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Ethanol Synthesis (ethanol + synthesis)
Selected AbstractsEthanol synthesis from glycerol by Escherichia coli redox mutants expressing adhE from Leuconostoc mesenteroidesJOURNAL OF APPLIED MICROBIOLOGY, Issue 2 2010P.I. Nikel Abstract Aims:, Analysis of the physiology and metabolism of Escherichia coli arcA and creC mutants expressing a bifunctional alcohol-acetaldehyde dehydrogenase from Leuconostoc mesenteroides growing on glycerol under oxygen-restricted conditions. The effect of an ldhA mutation and different growth medium modifications was also assessed. Methods and Results:, Expression of adhE in E. coli CT1061 [arcA creC(Con)] resulted in a 1·4-fold enhancement in ethanol synthesis. Significant amounts of lactate were produced during micro-oxic cultures and strain CT1061LE, in which fermentative lactate dehydrogenase was deleted, produced up to 6·5 ± 0·3 g l,1 ethanol in 48 h. Escherichia coli CT1061LE derivatives resistant to >25 g l,1 ethanol were obtained by metabolic evolution. Pyruvate and acetaldehyde addition significantly increased both biomass and ethanol concentrations, probably by overcoming acetyl-coenzyme A (CoA) shortage. Yeast extract also promoted growth and ethanol synthesis, and this positive effect was mainly attributable to its vitamin content. Two-stage bioreactor cultures were conducted in a minimal medium containing 100 ,g l,1 calcium d -pantothenate to evaluate oxic acetyl-CoA synthesis followed by a switch into fermentative conditions. Ethanol reached 15·4 ± 0·9 g l,1 with a volumetric productivity of 0·34 ± 0·02 g l,1 h,1. Conclusions:,Escherichia coli responded to adhE over-expression by funnelling carbon and reducing equivalents into a highly reduced metabolite, ethanol. Acetyl-CoA played a key role in micro-oxic ethanol synthesis and growth. Significance and Impact of the Study:, Insight into the micro-oxic metabolism of E. coli growing on glycerol is essential for the development of efficient industrial processes for reduced biochemicals production from this substrate, with special relevance to biofuels synthesis. [source] Characteristics of Saccharomyces cerevisiae gal1, and gal1,hxk2, mutants expressing recombinant proteins from the GAL promoterBIOTECHNOLOGY & BIOENGINEERING, Issue 6 2005Hyun Ah Kang Abstract Galactose can be used not only as an inducer of the GAL promoters, but also as a carbon source by Saccharomyces cerevisiae, which makes recombinant fermentation processes that use GAL promoters complicated and expensive. To overcome this problem during the cultivation of the recombinant strain expressing human serum albumin (HSA) from the GAL10 promoter, a gal1, mutant strain was constructed and its induction kinetics investigated. As expected, the gal1, strain did not use galactose, and showed high levels of HSA expression, even at extremely low galactose concentrations (0.05,0.1 g/L). However, the gal1, strain produced much more ethanol, in a complex medium containing glucose, than the GAL1 strain. To improve the physiological properties of the gal1, mutant strain as a host for heterologous protein production, a null mutation of either MIG1 or HXK2 was introduced into the gal1, mutant strain, generating gal1,mig1, and gal1,hxk2, double strains. The gal1,hxk2, strain showed a decreased rate of ethanol synthesis, with an accelerated rate of ethanol consumption, compared to the gal1, strain, whereas the gal1,mig1, strain showed similar patterns to the gal1, strain. Furthermore, the gal1,hxk2, strain secreted much more recombinant proteins (HSA and HSA fusion proteins) than the other strains. The results suggest that the gal1,hxk2, strain would be useful for the large-scale production of heterologous proteins from the GAL10 promoter in S. cerevisiae. © 2005 Wiley Periodicals, Inc. [source] | ||||||||||