Virus infection of Chlorella variabilis and enzymatic saccharification of algal biomass for bioethanol production

• Viral infection is a feasible approach to disrupt microalgal cell walls.
• Bioethanol can be produced from viral lysed algal biomass.
• Cytoplasmic starch was not consumed during the period of viral lysis.
• Starch degrading enzyme was required to hydrolyze starch in viral lysate.

Experiments were conducted to investigate the application of virus infection and amylolytic enzyme treatment on sugar release from Chlorella variabilis NC64A and bioethanol production from released sugars via Escherichia coli KO11 fermentation. Chlorella variabilis NC64A accumulated starch when it was cultured in a nitrogen-limited medium. The accumulated starch was not consumed during viral infection based on analysis of sugars released during infection. Both amylolytic enzyme addition and virus infection increased the hydrolysis of carbohydrates. Addition of amylolytic enzymes increased the release of glucose from algal biomass while virus addition increased the release of non-glucose neutral sugars. The combination of enzyme addition and virus infection also resulted in the highest ethanol production after fermentation. Acetic acid was generated as a co-product during fermentation in all sets of experiments. This study demonstrated that infection of microalgae with an algal virus resulted in disruption and hydrolysis of algal biomass to generate fermentable sugars.