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91.
Advances in the study of directed evolution for cellulases 总被引:1,自引:0,他引:1
Hailong LIN Weiguang LI Changhong GUO Sihang QU Nanqi REN 《Frontiers of Environmental Science & Engineering》2011,5(4):519-525
If cellulose can be effectively hydrolyzed into glucose by cellulase, the production costs of hydrogen, ethanol or other chemicals from cellulosic materials will be greatly decreased, and economically viable production of biohydrogen and bioethanol will become feasible. Cellulose is degraded into glucoses by multi-component enzyme systems. Nowadays cellulases are widely used in brewing, food, bioenergy, fodder, textiles, paper, pharmaceuticals, environmental protection and other industries. However, existing cellulases have several problems that limit their wider applications, including the low turnover number for solid cellulosic materials, and low stability in adapting to various application conditions. For example, high temperature, low pH, and so on. Application of directed evolution technology may be one of the most effective ways for improving the characteristics of cellulases. This paper presents a brief review of the cellulose hydrolysis mechanism by cellulase, advances in cellulases (endoglucanase and β -glucosidase) improvement by directed evolution for several characteristics (for instance, thermal stability, pH adaptability and enzyme activity), limitations of directed evolution for cellulases, and the outlook for directed evolution for cellulase. 相似文献
92.
对羧甲基纤维素(CMC)进行改性,并将其用于吸附废水中的铀.研究结果表明:在温度为70℃~80℃、单体质量浓度为30%~35%、羧甲基纤维素:丙烯酸(质量比)为10:2.5、反应时间为3.5~4h条件下,CMC改性效果最好;在改性CMC质量浓度为0.10g/L,温度为25℃, pH值为5.0,反应时间60min的条件下,对废水中铀去除率达到了97.1%;改性CMC对溶液中U(VI)的吸附过程符合Freundlich方程,其吸附动力学数据符合准一级方程(R2=0.9618),表明改性CMC的吸附主要是表面吸附;热力学研究表明,改性CMC对铀的吸附吉布斯自由能(ΔG0)0,吸附过程是自发的吸热反应、以物理吸附为主的过程. 相似文献
93.
94.
Many forms of industrial cellulose nitrate burn fiercely with the emission of large quantities of thermal radiation. Models are considered for predicting the variation with distance of the irradiance from burning cellulose nitrate. These models are evaluated using data from HSE and German trials. An approach to setting quantity safety distances for cellulose nitrate is given. 相似文献
95.
Ivars Pavasars Jessika Hagberg Hans Borén Bert Allard 《Journal of Polymers and the Environment》2003,11(2):39-47
Cellulose powder and softwood sawdust were subjected to alkaline degradation under conditions representative of a cementitious environment for periods of 7 and 3 years, respectively. During the first 3 years, sampling was frequent, and data on the degradation of cellulose and production of isosaccharinic acid was used for establishing long-term prediction models. Samples after an additional period of 4 years were compared to the predicted values. The total rate of degradation was measured as the increase in total organic carbon (TOC) in corresponding solutions. A previously published theoretical model of degradation kinetics gave a good approximation of the present experimental data. Peeling-off, stopping, and alkaline hydrolysis reaction rate constants were obtained as model parameters, and the results suggested that the transformation of the glucose end group is the rate-limiting step in the cellulose peeling-off reaction and also determines the pH dependence of that reaction. After 3 years, isosaccharinic (ISA) acid represented 70–85% of all degradation products as quantified by capillary zone electrophoresis. The long-term prediction model indicated that all of the cellulose would be degraded after only 150–550 years. The control sampling after 7 years points toward a lower degradation of cellulose and production of ISA than predicted by the model, reflecting either a degradation of ISA that was faster than the production or a termination of the ISA production. 相似文献
96.
97.
以玉米秸秆为底物的纤维素降解菌与产电菌联合产电的可行性 总被引:1,自引:0,他引:1
利用单室空气阴极微生物燃料电池(MFC)反应器,以玉米秸秆为底物,以本实验室筛选和保存的纤维素降解菌Chaetomium sp.和Bacillus sp.,以及纤维素降解混合菌PCS-S和H-C为秸秆降解的生物催化剂,探讨了以汽爆秸秆固体为底物进行微生物产电的可行性.结果表明,在MFC系统内,纤维素降解纯菌和混合菌均能使纤维素降解,但产生的电压很低(<90mV,1000Ω),升高温度(30~38.5℃)对电压输出无明显影响.单独以生活污水作为菌源不能直接降解秸秆产电.只有将H-C和生活污水(产电菌源)混合作为接种体,MFC才能获得较高的电压输出.此时得到的以汽爆秸秆固体作为底物时的最大功率密度为406mW·m-2,仅比葡萄糖作为底物时所得到的最大功率密度510 mW·m-2低20%. 相似文献
98.
针对黄麻生物脱胶废水浓度高、处理难度大的问题,采用水解酸化与膜生物反应器组合工艺对黄麻生物脱胶废水进行了处理试验。考察水解酸化池对COD、氨氮、木质素等的去除效果;并通过调节试验条件,考察水力停留时间、pH值、温度等因素对水解酸化效果的影响,得出处理黄麻生物脱胶废水的最佳实验条件。结果表明,水解酸化预处理工艺提高了废水的可生化性,对COD、氨氮均有较高的去处效率,对于降低纤维素的聚合度、促成纤维素的水解起到了关键的作用,为后续的好氧处理创造了有利条件。试验在水力停留时间10 h下,COD与氨氮去处率最高分别达35%,40%;影响水解酸化的因素主要为pH值和水力停留时间。 相似文献
99.
简要介绍了纤维素及其衍生物的分类及其特性,综述归纳了纤维素的缓蚀机理,系统概述了植物纤维素及其衍生物,纳米纤维素在缓蚀系统中的多种缓蚀作用,同时以植物纤维素和纳米纤维素的结构特性为依据,讨论了细菌纤维素在金属缓蚀系统中的应用前景。最后提出羧甲基纤维素与羟乙基纤维素及它们各自的衍生物应用范围广,但受温度影响较大。纤维素纳米晶体在金属防护方面有很好的应用前景,也是未来研究的重点。细菌纤维素有望成为一种高效、绿色的新型缓蚀剂,但目前还未引起研究人员足够的重视,对其制备方法和缓释机理还需要进行深入研究。 相似文献
100.
农作物秸秆结构复杂,酸化效果可能与传统糖类物料不一致。为方便考察纤维素类物料厌氧酸化效果,文章选取成分相对单一的滤纸为原料,考察了酶活浓度、反应时间、酵母菌接种量(F/M)等因素对纤维素经纤维素酶和酵母菌联合作用后的乙醇、乙酸产量的影响,及对厌氧发酵过程的影响分析。结果表明,当纤维素酶单独作用时,酶活浓度120 U/g、温度50℃、pH值4.8、水解24 h时可获得最大葡萄糖产率:73.7 mg/g(转化率为24.9%);纤维素酶和酵母菌分步糖化发酵(separate hydrolysis and fermentation,SHF)工艺中,F/M值为2:1、反应96 h可得最大乙醇产率:119.3 mg/g(转化率为42%);纤维素酶和酵母菌同步糖化发酵(simultaneous saccharification andfermentation,SSF)工艺中,F/M值为1:2、反应120 h得到最大乙醇产率:396.0 mg/g(转化率为58.2%)。F/M值为2:1、反应120 h时,SSF工艺比SHF工艺的乙醇产量提高了34.91%。 相似文献