Cyanobacterial biomass as carbohydrate and nutrient feedstock for bioethanol production by yeast fermentation
Thursday, May 1, 2014: 4:00 PM
Grand Ballroom A-C, lobby level (Hilton Clearwater Beach)
Klaus Benedikt Möllers1, David Cannella2, Henning Jørgensen2 and Niels-Ulrik Frigaard1, (1)Department of Biology, University of Copenhagen, Helsingør, Denmark, (2)Faculty of Science, University of Copenhagen, Frederiksberg C, Denmark
Photosynthetic biomass and microbial bioconversions are promising resources for the generation of biofuels and other bioproducts. However, rapid, high-yield, and simple processes are essential for successful applications. Here, biomass from the rapidly growing marine photosynthetic cyanobacterium Synechococcus was fermented by yeast to bioethanol.

The cyanobacterium wild strain was cultivated under nitrogen starvation for 48 hours, during which the cell culture dry weight increased by 60 fold, and the cells accumulated a total glucose content of about 60% of cell dry weight. The cyanobacterial cells were harvested by centrifugation and subjected to enzymatic hydrolysis using lysozyme and two alpha-glucanases. This enzymatic hydrolysate was fermented without further treatment to ethanol by Saccharomyces cerevisiae. All enzyme treatments and fermentations were carried out in the residual growth medium of the cyanobacteria, only adjusted for optimal pH. The highest ethanol yield obtained was 30 g ethanol L‑1. About 90% of the glucose in the biomass was converted to ethanol. The cyanobacterial hydrolysate was rapidly fermented (up to 20 g ethanol L-1 day-1) even in the absence of any other nutrient additions to the fermentation medium.

Cyanobacterial biomass was hydrolyzed using a simple enzymatic treatment and fermented to ethanol in higher concentrations and more rapidly than previously reported in similar approaches using cyanobacteria or microalgae. Importantly, besides fermentable carbohydrates the cyanobacterial hydrolysate contained additional nutrients that promoted fermentation by the yeast. This hydrolysate is therefore a promising substitute for the relatively expensive nutrient additives (such as yeast extract) commonly used for Saccharomyces fermentations.