Evaluation of performance of different surface-engineered yeast strains for direct ethanol production from raw starch

Abstract

Four types of cell-surface-engineered yeast Saccharomyces cerevisiae displaying glucoamylase, namely, systems A, B, C, and D, were constructed to evaluate their performance in direct ethanol fermentation from raw corn starch. Systems A and B were glucoamylase-displaying nonflocculent yeast (YF237) types that secrete alpha-amylase into the culture medium and codisplay alpha-amylase on the cell surface, respectively. Systems C and D were flocculent yeast counterparts (YF207) for systems A and B, respectively. In batch fermentations, the specific ethanol production rates of systems A, B, C, and D were 0.18, 0.06, 0.06, and 0.04 g (g cell)(-1) h(-1), respectively. In repeated fermentations, the specific ethanol production rate of system A decreased with the number of repetitions, whereas, that of system B was maintained. In all systems, the rate-limiting step was the conversion of starch to oligosaccharide because oligosaccharide and glucose were not accumulated throughout the fermentations.

Designing industrial yeasts for the consolidated bioprocessing of starchy biomass to ethanol

“…From soluble starch, the S. cerevisiae F2 and F6 produced high ethanol levels and their fermentative abilities were similar to those of previously engineered strains. 16,27,28 The conversion rate of starch to ethanol was found to be much more efficient in the case of S. cerevisiae F2 (data not shown). However, both recombinant yeasts were not able to metabolize all the starch available and the same result was observed from raw starch where the recombinants produced limited ethanol concentrations ( Table 2).…”

“…Laboratory strains are easily genetically modified and the functionality of starch hydrolyzing enzymes has been proved by various laboratories. 15,16 Episomal plasmid vectors under selection have been mainly utilized for the overexpression of target genes in laboratory S. cerevisiae strains to ensure high copy numbers (50-200 copies) are maintained. Despite these advantages, most industrial yeasts are much more robust than laboratory strains and display higher specific ethanol productivities and ethanol yields, producing a lower amount of undesirable by-products, like glycerol.…”

Progress in Metabolic Engineering of Saccharomyces cerevisiae

“…Engineers expressed glucoamylase either alone (177,303) or in combination with ␣-amylase (81,163,315) or even with pullulanase (136). Many approaches have relied on anchoring starch-degrading enzymes on the yeast cell surface using the Flo1 protein (163,177,303,315).…”

Cell surface display of highly pathogenic avian influenza virus hemagglutinin on the surface of Pichia pastoris cells using α‐agglutinin for production of oral vaccines

“…The C-terminus of a-agglutinin has been successfully used to display several foreign proteins such as a-amylase and red sea bream iridovirus 380R antigen on surface of S. cerevisiae. 7,8 More recently, the use of the methylotrophic yeast Pichia pastoris has been used to display enhanced green fluorescence protein (EGFP) and K. lactis yellow enzyme (KYE) using the a-agglutinin C-terminal anchoring method. Methanol-inducible P. pastoris expression vectors are also commercially available.…”