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Biodegradation and Biocatalysis Aspects of Direct Bioethanol Production by Fungi in a Single Step Named Consolidated Bioprocessing
Published in Ayerim Y. Hernández Almanza, Nagamani Balagurusamy, Héctor Ruiz Leza, Cristóbal N. Aguilar, Bioethanol, 2023
Luis Fernando Amador Castro, Danay Carrillo Nieves
Once that lignocellulosic materials have been pretreated and lignocellulolytic enzymes have degraded the main components of the cell wall, sugars are fermented to produce ethanol [93]. Sugars derived from cellulose and hemicellulose degradation include hexoses such as glucose, mannose, fructose, and galactose, as well as pentoses, namely xylose and arabinose [94]. Some microorganisms like yeast, fungi, and bacteria possess the mechanisms for fermenting these sugars into ethanol; being yeasts the most studied and industrially-employed organisms [95]. Saccharomyces cerevisiae can natively ferment hexoses; fermentation of glucose, mannose, and fructose occurs via the Embden-Meyerhof pathway of glycolysis, and galactose fermentation via the Leloir pathway [93]. The Entner-Doudoroff (ED) pathway is an additional pathway that allows glucose fermentation bacteria such as Zymomonas [96]. However, the use of these species of bacteria may not be suitable for industrial bioethanol production as it can only ferment glucose, fructose, and sucrose [96]. Wildtype S. cerevisiae is not capable of fermenting neither xylose nor arabinose. But some species of Candida have been identified to ferment these substrates into ethanol [93]. Rhamnose, 6-deoxy sugar, can also be available for fermentation as it is a constituent of the rhamnogalacturonan part of pectin and hemicellulose. However, as its alcoholic fermentation pathway is not natively expressed in most organisms, metabolic engineering will be required to express a route for its fermentation in microorganisms that are currently used for industrial fermentation [93]. The use of genetic engineering can greatly increase the yield of bioethanol from LCB by allowing the engineered organism to ferment most of the available sugars. Furthermore, the integration of lignocellulosic enzymes will make able to develop a consolidated bioprocess to simultaneously perform the saccharification and fermentation processes.
Potential of “coalho” cheese whey as lactose source for β-galactosidase and ethanol co-production by Kluyveromyces spp. yeasts
Published in Preparative Biochemistry & Biotechnology, 2020
Catherine Teixeira de Carvalho, Sérgio Dantas de Oliveira Júnior, Wildson Bernardino de Brito Lima, Fábio Gonçalves Macêdo de Medeiros, Ana Laura Oliveira de Sá Leitão, Everaldo Silvino dos Santos, Gorete Ribeiro de Macedo, Francisco Caninde de Sousa Júnior
The genes LAC12 and LAC4 are found in the strain K. lactis NRRL Y-8279, and they are responsible for the codification of lactose-permease and ß-galactosidade enzymes, respectively, which play different roles in this process. Lactose-permease enzymes promote the lactose transport through the plasma membrane into the yeast cells, while the β-gal is responsible for the hydrolysis of lactose (disaccharide) into two monosaccharides, glucose and galactose. These two sugars are metabolized via glycolysis, however, before attending this metabolic route, galactose is converted into a glycolytic intermediate, the glucose-6-phosphate, via the Leloir pathway, by the action of three enzymes galactokinase, galactose-1-P-uridil transferase and UDP-galactose-4-epimerase.[39,40]