Carbon monoxide dehydrogenase (CODH)-catalyzed oxidation of CO to CO 2 provides a promising means of removal of toxic and waste CO from industrial ue gas despite of the lack of active and stable enzymes in the atmosphere. Herein we present rationally and selectively redesigned ChCODH-II (Carboxydothermus hydrogenoformans) variants by engineering gas tunnels in order for O 2 -tolerant CODHs to catalyze e cient CO oxidation under oxygen (O 2 ). Using the redesigned ChCODH-II A559W and A559H variants showing 42-and 128-fold elevation of O 2 tolerance, respectively, complete CO removal was achieved under a near-atmospheric condition. Moreover, these variants e ciently removed CO from industrial ue gas (Linz-Donawiz converter Gas: LDG) discharged from a steel mill despite the high O 2 level (13.4%) during successful and repeated reuse after immobilized on Ni-NTA agarose beads. Our study will provide insights into redesigning the transformation of O 2 -sensitive CODHs into tolerant enzymes for use as workhorses for conversion of toxic or waste gases into safe or value-added chemicals. MainLarge amounts of CO pollutants are emitted from natural sources as well as man-made processes 1 (e.g. annually over 219 billion Nm 3 of CO-containing ue gases from POSCO) 2,3 . Carbon monoxide (CO), the most abundant air pollutant found in the atmosphere other than CO 2 according to the OECD database (https://stats.oecd.org, air emissions source in 2017), can provide su cient carbon and energy sources for converting waste gas to fuels and chemicals through a clean and sustainable method. To convert

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Solar hydrogen production is one of the ultimate technologies needed to realize a carbon-neutral, sustainable society. However, an energy-intensive water oxidation half-reaction together with the poor performance of conventional inorganic photocatalysts have been big hurdles for practical solar hydrogen production. Here we present a photoelectrochemical cell with a record high photocurrent density of 19.8 mA cm−2 for hydrogen production by utilizing a high-performance organic–inorganic halide perovskite as a panchromatic absorber and lignocellulosic biomass as an alternative source of electrons working at lower potentials. In addition, value-added chemicals such as vanillin and acetovanillone are produced via the selective depolymerization of lignin in lignocellulosic biomass while cellulose remains close to intact for further utilization. This study paves the way to improve solar hydrogen productivity and simultaneously realize the effective use of lignocellulosic biomass.

Ferredoxin-dependent metabolic engineering of electron transfer circuits has been developed to enhance redox efficiency in the field of synthetic biology, e.g., for hydrogen production and for reduction of flavoproteins or NAD(P)+. Here, we present the bioconversion of carbon monoxide (CO) gas to formate via a synthetic CO:formate oxidoreductase (CFOR), designed as an enzyme complex for direct electron transfer between non-interacting CO dehydrogenase and formate dehydrogenase using an electron-transferring Fe-S fusion protein. The CFOR-introduced Thermococcus onnurineus mutant strains showed CO-dependent formate production in vivo and in vitro. The maximum formate production rate from purified CFOR complex and specific formate productivity from the bioreactor were 2.2 ± 0.2 μmol/mg/min and 73.1 ± 29.0 mmol/g-cells/h, respectively. The CO-dependent CO2 reduction/formate production activity of synthetic CFOR was confirmed, indicating that direct electron transfer between two unrelated dehydrogenases was feasible via mediation of the FeS-FeS fusion protein.

Anaerobic bioprocessing is preferred because of its economic advantages. However, low productivity and decreased growth of the host strain have limited the use of the anaerobic process. Anaerobic respiration can be applied to anoxic processing using formate and nitrate metabolism to improve the productivity of value-added metabolites. A isobutanol-producing strains is constructed using Enterobacter aerogenes as a host strain by metabolic engineering approaches. The byproduct pathway (ldhA, budA, and pflB) is knocked out, and heterologous keto-acid decarboxylase (kivD) and alcohol dehydrogenase (adhA) are expressed along with the L-valine synthesis pathway (ilvCD and budB). The pyruvate formate-lyase mutant shows decreased growth rates when cultivated in semi-anaerobic conditions, which results in a decline in productivity. When formate and nitrate are supplied in the culture medium, the growth rates and amount of isobutanol production is restored (4.4 g L , 0.23 g g glucose, 0.18 g L h ). To determine the function of the formate and nitrate coupling reaction system, the mutant strains that could not utilize formate or nitrate is contructed. Decreased growth and productivity are observed in the nitrate reductase (narG) mutant strain. This is the first report of engineering isobutanol-producing E. aerogenes to increase strain fitness via augmentation of formate and nitrate metabolism during anaerobic cultivation.