Fermentation profiles of the yeast Brettanomyces bruxellensis in D-xylose and L-arabinose aiming its application as a second-generation ethanol producer.

The yeast Brettanomyces bruxellensisis able to ferment the main sugars used in first-generation ethanol production. However, its employment in this industry is prohibitive because the ethanol productivity reached is significantly lower than the observed for Saccharomyces cerevisiae. On the other hand, a possible application of B. bruxellensisin the second-generation ethanol production has been suggested because this yeast is also able to used-xylose and L-arabinose, the major pentoses released from lignocellulosic material. Although the latter application seems to be reasonable, it has been poorly explored. Therefore, we aimed to evaluate whether or not different industrial strains of B. bruxellensisare able to ferment D-xylose and L-arabinose, both in aerobiosis and oxygen-limited conditions. Three out of nine tested strains were able to assimilate those sugars. When in aerobiosis,B. bruxellensiscells exclusively used them to support biomass formation, and no ethanol was produced. Moreover, whereas L-arabinose was not consumed under oxygen limitation, D-xylose was only slightly used, which resulted in low ethanol yield and productivity. In conclusion, our results showed that D-xylose and L-arabinose are not efficiently converted to ethanol by B. bruxellensis, most likely due to a redox imbalance in the assimilatory pathways of these sugars. Therefore, despite presenting other industrially relevant traits, the employment of B. bruxellensisin second-generation ethanol production depends on the development of genetic engineering strategies to overcome this metabolic bottleneck.