Whole-cell hydrolysate of cyanobacteria enhances biofuel fermentation of plant biomass.

Biofuel fermentation of plant materials by yeast typically requires supplementation with nutrients, such as vitamins and nitrogenous compounds, to enable yeast metabolic activity and growth. In this study, we used a simple milliliter-scale fermentation vial system to demonstrate that hydrolyzed whole-cell biomass from a photosynthetic cyanobacterium (Synechococcus sp. PCC 7002) can be used as a nutrient supplement for yeast fermentation of wheat straw and spruce. Adding lysozyme-treated, high-nitrogen cyanobacterial biomass (0.5% dry matter, w/v) to a Saccharomyces cerevisiae fermentation of wheat straw hydrolysate (∼30% dry matter, w/w) increased the initial ethanol production rate from 6.7 ± 0.2 to 18.7 ± 1.0 g l-1 day-1, representing a nearly three-fold enhancement. Supplementation of an equivalent amount of acid-hydrolyzed cyanobacterial biomass increased ethanol production rates by only ~50%, indicating that essential nutrients were degraded during acid treatment. In addition, high-nitrogen cyanobacterial biomass improved initial ethanol production rates from wheat straw by 30%-80% compared to low-nitrogen biomass, suggesting that nitrogenous nutrients in the cyanobacteria were responsible for the enhanced yeast activity. Our data show that biomass from cyanobacteria can be used as a sustainable alternative to conventional nutrient supplements for biofuel fermentation of lignocellulosic biomass, including wheat straw and spruce hydrolysates.