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A whole cell biocatalyst for cellulosic ethanol production from dilute acid-pretreated corn stover hydrolyzates

Ryu, Seunghyun, Karim, Muhammad Nazmul
Applied microbiology and biotechnology 2011 v.91 no.3 pp. 529-542
Clostridium cellulolyticum, Escherichia coli, cellulose, corn stover, endo-1,4-beta-glucanase, ethanol, ethanol fermentation, ethanol production, glucose, proteins, saccharification, temperature
In this research, a recombinant whole cell biocatalyst was developed by expressing three cellulases from Clostridium cellulolyticum—endoglucanase (Cel5A), exoglucanase (Cel9E), and β-glucosidase—on the surface of the Escherichia coli LY01. The modified strain is identified as LY01/pRE1H-AEB. The cellulases were displayed on the surface of the cell by fusing with an anchor protein, PgsA. The developed whole cell biocatalyst was used for single-step ethanol fermentation using the phosphoric acid-swollen cellulose (PASC) and the dilute acid-pretreated corn stover. Ethanol production was 3.59 ± 0.15 g/L using 10 g/L of PASC, which corresponds to a theoretical yield of 95.4 ± 0.15%. Ethanol production was 0.30 ± 0.02 g/L when 1 g/L equivalent of glucose in the cellulosic fraction of the dilute sulfuric acid-pretreated corn stover (PCS) was fermented for 84 h. A total of 0.71 ± 0.12 g/L ethanol was produced in 48 h when the PCS was fermented in the simultaneous saccharification and co-fermentation mode using the hemicellulosic (1 g/L of total soluble sugar) and as well as the cellulosic (1 g/L of glucose equivalent) parts of PCS. In a control experiment, 0.48 g/L ethanol was obtained from 1 g/L of hemicellulosic PCS. It was concluded that the whole cell biocatalyst could convert both cellulosic and hemicellulosic substrates into ethanol in a single reactor. The developed C. cellulolyticum–E. coli whole cell biocatalyst also overcame the incompatible temperature problem of the frequently reported fungal–yeast systems.