Xylose assimilation enhances the production of isobutanol in engineered Saccharomyces cerevisiae

Abstract

Bioconversion of xylose—the second most abundant sugar in nature—into high‐value fuels and chemicals by engineered Saccharomyces cerevisiae has been a long‐term goal of the metabolic engineering community. Although most efforts have heavily focused on the production of ethanol by engineered S. cerevisiae, yields and productivities of ethanol produced from xylose have remained inferior as compared with ethanol produced from glucose. However, this entrenched focus on ethanol has concealed the fact that many aspects of xylose metabolism favor the production of nonethanol products. Through reduced overall metabolic flux, a more respiratory nature of consumption, and evading glucose signaling pathways, the bioconversion of xylose can be more amenable to redirecting flux away from ethanol towards the desired target product. In this report, we show that coupling xylose consumption via the oxidoreductive pathway with a mitochondrially‐targeted isobutanol biosynthesis pathway leads to enhanced product yields and titers as compared to cultures utilizing glucose or galactose as a carbon source. Through the optimization of culture conditions, we achieve 2.6 g/L of isobutanol in the fed‐batch flask and bioreactor fermentations. These results suggest that there may be synergistic benefits of coupling xylose assimilation with the production of nonethanol value‐added products.

Metabolic Engineering of Saccharomyces cerevisiae for Enhanced Carotenoid Production From Xylose-Glucose Mixtures

“…Meanwhile, we found that SC105 produced much lower carotenoid (20.2 mg L −1 ) when xylose was used as the sole carbon source than using mixed sugars (Figure 4). This result was different from that obtained in a previous work where the production yield from xylose shown remarkable improvement than that from glucose Lane et al, 2020). We also found that strains almost could not grow on YP medium without sugars (Figure 5A).…”

Co-Production of Isobutanol and Ethanol from Prairie Grain Starch Using Engineered Saccharomyces cerevisiae

“…Greater yields may also be possible when the yeast is engineered to effectively assimilate pentose sugars, which make up 1-2% of the sugars in the present in the mash. Some progress has been made on improving the conversion of xylose to isobutanol in S. cerevisiae but to date yields remain low and there has been no effective demonstration of the conversion of pentose sugars from a mixed carbon feedstock [9,42,43]. This may also open the possibility of using cellulosic and hemicellulosic materials as feedstock.…”

“…Most butanol and isobutanol are currently synthesized from petrochemicals, however, Clostridium acetobutylicum will naturally produce 1-butanol and Saccharomyces cerevisiae, bacteria and cyanobacteria have been engineered to produce these alcohols [4][5][6][7][8]. Isobutanol production by E. coli and S. cerevisiae has used glucose as feedstock but microbial strains have been engineered to achieve isobutanol synthesis from xylose, cellulose, methanol, cheese whey and acetate [9][10][11][12][13].…”

Xylose Assimilation for the Efficient Production of Biofuels and Chemicals by Engineered Saccharomyces cerevisiae

“…Similarly, Lane et al coupled the mitochondrial isobutanol biosynthetic pathway with xylose consumption via the XR-XDH pathway, leading to increased isobutanol yields and titers. [70] The resulting strain produced 2.6 g L −1 isobutanol using xylose as a carbon source in batch flask and bioreactor fermentations. Apart from the slow rates of sugar consumption, the enhanced levels of isobutanol or 2-methyl-1-butanol production in both studies were also attributed to the alleviation of glucose repression on mitochondrial biogenesis and function by xylose utilization.…”

“…[68] Apart from the diminished overflow metabolism, recent studies producing isobutanol in mitochondrion also attributed the improved production from xylose to the activation of mitochondrial biogenesis and activity, which was repressed by glucose. [69,70] Thus, more mitochondrion-targeted biosynthesis may benefit from xylose utilization.…”