Stimulatory Effect Of Biosurfactant On Rice Straw Degradation And New Fermentation Technology

As energy crisis coming, more and more researchers focus on the fermentation of cellulose to ehanol. Because of the complex configurations of cellulose and the low recycling of cellulase, the hydrolysis of cellulose to reducing sugars becomes the rate limiting step in the ethanol production process. In order to make the production of reducing sugars to the highest extent, this rate limiting step was studied in this article. As for the special agricultural structure in Shanghai City, rice straw was selected as degradation objective. Reducing sugars was produced by rice straw decomposing microorganisms, which could provide premise for ethanol production.Screened by cellulose-congo red plate and value of cellulases, an effective rice straw decomposing fungus named ZM-4, identified as Trichoderma reesei, was isolated from vegetable gardens, soil around rotten trees roots and deadwood. Through UV/DES compound alternative mutagenesis, an effective rice traw decomposing fungi named ZM4-F3 was screened form the original fungi ZM-4. Compared with ZM-4, the production of cellulases and reducing sugars, and the decomposing rate of rice straw and cellulose all increased when using Trichoderma reesei ZM4-F3 for rice straw decomposing. Cultivated for six continuous generations, ZM4-F3 could still keep a high stable capacity for rice straw decomposing, which can be served in industrial production.Rice straw was first pretreated by alkali, and the optimum conditions of pretreatment were discussed. Detected by SEM, significant morphological changes were observed in the tissue of rice straw. Through orthogonal experiments, the optimal conditions for hydrolysis of rice straw by Trichoderma reesei ZM4-F3 were observed. Moreover, the compositions of reducing sugars in enzymatic hydrolysates of rice straw were observed by GC analysis.As the stimulatory effect of surfactant on cellulose hydrolysis, an effective biosurfactant producing bacterium named BSZ-07 was obtained from oil-polluted soils through Blue Agar Plate screening and surface tension screening, which was identified as Pseudomonas aeruginosa. Based on orthogonal experiments, the optimal biosurfactant producing conditions by BSZ-07 was obtained. We discovered that high oil-water emulsion stability was held by BSZ-07, which showed it is a well biosurfactant producing bacterium. Analyzed by FITR, NMR and element composition, the biosurfactant produced by BSZ-07 was identified as rhamnolipid.Rhamnolipid was added to rice straw decomposing process to enhance the production of reducing sugars. On-site production of rhamnolipid was realized. Since the on-site production adding method could leave out the complex purification process, it could reduce the production cost of rhamnolipid effectively. This on-site production adding method was realized by two-stage co-hydrolysis by Trichoderma reesei ZM4-F3 and Pseudomonas aeruginosa BSZ-07. The optimum conditions of this two-stage co-hydrolysis bioprocess were observed, which showed that this new bioprocess not only could increase the production of reducing sugars and decomposing rate of rice straw, but also could reduce the hydrolysis time.At last, mechanisms of the stimulatory effects by rhamnolipid on rice straw hydrolysis were observed. The results showed that the increased activity ofβ-glucosidase, the increased stability of Cel7A, the increased Zeta potential of cellulose and the adsorption of rhamnolipid biosurfactant to lignin might be the important mechanisms responsible for the stimulatory effects by adding rhamnolipid.