Isolation and identification of new yeast strains for the production of bioethanol from lignocellulose

In recent years increasing attention has been devoted to the production of bioethanol from lignocellulose, as cheap and abundant feedstock. The process requires a pretreatment of biomass, which may involve the formation of inhibitory compounds. Many works report on ethanol production from biomass hydrolysates, but only few focus on the selection of yeasts able to both tolerate inhibitors and ferment with high yield. In this work an isolation program from oenological environments (grape marcs) started in order to select new yeasts for the fermentation of lignocellulosic hydrolysates. Marcs were incubated with or without a cocktail of inhibitors at 30 and 40°C. At regular intervals marcs were collected and, after appropriate decimal dilutions, plated on agar dishes with and without inhibitors. More than 500 strains were isolated and genetically identified by ITS (Internal Transcribed Spacer) sequencing. Much effort was spent to identify yeasts belonging to Saccharomyces cerevisae, the most promising candidate for bioethanol production. S. cerevisiae strains were screened for their ability to grow in industrial medium containing increasing inhibitors concentrations and few isolates showed high tolerance to organic acids and furans. This study will allow the selection of few yeast strains suitable for the production of bioethanol from different types of lignocellulosic hydrolysates. The inhibitors tolerance of selected yeasts may be further increased by molecular biology techniques.