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Background  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.    Results  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 CaCl 2  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 CaCl 2 , 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.    Conclusions  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 CaCl 2 . The direct and highly productive conversion process from  A. platensis  via yeast fermentation could be applied to multiple industrial bulk chemicals.    Electronic supplementary material  The online version of this article (10.1186/s13068-018-1050-y) contains supplementary material, which is available to authorized users.

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