Non-ionic surfactant integrated extraction of exopolysaccharides from engineered Synechocystis sp. PCC 6803 under fed-batch mode facilitates the sugar-rich syrup production for ethanol fermentation br

As a promising alternative fuel, ethanol has attracted extensive attention while still facing the challenges asso-ciated with multiple treatment of complex biomass. Exopolysaccharides (EPS) are a type of carbohydrate polymer produced extracellularly, which are used as an alternative raw material in the present study. The model cyanobacterium Synechocystis sp. PCC 6803 was used to produce the EPS, in which the glycogen synthesis pathway was inactivated to enhance the EPS accumulation. To extract EPS from cyanobacteria, various sur-factants were used to improve subsequent hydrolysis and fermentation processes. In fed-batch extraction, Triton X-100 was effective for 5 runs, while polyethylene glycol, Tween-20 and Tween-80 were effective for 4 runs. The Tween-80 extracted C-EPS was hydrolysed and the highest fermentable sugar yield of about 54.8 % and 89 % of theoretical maximum were observed in enzymatic and acid hydrolysis respectively. Notably, the hydrolysates obtained from enzymatic and acid hydrolysis produced the ethanol yield of about 90 and 83 % of theoretical maximum respectively. Overall results indicate that the use of microscale EPS obtained from engineered Syn-echocystis sp. PCC 6803 is suitable for fermentative ethanol production. Moreover, the use of single surfactant in extraction process enhances the subsequent hydrolysis and fermentation processes, which can be beneficial in terms of process integration.

Automated summary

This study found that microscale EPS obtained from engineered Synechocystis sp. PCC 6803 can be effectively used for ethanol production. The use of a single surfactant in the extraction process enhances subsequent hydrolysis and fermentation processes.