As published in the 2024 European Congress on Biotechnology abstracts: Exploring yeast diversity for ethanol-fueled industrial biotechnology

Abstract

Ethanol is produced at industrial scale from non-agricultural feedstocks by gas fermentation, while research on other low-emission processes for ethanol production is accelerating. In view of its degree of reduction, water solubility and relatively low toxicity, ethanol is an interesting candidate to replace sugars in aerobic, zero-emission processes for yeast-based production of whole-cell protein and low-molecular-weight compounds. Currently, little information is available on specific growth rates, biomass yields and biomass composition of yeast species during growth on synthetic medium with ethanol as sole carbon source. In this study, strains of 52 Saccharomycotina yeasts were screened for their growth characteristics on ethanol. After first screening in microtiter plates, 21 fast-growing strains that were further analysed in aerobic shake-flask cultures showed specific growth rates of 0.12-0.46 h−1. Five fast-growing strains were further studied in aerobic, ethanol-limited chemostats (dilution rate 0.10 h−1). Strains of the industrial yeasts Saccharomyces cerevisiae and Kluyveromyces lactis, whose genomes lack genes for a proton-coupled Complex-I NADH dehydrogenase, both showed biomass yields of 0.6 g biomass (g ethanol)−1. Of three yeasts whose genome does contain Complex-I genes, Phaffomyces thermotolerans, showed the same biomass yield as S. cerevisiae, while Ogataea parapolymorpha and Cyberlindnera jadinii showed biomass yields of 0.67 ± 0.01 and 0.73 ± 0.00 g g−1, respectively. The biomass yield of C. jadinii, which also showed the highest protein content of the 5 yeasts tested in chemostats, corresponded to 88% of the theoretical biomass yield in a scenario where growth is limited by assimilation rather than by energy metabolism.