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Biotechnol Biofuels. 2018 Feb 27;11:50. doi: 10.1186/s13068-018-1050-y. eCollection 2018.

Direct and highly productive conversion of cyanobacteria Arthrospira platensis to ethanol with CaCl2 addition.

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1Graduate School of Science, Technology, and Innovation, Kobe University, 1-1 Rokkodai, Nada-ku, Kobe, 657-8501 Japan.
2Core Research for Evolutional Science and Technology, Japan Science and Technology Agency, 3-5 Sanbancho, Chiyoda-ku, Tokyo, 102-0075 Japan.
8Present Address: Biological Resources and Post-Harvest Division, Japan International Research Center for Agricultural Sciences (JIRCAS), 1-1 Ohwashi, Tsukuba, Ibaraki 305-8686 Japan.
3Graduate School of Engineering, Kobe University, 1-1 Rokkodai, Nada-ku, Kobe, 657-8501 Japan.
4Department of Chemical Engineering, National Cheng Kung University, Tainan, 701 Taiwan.
5Research Center for Energy Technology and Strategy, National Cheng Kung University, Tainan, 701 Taiwan.
6Center for Bioscience and Biotechnology, National Cheng Kung University, Tainan, 701 Taiwan.
7Biomass Engineering Program, RIKEN, 1-7-22 Suehiro, Tsurumi-ku, Yokohama, 230-0045 Japan.



The cyanobacterium Arthrospira platensis shows promise as a carbohydrate feedstock for biofuel production. The glycogen accumulated in A. platensis can be extracted by lysozyme-degrading the peptidoglycan layer of the bacterial cell walls. The extracted glycogen can be converted to ethanol through hydrolysis by amylolytic enzymes and fermentation by the yeast Saccharomyces cerevisiae. Thus, in the presence of lysozyme, a recombinant yeast expressing α-amylase and glucoamylase can convert A. platensis directly to ethanol, which would simplify the procedure for ethanol production. However, the ethanol titer and productivity in this process are lower than in ethanol production from cyanobacteria and green algae in previous reports.


To increase the ethanol titer, a high concentration of A. platensis biomass was employed as the carbon source for the ethanol production using a recombinant amylase-expressing yeast. The addition of lysozyme to the fermentation medium increased the ethanol titer, but not the ethanol productivity. The addition of CaCl2 increased both the ethanol titer and productivity by causing the delamination of polysaccharide layer on the cell surface of A. platensis. In the presence of lysozyme and CaCl2, ethanol titer, yield, and productivity improved to 48 g L-1, 93% of theoretical yield, and 1.0 g L-1 h-1 from A. platensis, corresponding to 90 g L-1 of glycogen.


We developed an ethanol conversion process using a recombinant amylase-expressing yeast from A. platensis with a high titer, yield, and productivity by adding both lysozyme and CaCl2. The direct and highly productive conversion process from A. platensis via yeast fermentation could be applied to multiple industrial bulk chemicals.


Amylase-displaying yeast; Cyanobacteria; Ethanol conversion; Glycogen extraction; Organic nutrient; Polysaccharide layer

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