Hybridization and adaptive evolution of diverse Saccharomyces species for cellulosic biofuel production

PERIS, DAVID; MORIARTY, RYAN V.; ALEXANDER, WILLIAM G.; BAKER, EMILYCLARE; SYLVESTER, KAYLA; SARDI, MARIA; LANGDON, QUINN K.; LIBKIND, DIEGO; WANG, QI-MING; BAI, FENG-YAN; LEDUCQ, JEAN-BAPTISTE; CHARRON, GUILLAUME; LANDRY, CHRISTIAN R.; SAMPAIO, JOSÉ PAULO; GONÇALVES, PAULA; HYMA, KATIE E.; FAY, JUSTIN C.; SATO, TREY K.; HITTINGER, CHRIS TODD

BIOTECHNOLOGY FOR BIOFUELS

BIOMED CENTRAL LTD

Año: 2017 vol. 10 p. 1 - 19

1754-6834

Background: Lignocellulosic biomass is a common resource across the globe, and its fermentation offers a prom‑ising option for generating renewable liquid transportation fuels. The deconstruction of lignocellulosic biomassreleases sugars that can be fermented by microbes, but these processes also produce fermentation inhibitors, suchas aromatic acids and aldehydes. Several research projects have investigated lignocellulosic biomass fermentation bythe baker?s yeast Saccharomyces cerevisiae. Most projects have taken synthetic biological approaches or have explorednaturally occurring diversity in S. cerevisiae to enhance stress tolerance, xylose consumption, or ethanol production.Despite these efforts, improved strains with new properties are needed. In other industrial processes, such as wineand beer fermentation, interspecies hybrids have combined important traits from multiple species, suggesting thatinterspecies hybridization may also offer potential for biofuel research.Results: To investigate the efficacy of this approach for traits relevant to lignocellulosic biofuel production, we gener‑ated synthetic hybrids by crossing engineered xylose-fermenting strains of S. cerevisiae with wild strains from variousSaccharomyces species. These interspecies hybrids retained important parental traits, such as xylose consumptionand stress tolerance, while displaying intermediate kinetic parameters and, in some cases, heterosis (hybrid vigor).Next, we exposed them to adaptive evolution in ammonia fiber expansion-pretreated corn stover hydrolysate andrecovered strains with improved fermentative traits. Genome sequencing showed that the genomes of these evolvedsynthetic hybrids underwent rearrangements, duplications, and deletions. To determine whether the genus Saccharomycescontains additional untapped potential, we screened a genetically diverse collection of more than 500 wild,non-engineered Saccharomyces isolates and uncovered a wide range of capabilities for traits relevant to cellulosicbiofuel production. Notably, Saccharomyces mikatae strains have high innate tolerance to hydrolysate toxins, whilesome Saccharomyces species have a robust native capacity to consume xylose.Conclusions: This research demonstrates that hybridization is a viable method to combine industrially relevant traitsfrom diverse yeast species and that members of the genus Saccharomyces beyond S. cerevisiae may offer advanta‑geous genes and traits of interest to the lignocellulosic biofuel industry.