| As the substitution of renewable fossil energy, biomass energy is getting more and moreattention around the world. Sweet sorghum is one of the important energy crops, which ishigh yield, drought and barren resistance. It not only provides sugar, but also provides a lot oflignocellulose materials to produce the cellulosic ethanol. Therefore, sweet sorghum is alsoregarded as one of the most promising energy crop. However, there are some questions aboutof the production of sweet sorghum bioethanol, for exemple, the complexity of preprocessorof lignocellulose, the low conversion efficiency of cellulose, the high cost of sugarconcentration, the low sugar utilization rate of stem juice during fermentation cycle. Thisresearch mainly has carried on the experimental research, aiming at the above limitingfactors.Sweet sorghum variety M81as the experimental material, the sweet sorghum bagasse(SSB) was treated under four conditions (lime at room temperature, lime with microwaveconditions, lime with autoclave conditions and sodium hydroxide at room temperature) withthe washed but untreated SSB as control. The changes of lignocellulose structure and thecellulase saccharifying efficiency of the materials under different conditions wereinvestigated. The results showed that the four treatments can effectively change thelignocellulose component of sweet sorghum bagasse, especially pretreated by NaOH underroom temperature for two weeks, and lime played an important role in hemicellulosedissolution too; Scanning electron microscopy (SEM) observated that the lignocellulosestructure were different after treatments of lime with autoclave treatment and NaOH at roomtemperature. The lignin structure after the lime with autoclave treatment eroded seriously andfragmentized adhere to the surface of cellulose, but the internal fiber structure still arrangedtightly; the latter deals with lignocellulose beam structure swelled degradation, and thecellulose fiber net appeared due to the surface component of lignin removed a lot was brokenand many small holes appeared. After the four pretreated methods, the cellulose andhemicellulose of sweet sorghum bagasse were enzymatic saccharified, the production concentration of glucose and xylose increased to control the1.5times,2.1times,1.9times,4.2times and3.1times,5.0times,4.9times and2.4times, respectively.In addition to, conducted the simultaneous saccharification fermentation tests for sweetsorghum stem juice and lignocellulose slag that they were mixed. Ethanol production rate areinfluenced by many conditions, and these what are as investigation content, inculding theratio of juice/slag, temperature, initial pH, the amount of cellulase, the inoculation quantity ofyeast. And the fermentation conditions are optimized by Box-Behnken; The results showedthat the optimal fermentation conditions of simultaneous saccharification mixed fermentationtests are ratio of juice/slag:5.93%(w/v);36.92℃; addition amount of cellulose enzyme:24.21FPU(NS50013),36.32CBU(NS50010)/g(SSB); inoculation quantity of yeast:8.38%(v/v). Under these conditions, the productive rate of ethanol achieve the highest, that is84.03%.In this study, genetic engineering is applied to reform the sugar metabolic genes of thestrains of Saccharomyces cerevisiae T1308, that enhanced glucose metabolism of yeast, andimproved fermentation efficiency. Extracting yeast DNA as template, designing primers, PCRresult get six strong constitutive promoter: TPI1p, HXT7p(486bp), PGK1p(646bp),FBA1p(642bp), ADH1p(1186bp), TDH3p(711bp) and six genes: xylulose kinaseXKS1(2177bp), transaldolase TAL1(1225bp), transketolase TKL1(2456bp), phosphoric acidketone sugar epimerase RPE1(882bp), ribose-5-phosphate isomerase RKI1(1019bp).Inaddition to, we also got three xylose isomerase XI from japonica ricethat, O type bacteria and301clostridium phytofermentans that are optimized. The promoters are fused with theircorresponding genes by fusion PCR, transformed these recombinants into saccharomycescerevisiae genome by LiAc chemical catalysisv and got three transgenetic yeast strains thatare able to metabolism the xylose and enhanced the sugar metabolism flow. The fermentationexperiment result showed that the xylose utilization rate of three transgenetic yeast strains are23.5%,24.9%,28.8%, respectively. The xylose utilization rate is3.21,3.41,3.94times ashigh as the control, respectively. Compared with original strain, the sugar metabolic rate areincreased, provided three transgenetic yeast strains for fuel ethanol production. |
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