Cynanobacteria: An Alternate to Lignocellulosic Biomass in Biofuel Production

Photosynthetic microorganisms have shown potential as an alternate resource for biofuel and bioproduct production. They grow much faster than terrestrial plants and can be cultivated in marginal areas and will not compete with plant-based food and feed production. Cyanobacteria, one of the most abundant photosynthetic microorganisms, can produce high-value bioproducts and have been mass-cultivated for nutritional supplement. However, the direct use of biomass from cyanobacteria for the generation of biofuels and other bioproducts is underexplored. In this study, biomass from the photosynthetic marine cyanobacterium, Synechococcus sp. PCC 7002, was fermented using yeast to produce bioethanol.

The cyanobacterium accumulated a total carbohydrate content of about 60% of cell dry weight under nitrate limitation. The cyanobacterial cells were harvested and subjected to enzymatic hydrolysis. The enzymatic hydrolysate was then fermented into ethanol by Saccharomyces cerevisiae without further treatment. All enzyme treatments and fermentations were carried out in the residual growth medium of the cyanobacteria with the only modification being that pH level was optimal. The highest ethanol yield was at 0.27g ethanol/gram of cell dry weight and highest concentration obtained was 30 g ethanol/liter. About 90% of the glucose in the biomass was converted to ethanol. The cyanobacterial hydrolysate was rapidly fermented even in the absence of any other nutrient additions to the fermentation medium.