Screening and selection of yeast isolates capable of xylose catabolism, from natural and agricultural environments in Mexico

Bioethanol constitutes a very important alternative to ethers as an additive for gasoline in heavily polluted and populated areas of Mexico. So far, only MTBE and ETBE are used as gas carburant. In order to make use of the vast by-products from the sugarcane, maize and other agro-industries, it is important to develop biotechnologies based on xylose fermenting microorganisms, which could convert entirely hexoses and pentoses from lignocellulose hydrolysates, into ethanol. More than 230 yeast cultures from agave juices, natural and introduced grasses, fruit juices and forestry and agro-industrial by-products, were isolated and tested for their ability to grow in xylose as the only carbon source, and subsequently for their ability to grow and ferment xylose in both minimal (Wickerham defined medium) and complex media (MDS-YM). Selected strains were tested for their ability to produce ethanol in the presence or xylose, mannose, arabinose, glucose, or mixtures of glucose with each pentose sugar. Two strains have a strong potential to be used as bioethanol producers from lignocellulose hydrolysates.