Search

A previously published genome‐scale metabolic model namely iFF708 was modified to depict the metabolic flux distribution within Saccharomyces cerevisiae grown under a redox potential–controlled very high‐gravity condition. The following modifications were made: electron transport chain (ETC) and oxidative phosphorylation, proton gradient and ATP transportation, and malate–aspartate shuttle. With these modifications, this model could describe the experimental data collected from the above‐mentioned ethanol fermentation. As a result, the simulation unveiled that the P/O ratio is critical under microaerobic conditions and the malate–aspartate shuttle is inactivated due to the shortage of electron transport across mitochondria. In other words, the limited supply of oxygen suppresses the functionality of oxidative phosphorylation, tricarboxylic acid (TCA) cycle, and ETC. In terms of the glycolytic pathway, fluxes coming from glucose‐6‐phosphate and pyruvate nodes are insensitive to the changes of fermentation redox potential. As the initial glucose concentration is greater than 250 g/L, the interactive effect between the initial glucose concentration and redox potential level becomes noticeable. [ABSTRACT FROM AUTHOR]

This study evaluated ethanol fermentation and its correlation with glutathione (GSH) synthesis under various cadmium-conditions with different metal ions and nitrogen sources. We found that corn steep liquor (CSL) and yeast extract have differential roles to play in GSH accumulation in cell even though both of them could alleviate the inhibition by cadmium. The different GSH accumulation in cell resulted from the different contents of metal ions in CSL and yeast extract. Intracellular GSH decreased with increasing calcium concentrations, and high calcium concentrations rendered the yeast more tolerant to cadmium stress than the nitrogen sources did. When the mole ratio of calcium to cadmium was 100:1, yeast tolerated 1000 mmol/L cadmium with no decrease in efficiency in ethanol production. As a result, the use of calcium allowed a significant saving of high-cost nutrient yeast extract with an efficient ethanol production, making the bioconversion of cadmium-containing biomass into ethanol possible. [ABSTRACT FROM AUTHOR]

Engineering industrial microbial strains with inulinase production for developing a consolidated bioprocessing (CBP) strategy is a desirable solution to biofuel production from Jerusalem artichoke tubers. In this study, the integrative vector pFA6a-rDNA-PGK-INU was generated by fusing the 3.3-kb ribosomal DNA fragment with the phosphoglycerate kinase promoter to regulate the expression of the inulinase gene isolated from Kluyveromyces marxianus, which was then integrated into the chromosome of an industrial Saccharomyces cerevisiae strain for ethanol production from Jerusalem artichoke tubers. Compared to the host strain, no significant difference was observed in the growth of the recombinant yeast, but its inulinase production was enhanced: 22.9 versus 10.6 U/mL for aerobic seed cultures and 14.5 versus 10.0 U/mL for ethanol fermentation, which consequently facilitated the CBP process for ethanol production: 72.5 g/L ethanol produced in a fermentation time of 48 h, while only 67.0 g/L ethanol was produced by the host strain in a fermentation time of 60 h. Thus, the ethanol productivity was increased from 1.12 to 1.51 g/L/h, presenting an increase of 34.8%. [ABSTRACT FROM AUTHOR]