer new opportunities in the field of heterogeneous catalysis. In this regard, a novel covalent triazine framework functionalized with an Ir­(III)-N-heterocyclic carbene complex was synthesized and characterized to have a coordination environment similar to that of its structurally related molecular Ir complex. Because of the strong σ-donating and poor π-accepting characters of the N-heterocyclic carbene (NHC) ligand, the heterogenized Ir-NHC complex efficiently catalyzes the hydrogenation of CO₂ to formate with a turnover frequency of up to 16 000 h^–1 and a turnover number of up to 24 300; these are the highest values reported to date in heterogeneous catalysis for the hydrogenation of CO₂ to formate