Buffalo rumen harbours diverse thermotolerant yeasts capable of producing second-generation bioethanol from lignocellulosic biomass

Abstract

High-temperature ethanol production from lignocellulosic biomass through simultaneous saccharification and fermentation (SSF) is preferred for the sustainable and cost-effective production of second-generation bioethanol, and SSF requires efficient thermotolerant yeasts. In this study, 101 thermotolerant yeasts were isolated from the buffalo rumen; among selected 48 yeasts, 31 grew at 45 °C, and 17 yeasts could utilise multiple sugars. At 40, 42 and 45 °C, C. glabrata RGB2.2, P. kudriavzevii RGB3.2, K. marxianus RGB4.5, C. tropicalis RGB5.6, and C. nivariensis RGB7.5 strains showed high ethanol concentrations of 4.5–4.9, 4.4–4.8, 3.9–4.2 g/L respectively, with the fermentation efficiency of 78%–95%, 87%–94%, 77%–83%, respectively, in fermentation medium with 1% glucose. Among these yeasts, P. kudriavzevii RGB3.2 and C. glabrata RGB2.2 exhibited significant tolerance towards furfural, 5-HMF, acetic acid, and ethanol. These two strains can produce 9.1 and 9 g/L ethanol, respectively, at 45 °C with a fermentation efficiency of 86.7% and 86%, respectively, through the SSF of alkali-treated rice straw. Therefore, the buffalo rumen can be a potential niche for inhibitor tolerant, multiple sugar-utilising, ethanologenic, thermotolerant yeasts suitable for SSF approach.