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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

We identified the non-phosphorylated L-rhamnose metabolic pathway (Rha_NMP) genes that are homologous to those in the thermoacidophilic archaeon Thermoplasma acidophilum in the genome of the thermoacidophilic bacterium Sulfobacillus thermosulfidooxidans. However, unlike previously known 2-keto-3-deoxy-L-rhamnonate (L-KDR) dehydrogenase (KDRDH) which belongs to the short chain dehydrogenase/reductase superfamily, the putative KDRDHs in S. thermosulfidooxidans (Sulth_3557) and T. acidophilum (Ta0749) belong to the medium chain dehydrogenase/reductase (MDR) superfamily. We demonstrated that Sulth_3559 and Sulth_3557 proteins from S. thermosulfidooxidans function as L-rhamnose dehydrogenase and KDRDH, respectively. Sulth_3557 protein is an NAD(+)-specific KDRDH with optimal temperature and pH of 50 °C and 9.5, respectively. The K m and V max values for L-KDR were 2.0 mM and 12.8 U/mg, respectively. Sulth_3557 also showed weak 2,3-butanediol dehydrogenase activity. Phylogenetic analysis suggests that Sulth_3557 and its homologs form a new subfamily in the MDR superfamily. The results shown in this study imply that thermoacidophilic archaea metabolize L-rhamnose to pyruvate and L-lactate by using the MDR-family KDRDH similarly to that of the thermoacidophilic bacterium S. thermosulfidooxidans.

It is known that seaweeds differ greatly from land plants in their sugar composition. The current research on the L-lactic acid fermentation process focuses on land plant sugars as a carbon source, with the potential of seaweed sugars being largely ignored. This study examined the feasibility of seaweed biomass as a possible carbon source for the production of L-lactic acid, by comparing the fermentation of seaweed sugars (D-galactose, D-mannitol, L-rhamnose, D-glucuronic acid, and L-fucose) and land plant sugars (D-glucose, D-xylose, D-mannose, and L-arabinose). The experiments were repeated with 2 sugar acids (D-gluconic acid, D-glucaric acid) in order to investigate the effect of the degree of reduction of carbon source on the fermentation yield. This research also examined the effect of bacterial strain on the characteristics of fermentation reactions, by conducting L-lactic acid fermentation with 7 different Lactobacillus species. Taking into account the sugar composition of seaweed and the levels of lactic acid production from each pure sugar, it was possible to predict the lactic acid production yield of various seaweeds and land plants. From comparative analysis of the predicted lactic acid production yield, it was found that seaweeds are already comparable to lignocellulosics at the current stage of technology. If new technologies for the utilization of non-fermentable seaweed sugars are developed, seaweeds show promise as an even more useful biomass feedstock than lignocellulosics.

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