Cellulosic biofuel production using emulsified simultaneous saccharification and fermentation (eSSF) with conventional and thermotolerant yeasts

Journal Article · Sat Jul 17 00:00:00 EDT 2021 · Biotechnology for Biofuels

DOI:https://doi.org/10.1186/s13068-021-02008-7· OSTI ID:1808610

Hoffman, Shannon M.; Alvarez, Maria; Alfassi, Gilad; Rein, Dmitry M.; Garcia-Echauri, Sergio; Cohen, Yachin; Avalos, José L.

Abstract Background Future expansion of corn-derived ethanol raises concerns of sustainability and competition with the food industry. Therefore, cellulosic biofuels derived from agricultural waste and dedicated energy crops are necessary. To date, slow and incomplete saccharification as well as high enzyme costs have hindered the economic viability of cellulosic biofuels, and while approaches like simultaneous saccharification and fermentation (SSF) and the use of thermotolerant microorganisms can enhance production, further improvements are needed. Cellulosic emulsions have been shown to enhance saccharification by increasing enzyme contact with cellulose fibers. In this study, we use these emulsions to develop an emulsified SSF (eSSF) process for rapid and efficient cellulosic biofuel production and make a direct three-way comparison of ethanol production between S. cerevisiae , O. polymorpha , and K. marxianus in glucose and cellulosic media at different temperatures. Results In this work, we show that cellulosic emulsions hydrolyze rapidly at temperatures tolerable to yeast, reaching up to 40-fold higher conversion in the first hour compared to microcrystalline cellulose (MCC). To evaluate suitable conditions for the eSSF process, we explored the upper temperature limits for the thermotolerant yeasts Kluyveromyces marxianus and Ogataea polymorpha , as well as Saccharomyces cerevisiae , and observed robust fermentation at up to 46, 50, and 42 °C for each yeast, respectively. We show that the eSSF process reaches high ethanol titers in short processing times, and produces close to theoretical yields at temperatures as low as 30 °C. Finally, we demonstrate the transferability of the eSSF technology to other products by producing the advanced biofuel isobutanol in a light-controlled eSSF using optogenetic regulators, resulting in up to fourfold higher titers relative to MCC SSF. Conclusions The eSSF process addresses the main challenges of cellulosic biofuel production by increasing saccharification rate at temperatures tolerable to yeast. The rapid hydrolysis of these emulsions at low temperatures permits fermentation using non-thermotolerant yeasts, short processing times, low enzyme loads, and makes it possible to extend the process to chemicals other than ethanol, such as isobutanol. This transferability establishes the eSSF process as a platform for the sustainable production of biofuels and chemicals as a whole.

• Research Organization: Princeton Univ., NJ (United States)
• Sponsoring Organization: USDOE Office of Science (SC), Biological and Environmental Research (BER); National Science Foundation (NSF); Israel Science Foundation (ISF); Xunta de Galicia
• Grant/Contract Number: SC0019363; CBET‑1751840; 123/18; ED481B‑2016/140‑0; ED481D‑2019/017)
• OSTI ID: 1808610
• Alternate ID(s): OSTI ID: 1853122
• Journal Information: Biotechnology for Biofuels, Journal Name: Biotechnology for Biofuels Vol. 14 Journal Issue: 1; ISSN 1754-6834
• Publisher: Springer Science + Business Media
• Country of Publication: Netherlands
• Language: English

Related Subjects

09 BIOMASS FUELS
59 BASIC BIOLOGICAL SCIENCES
Biotechnology & Applied Microbiology
Energy & Fuels
Cellulose
Biofuels
Emulsions
Ethanol
Isobutanol
SSF
Thermotolerant
Optogenetics
Biomass pretreatment
Saccharomyces cerevisiae
Ogataea polymorpha
Kluyveromyces marxianus