Super tolerant marine yeast for bioethanol production using seawater-based media

The total amount of freshwater required to produce 1L of bioethanol is currently around 200-300L. With biofuels projected to increase as a transportation fuel, there are concerns over use of freshwater resources with potential negative impacts on food production. Seawater -which is almost free and accounts for about 97% of the world’s water- can be a promising alternative especially in arid zones where freshwater is increasingly precious [1]. Therefore, the development of seawater-based media could make a significant impact on overcoming both freshwater shortage and the energy crisis. This paper describes a newly isolated marine yeast strain -identified as Sccharomyces cereviae- that was able to ferment high levels of glucose (up to 30%) in the presence of high salts (up to 9%, mainly NaCl). The reference strain S. cereviae NCYC2592 was used for comparison and the marine strain showed significant superiority in ethanol productivity and tolerance to glucose and salt. This osmo-halotolerant yeast strain was used in a 15L bioreactor at 0.5OD initial inoculum level to ferment 25% (w/v)  sugarcane molasses (about 12% sugars) in natural seawater (about 3.5% salts) with addition of 0.1% (w/v) urea and shown to produce 48.44g/L (w/v) of ethanol in 34h at 30^oC. These findings highlight the potential of marine yeasts and seawater-based media in bioethanol production. They also provide a new strategy for increasing the efficiency of bioethanol production at the industrial level with positive impact on food and freshwater scarcity issue.

[1]Zaky et.al. (2014) Marine Yeast Isolation and Industrial Application. FEMS Yeast Research