Screening by MALDI-TOF and characterization of newly identified xylose-fermenting yeasts

Xylose is the pentose sugar most abundant in nature and can account up to 30% of total sugar in some lignocellulosic biomasses, such as sugarcane bagasse. Thus, conversion of xylose to bioethanol and other chemicals is essential for biorefinery economics. Identification of new species of xylose-fermenting yeasts would allow increased ethanol production without increasing cultivated area. In this context, we developed a MALDI-TOF methodology for identification of yeasts capable of fermenting xylose. Initially, a protein profile database of xylose-consuming and xylose-fermenting yeasts was constructed using a MALDI-TOF based methodology. Following, wild yeasts isolated from Brazilian Savana were screened and grouped as xylose-consuming or xylose-fermenting. Xylose fermentation capability of three newly selected isolates (JA01, JA05 and JA09) was confirmed in synthetic medium. Scheffersomyces stipitis consumed 25 g.L^-1 of xylose and presented ethanol yield of 0.32 g.g^-1 in 47h of fermentation under oxygen-limited conditions, whereas the best isolates consumed up to 40 g.L^-1 of xylose and presented ethanol yields of  0.42 g.g^-1. Despite similar performance of JA01 and JA05 in synthetic medium, JA05 showed higher ethanol yields and productivity than JA01 on sugarcane bagasse hydrolysate. Sequencing of 26S rDNA demonstrated that JA01, JA05 and JA09 are close related to Spathaspora sp. and Candida materiae. Whole genome of JA01, JA05 and JA09 was sequenced and comparative genetics will help to better explain physiology of such yeasts. Our results demonstrated the potential of MALDI-TOF methodology for selection of xylose-fermenting yeasts with high ethanol production titers and yield in synthetic medium and sugarcane bagasse hydrolysate.