PRODUCTION OF ETHANOL FROM LIGNOCELLULOSIC

Production Of Ethanol From Lignocellulosic Hydrolysate From Engineered Saccharomyces Cerevisiae Yeast

Production Of Ethanol From Lignocellulosic Hydrolysate From Engineered Saccharomyces Cerevisiae Yeast

1.how will you modify metabolic pathways of s.cerevisiae to perform reaction stated with optimal efficiency?describe how this will be done at the DNA level and what effect this will have at the proteome and metabolic levels.note that heterologous genes will need to be added to s.cerervisiae to perform the reaction but you must also address how central carbon metabolism will be optimized.

Extractive lactic acid fermentation has recently been paid a great deal of attention. The problem with such a process is, however, that only undissociated lactate can be extracted. Therefore, lactic acid fermentation at low pH values is desirable. In the present study, we modified the metabolism of yeast (not lactic acid producing bacteria often cultivated at pH of 6-7) by expressing the lactate dehydrogenase (LDH) gene for the production of lactate at low pH values. For this purpose, the plasmid pADNS which contains the ADH1 promoter is used as a host vector, and a heterologous gene region, cDNA-LDH-A (encoding bovine lactate dehydrogenase) digested from plasmid pLDH12 is digested and ligated into the aforementioned two host vectors. (Chundawat , 2007)

The resultant plasmids are then transformed into Saccharomyces cerevisiae DS37. Using this recombinant S. cerevisiae strain, several batch and fed-batch fermentations at aerobic, microaerobic, and anaerobic conditions are conducted at several pH values (4.5-3.5). Since the recombinant S. cerevisiae produced a considerable amount of ethanol as well as lactate (about 10 g/l), we disrupted several pyruvate decarboxylase (PDC) genes to suppress the ethanol formation. Among the PDC genes, PDC1, PDC5 and PDC6, PDC1 had the greatest effect on the cell growth and ethanol production. The plasmid which containing the LDH-A structure gene is then transformed into the mutant strain lacking the PDC1 gene. Cultivation of this strain improved the lactate yield from glucose (from 0.155 to 0.20) while suppressing ethanol formation (from 0.35 to 0.20). Cellulosic ethanol has been widely regarded as a promising alternative liquid fuel due to its projected positive attributes in terms of economic, environmental, and social sustainability(Chundawat , 2007). The ability to generate and convert fermentable sugars from lignocellulosic materials to ethanol in a cost-effective fashion is the central technological challenge to fully unlock its commercial potential . Unfortunately, fermentation of hydrolysates derived from pretreated lignocellulosic biomass is often preceded by washing, nutrient supplementation, and detoxification, which are very costly processes. The fermentability of a hydrolysate is strongly dependent on the feedstock pretreatment and strain selection. Improvements in these areas can significantly change the economic performance of fermentation using lignocellulosic biomass.

An experimental system for directing the evolution of enzymes and metabolic pathways in microbial populations is proposed and an initial test of its power is provided.-The test involved an attempt to genetically enhance certain functional properties of the enzyme acid phosphatase in S. cerevisiae by constructing an environment in which the functional changes desired would be ...