Ethanol Production With Inulin As Carbon Source By Saccharomyces Cerevisiae

With the progress and development of the times, faced with the dilemma of depleting fossil fuels and environmental pollution treatment, the obligations of reducing carbon emissions presented by "Kyoto Protocol" for countries are also of concern and the situation of energy supply in the global is increasingly grim. Therefore finding efficient and clean energy has become impending research direction around the whole mankind. Due to clean, non-polluting, sustainable, renewable and other advantages in the field of energy, bio-ethanol has gained popularity,becoming a very promising biomass energy. The rational development and utilization of bio-ethanol have become the focus of the world’s energy sector.Faced with the situation of people more and food less, and in consideration of the economic and environmental friendliness, our country needs urgently develop a fuel ethanol production route based on "non-food substances". Jerusalem artichoke is easy to grow and low-cost, as well as a good sugar source for ethanol production through microbial fermentation, with great development value, whose underground tubers are rich in inulin. In recent years, researchers have screened successively several Saccharomyces cerevisiaes using inulin directly from nature. It has been reported that invertase is a key enzyme involved in inulin degradation in S.cerevisiaes,and SUC2 is the key encoding genes. Inulin fermentation is a key technology of industrial production for preparing bioethanols by the use of biological raw materials.In this paper, the process of inulin fermentation in S.cerevisiaes for ethanol production was studied. We took S.cerevisiaes BY4741, wild type L610 and recombinant strains as research object, and inulin was fermented to produce ethanol,respectively. By optimizing the promoters of SUC2 genes, the recombinant strains of S.cerevisiaes of different expression levels could be obtained. Then we conducted ethanol fermentation experiments, investigating the effects of different expression levels of SUC2 genes of inulinase activity,consequently further explored the relationship between inulinase activity and ethanol production.This paper analyzes the cases of S.cerevisiaes BY4741 using different substrates and researches the effect of different substrate concentration on ethanol performance of S.cerevisiaes BY4741, as well as confirms that S.cerevisiaes can utilize high concentrations of fructose, glucose and sucrose as substrates continuously for ethanol production via fermentation.By selecting different SUC2 genes of low, medium and high expression levels in S.cerevisiaes for ethanol fermentation research,the results confirm that the size of biomass of the recombinant bacteria has nothing to do with the levels of gene expression.The S.cerevisiaes with a medium level of SUC2 enzyme has the strongest ability of producing ethanol, due to an invertase, a key enzyme encoded by SUC2 genes in S.cerevisiaes during the ethanol production by the fermentation of inulin.The invertase activity is proportional to the ethanol production, therefore increasing the invertase activity of S.cerevisiaes contributes to improve ethanol production. The conditions of medium expression level of recombinant strains producing ethanol by the fermentation of inulin are optimized. The conditions are the temperature of 37 oC and pH 5.5, which are conducive to increase the activity of S.cerevisiaes. So relatively high inulin utilization and ethanol production can be obtained. Research results of this subject lay the foundations for the realization of the transformation of the enzyme genes by genetic engineering, finding the optimal expression level, thereby increasing the strain performance of ethanol production, and the investment in large-scale industrial production.