Large-scale screening for multi-stress tolerant yeast strains for bioethanol production

Second generation bioethanol production using lignocellulosic agricultural residues like wheat and rice straw, corn stover, sugarcane bagasse etc. necessitates the introduction of very high gravity (VHG) fermentation technology under undefined, potentially harsh conditions. However, industrial application of VHG technology in bioethanol production is often limited by the unavailability of a fermentative microorganism resistant to the wide variety of stressors commonly encountered in such fermentation. In addition, the appropriate tools and knowledge to select such multi-stress tolerant microorganisms and to make a scientifically proven choice of the appropriate candidate strains have been lacking until recently. In this study,a large yeast culture collection, consisting of about 700 Saccharomyces cerevisiaeand non-Saccharomyces strains from diverse origins, is screened in view of bioethanol production. The strains tolerance against, osmotic pressure, , halotolerance, ethanol concentration, temperature, and fermentation inhibitors like furfural and hydroxymethyl furfural as well as some heavy metals are studied. A high throughput semi-automated robot is used for spotting up to 96 strains per screening plate. After incubation, plates are scanned and growth is recorded and analyzed using dedicated software. The top candidate species as well as top strain for each species and for each desirable trait have been successfully identified. Cluster analysis shows clear differences in tolerance among species and among strains of the same species. In addition, strains showing co-tolerance against different traits are identified.status: publishe