Simultaneous cell growth and ethanol production from cellulose by an engineered yeast consortium displaying a functional mini-cellulosome

Abstract

BackgroundThe recalcitrant nature of cellulosic materials and the high cost of enzymes required for efficient hydrolysis are the major impeding steps to their practical usage for ethanol production. Ideally, a recombinant microorganism, possessing the capability to utilize cellulose for simultaneous growth and ethanol production, is of great interest. We have reported recently the use of a yeast consortium for the functional presentation of a mini-cellulosome structure onto the yeast surface by exploiting the specific interaction of different cohesin-dockerin pairs. In this study, we engineered a yeast consortium capable of displaying a functional mini-cellulosome for the simultaneous growth and ethanol production on phosphoric acid swollen cellulose (PASC).ResultsA yeast consortium composed of four different populations was engineered to display a functional mini-cellulosome containing an endoglucanase, an exoglucanase and a β-glucosidase. The resulting consortium was demonstrated to utilize PASC for growth and ethanol production. The final ethanol production of 1.25 g/L corresponded to 87% of the theoretical value and was 3-fold higher than a similar yeast consortium secreting only the three cellulases. Quantitative PCR was used to enumerate the dynamics of each individual yeast population for the two consortia. Results indicated that the slight difference in cell growth cannot explain the 3-fold increase in PASC hydrolysis and ethanol production. Instead, the substantial increase in ethanol production is consistent with the reported synergistic effect on cellulose hydrolysis using the displayed mini-cellulosome.ConclusionsThis report represents a significant step towards the goal of cellulosic ethanol production. This engineered yeast consortium displaying a functional mini-cellulosome demonstrated not only the ability to grow on the released sugars from PASC but also a 3-fold higher ethanol production than a similar yeast consortium secreting only the three cellulases. The use of more complex cellulosomal structures may further improve the overall efficiency for ethanol production.

Self-surface assembly of cellulosomes with two miniscaffoldins on Saccharomyces cerevisiae for cellulosic ethanol production

“…Such an organization may explain why C. thermocellum is so efficient at hydrolyzing microcrystalline cellulose (17). During the past 2 y, several attempts have been reported to construct minicellulosomes with single scaffoldin on the S. cerevisiae surface (18)(19)(20)(21). The recombinant yeast has been able to hydrolyze β-glucan, carboxymethyl cellulose (CMC), or amorphous cellulose, and the activity of cellulosome was observed as higher than that of free cellulases.…”

Functional Display of Complex Cellulosomes on the Yeast Surface via Adaptive Assembly

“…On average, a detectable fluorescence signal was observed for around 70% of the cells after induction, consistent with other reports using the Aga1-Aga2 anchor system for surface display. 20,21,26 Expression of the Adapter Scaffoldins and Their Functional Docking onto the Anchoring Scaffoldin. The two adaptor scaffoldins were expressed in E. coli strain BL21 Gold under control of a strong T7 promoter.…”

Advances in consolidated bioprocessing systems for bioethanol and butanol production from biomass: a comprehensive review

“…This is probably due to the heavy metabolic burden and potential jamming of the secretion machinery. So, in other works, surface assembly of functional minicellulosome by using a synthetic yeast consortium has been reported (Tsai et al, 2010;Goyal et al, 2011). Tsai et al (2010) used a synthetic yeast consortium composed of four engineered strains, including one strain displaying a mini-scaffoldin carrying three different cohesin domains (SC), and three strains secreting dockerin-tagged cellulases (endoglucanase (AT), exoglucanase (CB) and β-glucosidase (BF)).The optimized consortium consisted of a SC:AT:CB:BF ratio of 7:2:4:2 and produced 1.87 g/l ethanol (ethanol yield of 0.475 g/g cellulose consumed, and 93% of the theoretical value).…”