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Recombinant Saccharomyces Cerevisiae (recombinant + saccharomyces_cerevisiae)
Selected AbstractsProduction of ,-galactosidase from recombinant Saccharomyces cerevisiae grown on lactoseJOURNAL OF CHEMICAL TECHNOLOGY & BIOTECHNOLOGY, Issue 8 2004Lucília Domingues Abstract Improved productivity and costs reduction in fermentation processes may be attained by using flocculating cell cultures. The production of extracellular heterologous ,-galactosidase by recombinant flocculating Saccharomyces cerevisiae cells, expressing the lacA gene (coding for ,-galactosidase) of Aspergillus niger under the ADHI promotor and terminator in a bioreactor was studied. The effects of lactose concentration and yeast extract concentration on ,-galactosidase production in a semi-synthetic medium were analysed. The extracellular ,-galactosidase activity increased linearly with increasing initial lactose concentrations (5,150 g dm,3). ,-Galactosidase production also increased with increased yeast extract concentration. During the entire fermentation, no accumulation of the hydrolysed sugars, glucose and galactose, was observed. The catabolic repression of the recombinant strain when cultured in a medium containing equal amounts of glucose and galactose was confirmed. In complete anaerobiosis, the fermentation of lactose resulted in a very slow fermentation pattern with lower levels of ,-galactosidase activity. The bioreactor operation together with optimisation of culture conditions (lactose and yeast extract concentration) led to a 21-fold increase in the extracellular ,-galactosidase activity produced when compared with preliminary Erlenmeyer fermentations. Copyright © 2004 Society of Chemical Industry [source] Effect of the reversal of coenzyme specificity by expression of mutated Pichia stipitis xylitol dehydrogenase in recombinant Saccharomyces cerevisiaeLETTERS IN APPLIED MICROBIOLOGY, Issue 2 2007J. Hou Abstract Aims:, To determine the effects on xylitol accumulation and ethanol yield of expression of mutated Pichia stipitis xylitol dehydrogenase (XDH) with reversal of coenzyme specificity in recombinant Saccharomyces cerevisiae. Methods and Results:, The genes XYL2 (D207A/I208R/F209S) and XYL2 (S96C/S99C/Y102C/D207A/I208R/F209S) were introduced into S. cerevisiae, which already contained the P. stipitis XYL1 gene (encoding xylose reductase, XR) and the endogenously overexpressed XKS1 gene (encoding xylulokinase, XK). The specific activities of mutated XDH in both strains showed a distinct increase in NADP+ -dependent activity in both strains with mutated XDH, reaching 0·782 and 0·698 U mg,1. In xylose fermentation, the strain with XDH (D207A/I208R/F209S) had a large decrease in xylitol and glycerol yield, while the xylose consumption and ethanol yield were decreased. In the strain with XDH (S96C/S99C/Y102C/D207A/I208R/F209S), the xylose consumption and ethanol yield were also decreased, and the xylitol yield was increased, because of low XDH activity. Conclusions:, Changing XDH coenzyme specificity was a sufficient method for reducing the production of xylitol, but high activity of XDH was also required for improved ethanol formation. Significance and Impact of the Study:, The difference in coenzyme specificity was a vital parameter controlling ethanolic xylose fermentation but the XDH/XR ratio was also important. [source] Alkali-based AFEX pretreatment for the conversion of sugarcane bagasse and cane leaf residues to ethanolBIOTECHNOLOGY & BIOENGINEERING, Issue 3 2010Chandraraj Krishnan Abstract Sugarcane is one of the major agricultural crops cultivated in tropical climate regions of the world. Each tonne of raw cane production is associated with the generation of 130,kg dry weight of bagasse after juice extraction and 250,kg dry weight of cane leaf residue postharvest. The annual world production of sugarcane is ,1.6 billion tones, generating 279 MMT tones of biomass residues (bagasse and cane leaf matter) that would be available for cellulosic ethanol production. Here, we investigated the production of cellulosic ethanol from sugar cane bagasse and sugar cane leaf residue using an alkaline pretreatment: ammonia fiber expansion (AFEX). The AFEX pretreatment improved the accessibility of cellulose and hemicelluloses to enzymes during hydrolysis by breaking down the ester linkages and other lignin carbohydrate complex (LCC) bonds and the sugar produced by this process is found to be highly fermentable. The maximum glucan conversion of AFEX pretreated bagasse and cane leaf residue by cellulases was ,85%. Supplementation with hemicellulases during enzymatic hydrolysis improved the xylan conversion up to 95,98%. Xylanase supplementation also contributed to a marginal improvement in the glucan conversion. AFEX-treated cane leaf residue was found to have a greater enzymatic digestibility compared to AFEX-treated bagasse. Co-fermentation of glucose and xylose, produced from high solid loading (6% glucan) hydrolysis of AFEX-treated bagasse and cane leaf residue, using the recombinant Saccharomyces cerevisiae (424A LNH-ST) produced 34,36,g/L of ethanol with 92% theoretical yield. These results demonstrate that AFEX pretreatment is a viable process for conversion of bagasse and cane leaf residue into cellulosic ethanol. Biotechnol. Bioeng. 2010;107: 441,450. © 2010 Wiley Periodicals, Inc. [source] | ||||||||||