Abstract
Caldicellulosiruptor bescii is the most thermophilic cellulolytic organism yet identified (Topt 78 °C). It grows on untreated plant biomass and has an established genetic system thereby making it a promising microbial platform for lignocellulose conversion to bio-products. Here, we investigated the ability of engineered C. bescii to generate alcohols from carboxylic acids. Expression of aldehyde ferredoxin oxidoreductase (aor from Pyrococcus furiosus) and alcohol dehydrogenase (adhA from Thermoanaerobacter sp. X514) enabled C. bescii to generate ethanol from crystalline cellulose and from biomass by reducing the acetate produced by fermentation. Deletion of lactate dehydrogenase in a strain expressing the AOR–Adh pathway increased ethanol production. Engineered strains also converted exogenously supplied organic acids (isobutyrate and n-caproate) to the corresponding alcohol (isobutanol and hexanol) using both crystalline cellulose and switchgrass as sources of reductant for alcohol production. This is the first instance of an acid to alcohol conversion pathway in a cellulolytic microbe.
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Acknowledgements
This material is based on work supported by the U.S. Department of Energy, Office of Science, Office of Biological and Environmental Research (DE-SC0019391) and by a grant (DE-PS02-06ER64304) from the Bioenergy Science Center at Oak Ridge National Laboratory. We thank Israel Scott, Laura Lee, Piyum Khatibi, Jeff Zurawski, Jonathan Conway, Diep Nguyen, Farris Poole, Mirko Basen, and Matthew Keller for helpful discussions, and Daewhan Chung and Janet Westpheling for providing C. bescii strain JWCB018 and plasmids pDCW121 and pDCW88.
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Rubinstein, G.M., Lipscomb, G.L., Williams-Rhaesa, A.M. et al. Engineering the cellulolytic extreme thermophile Caldicellulosiruptor bescii to reduce carboxylic acids to alcohols using plant biomass as the energy source. J Ind Microbiol Biotechnol 47, 585–597 (2020). https://doi.org/10.1007/s10295-020-02299-z
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DOI: https://doi.org/10.1007/s10295-020-02299-z