The Mechanism Of Sugar Accmulation And Metabolisimin Transfor Ming Process Of Sweet Sorghum To Ethanol

Sweet sorghum is one of the the non-agricultural plantsfor the development of second generation biomass energy. This thesis aims at the establishment ofindustrial production route for the conversion of sweet sorghum into ethanol.The relevant research is started with the investigation of sugar formation, accumulation and transformation into ethanol. The goals forthe growth conditions of sweet sorghum leading to high biomass production and sugar contents, forthe storage conditions with reduced sugar degradation, for the strain mutagenesis and screening ofthe genetically engineered hosts which allow fermentation of five-carbon sugars have been achievedfor thedebottlenecking the technical problems in the commercialization chain in the bioethanol industry. In conclusions:(1) Based on the correlation of biomass and sugar contents with given planting density, fertilization, sowing time and other environmental factors for sweet sorghum, total sugar, reducing sugar, sucrose and sucrose synthase and sucrose phosphate synthase under different growth stages of sweet sorghum are characterized for their variation within the contextof efficient metabolism. It was found that the sweet sorghum species in Xinjiang are of high biomass yield and sugar contents, if the cultivation process is optimized, further increase in biomass and sugar contents cann be expected.(2)Different stacking modes are studied for the changes in total sugar, reducing sugar, sucrose and sucrose synthase and sucrose phosphate synthase and sugar contents.It is found that vertical piling of sweet sorghum stalks result inless reduction of thesugar.(3)With multiple mutation, high ethanol producers from the yeast saccharomyces cerevisiae (including its mutagenesis strains) are obtained which are suitable for six-carbon sugar fermentation of sweet sorghum straws in xinjiang to produce ethanol with high yield.(4)From recombinant bacteria ATCC39676(PZB206), Hugh hatha Candida CBS2779, trunk pichia CBS7126,several genes, such as xylose reductase xyll, xylitol dehydrogenase xyl2, aldehyde enzyme tall, xylulose kinase xksl andxylulosetransketolase tkll are cloned to establish a serious multi-gene transformation vector to insert the above genes into the yeast cells. It isfound that this transformation vector for Saccharomyces cerevisiae is easy for separation, purification, post-translation modification (i.e., glycosylation and fold), etc. Although there still exist some issues such asprolongedcultivation period, complex operation conditions, limited protein expression and activity, it is convinced that but S. cerevisiaeis suitable for the co-fermentation of five-carbon sugar and six-carbon sugar for bioethanol production.Progress through the thesis research is summerised as follows:(1) Research on fermentation microbes:a:with the aid of genetic engineering, the constructs from Saccharomyces cerevisiae can convert five-carbon sugars into ethanol. b:with multiple mutagenesis, enhanced ethanol producers from S. cerevisiae (including its mutagenesis strain) is capable of fermentsix-carbon sugars from the sweet sorghum strawsin Xinjinag to efficiently produce ethanol. (2) By the research on glucose/xyloseco-fermentationfor ethanolproduction, it is found that with the increasing percentage of xylose in the fermentation broth, ethanol yield will decline gradually. In6%glucose medium, recombinant strains proliferate faster, with higher fermentation efficiency.At the fermentation time of48h, ethanol concentration is41.75mg/mL, and ethanol yield is78%. When G/X ratio is5:1, ethanol yield is the highest.At60h, ethanol concentration is41.88mg/mL, ethanol yield become76.92%,the sugar utilization rate is96.78%.(3) By correlation of biomass and sugar contetn of sweet sorghum, a, It is determined that the ecological conditions in Xinjiang, such as sufficient sunlight, rare rainfall, day/night temperature difference are in favor of biomass formation and increased sugar accumulation with photosynthesis.It can also be concluded that in order to improve the ethanol yield from sweet sorghum, it is feasible:a:to screen constructs to improve six-carbon sugar fermentation for ethanol production; b:to reduce the non-ethanol fermentation products; c:to construct strong strains for five-carbon sugar fermentation; d:to improve the efficiency for the six-carbon sugar and five-carbon sugar co-fermentation to produce fuel ethanol; e:to re-ferment the sweet sorghum waste after fermentation to further produce ethanol. It is the key factor to identify appropriate strains and fermentation processes in accordance to different varieties of sweet sorghum, to effectively increase the ethanol yield, to optimize the sweet sorghum straw resource utilization, and to reduce ethanol production cost for enhanced commercialization potential.