Adaptation of a flocculent Saccharomyces cerevisiae strain to lignocellulosic inhibitors by cell recycle batch fermentation

The ethanol production from lignocellulosic feedstocks is considered a promising strategy to increase global production of biofuels without impacting food supplies. However, some compounds released during the hydrolysis of lignocellulosic materials are toxic for the microbial metabolism, causing low ethanol yield and productivity during the fermentation. As an attempt to overcome this problem, the present study evaluated the adaptation of a flocculent strain of Saccharomyces cerevisiae (NRRL Y-265) to several inhibitory compounds usually found in lignocellulosic hydrolysates (acetic acid, furfural, hydroxymethylfurfural, vanillin, syringaldehyde, and hydroxybenzoic acid), aiming to minimize their negative effects on yeast metabolism, maximizing the ethanol production as a consequence. Cell recycle batch fermentation (CRBF) was performed during 39 consecutive days, using five different fermentation media with sequential increase in the concentration of inhibitory compounds, simulating the composition of lignocellulosic hydrolysates. This strategy allowed obtaining a yeast strain with increased ethanol volumetric productivity and growth rate (10% and 70% respectively, over parent strain) able to produce ethanol with better results when cultivated in glucose-supplemented steam-exploded eucalyptus hydrolysate.