Production of xylose enriched hydrolysate from bioenergy sorghum and its conversion to ß-carotene using an engineered Saccharomyces cerevisiae

Authors: CHENG, MING-HSUN - University Of Illinois; SUN, LIANG - University Of Illinois; JIN, YONG-SU - University Of Illinois; Dien, Bruce; SINGH, VIJAY - University Of Illinois

Submitted to: Bioresource Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/1/2020
Publication Date: 3/31/2020
Citation: Cheng, M., Sun, L., Jin, Y., Dien, B.S., Singh, V. 2020. Production of xylose enriched hydrolysate from bioenergy sorghum and its conversion to ß-carotene using an engineered Saccharomyces cerevisiae. Bioresource Technology. 308. Article 123275. https://doi.org/10.1016/j.biortech.2020.123275.
DOI: https://doi.org/10.1016/j.biortech.2020.123275

Interpretive Summary: An economic obstacle to producing cellulosic biofuels is the low market price of bioethanol relative to its operating and very high capital costs. This work addresses this point in two ways. First, a novel two-stage pretreatment has been developed that consists of hot-water pretreatment followed by disc refining. This has been scaled up using a continuous steam pretreatment reactor. Hot-water is advantageous because it only uses heated water as the catalyst and disc milling allows for commercial attractive sugar yields following enzymatic hydrolysis. This process has been expanded to allow for generation of a co-product from the less desirable (for biofuel fermentation) xylose fraction. The xylose syrup was recovered following pretreatment and concentrated to achieve 66 grams of xylose per liter. The concentrated syrup was next used for production of value-added ß-carotene using an engineered S. cerevisiae. The maximum product titer was 114.5 mg/L. To summarize a commercially attractive process of generating sugars from biomass was used to produce an enriched xylose syrup and these sugars used to product a value-added product. This research will be of interest to those work on commercializing cellulosic biofuels and more generally agriculturally based refiners.

Technical Abstract: A new bioprocess has been developed that allows for producing ß-carotene from the xylose portion of bioenergy sorghum. Bioenergy sorghum was pretreated in a pilot-scale continuous hydrothermal reactor followed by disc refining. Xylose was extracted using low-severity dilute acid hydrolysis. A xylose yield of 64.9% (17.4 g/L) was obtained by hydrolyzing at 120°C for 5 min with 2% sulfuric acid. The xylose-enriched syrup was separated and concentrated to either 32 g xylose/L (medium concentrated hydrolysate, MCB) or 66 g xylose/L (high-concentrated hydrolysate, HCB). The non- (NCB), medium-, and high-concentrated xylose syrup were neutralized and fermented to ß-carotene using Saccharomyces cerevisiae strain SR8B, which had been engineered for xylose utilization and ß-carotene production. In HCB, MCB, and NCB cultures, the yeast produced ß-carotene titers of 114.50 mg/L, 93.56 mg/L, and 82.50 mg/L, which corresponds to specific yeast biomass production of 7.32 mg/g DCW, 8.10 mg/g DCW, and 8.29 mg/g DCW, respectively.