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木质纤维素水解酸化菌系的筛选及应用
Alternative TitleScreening and Application of the Microbial Community with the Ability of Lignocellulose Hydrolysis and Acidification
张翔
Subtype博士
Thesis Advisor陈洪章
2012-12-01
Degree Grantor中国科学院研究生院
Degree Discipline生物化工
Keyword汽爆秸秆   混合菌系   水解酸化
Abstract木质纤维素资源蕴含丰富,其往往经过酶解转化为糖类物质,然后以此为平台底物通过微生物转化,用于生产生物能源、化学试剂、化工产品等高附加值产品。然而在木质纤维素酶解过程中仍然存在纤维素酶成本较高,纤维素酶、半纤维素酶等比例不适,酶解过程中易造成无效吸附等问题,降低了木质纤维素的利用率。本文从筛选木质纤维素水解酸化菌系入手,对该菌系水解酸化木质纤维素的情况进行了较为系统的研究,并考察了该酸化液作为碳源进行二次发酵的可行性,以期探索木质纤维素资源利用的新途径。论文所取得的主要成果如下:(1) 从富含纤维素降解菌的环境中筛选到一组木质纤维素水解酸化菌系。以汽爆玉米秸秆为发酵底物,从鸡粪、牛粪和取自污水处理厂的厌氧活性污泥等富含纤维素降解菌的环境中,通过连续传代的方法,获得一组具有高效水解酸化木质纤维素能力的复合菌系。该菌系在50 °C下静置培养,经7 d发酵,可降解91%的滤纸,62%的汽爆秸秆,乙酸和丙酸为主要的中间代谢产物,经PCR-DGGE分析发现,在发酵过程中菌系中的优势菌群主要为Bacillus属和Clostridium属。(2) 通过间歇调节pH的方式,研究了pH对该菌系水解酸化汽爆秸秆的影响。研究发现,当pH调节为pH9.0时,具有强化汽爆秸秆水解酸化的作用,汽爆秸秆降解率达到75%,而乙酸、丙酸二者浓度的峰值达到3.32 g/L。经PCR-DGGE分析,pH的改变导致菌系中优势菌群发生变化,这可能是进一步导致发酵模式发生改变的原因之一。(3) 研究了几种常用的木质纤维素预处理方法(稀酸预处理、碱预处理、汽爆预处理、微波预处理等),对该菌系水解酸化木质纤维素的影响。研究发现,经不同方式预处理后,玉米秸秆纤维素、半纤维素等组分发生相应地变化。其中,经汽爆预处理和碱预处理的玉米秸秆水解酸化效果较好,降解率分别达到64%和59%,乙酸、丙酸二者浓度的峰值分别达到2.14g/L和2.52g/L。(4) 探索了污泥热碱预处理液与汽爆秸秆共发酵的可行性。研究发现,当添加污泥热碱处理液体积为10 mL时,汽爆秸秆降解率最大,达到68%,乙酸为主要发酵产物,其浓度峰值达到2.53g/L。(5) 探索了汽爆秸秆水解酸化液作为碳源进行二次发酵的可行性。研究发现,汽爆秸秆酸化液通过减压蒸馏浓缩分离,其主要成分为乙酸、丙酸、乙醇和丁酸,以R. eutropha H16作为发酵菌株,在48h摇瓶实验中,细胞干重达到3.5 g/L。
Other AbstractLignocellulosic feedstock is an abundant resource. It is usually enzymatic hydrolyzed to sugars as intermediate feedstock chemicals, which are converted further to biofuels, chemical reagents and chemical products with high value-added by microbial transformation. However, during the enzymatic process of lignocellulose, it still exists some problems, such as high cost of cellulase, incompatible cellulase and hemicellulase proportion, invalid adsoption of cellulase, and etc. Therefore, it reduces the resource utilization of the lignocellulose.In this paper, starting from the screening of microbial community with the ability of lignocellulose hydrolysis and acidification, we examined the hydrolysis and acidification of lignocelluloses with the enriched microbial community. We also examined the feasibility of fermentation products during hydrolysis and acidification process as carbon source for the secondary fermentation. The aim of the paper was to explore new ways of lignocellulose utilization. The main results of the paper were as follows:(1) We obtained a microbial community capable of hydrolysis and acidification of SEC enriched by successive subcultivation. Chicken feces, cattle feces, and anaerobic sludge collected from a wastewater treatment plant were used as origins for enrichment of microbial community. The obtained microbial community could degrade 91% of filter paper and 62% of SEC after 7 d cultivation at 50 °C. Acetate and propionate were the major intermediate metabolites treating SEC as substrates. Based on the analysis of PCR-DGGE, it was found that Bacillus and Clostridium were dominant microbial populations. (2) Intermittent pH adjustment was used to study the effect of pH on the hydrolysis and acidification of SEC. The results showed that pH 9.0 could enhance the degradation and acidification of SEC. The degradation rate of SEC was 75% and the total concentrations of major water soluble metabolites (acetate and propionate) were 3.32 g/L. Based on analysis of PCR-DGGE, different strains were dominant due to pH shift by intermittent adjustment, which might be one of the reasons for the change of fermentation patterns. (3) The effects of different pretreatments of cornstalks (acid pretreatment, alkali pretreatment, steam explosion pretreatment, microwave pretreatment) on the hydrolysis and acidification were studied. The results showed that there were compositional changes of SEC under different pretreatments. Steam explosion and alkali pretreatment were more favorable for the degradation of SEC and organic acid productions. The degradation rate of cornstalks pretreated by steam explosion and alkali were 64% and 59%, relatively. The peak values of total amounts of acetate and propionate were 2.14g/L and 2.52g/L, relatively.(4) The feasibility of co-fermentation of sewage sludge and SEC was examined. The results showed that the maximum degradation rate of SEC was 68%, adding 10 mL sewage sludge thermal-alkali treated solution. Acetate was the major water soluble metabolite. The peak value of acetate concentration was 2.53g/L. (5) The feasibility of organic acids produced by hydrolysis and acidification of SEC served as carbon source was investigated. The results showed that acetic acid, propionic acid, ethanol and butyric acid were the main products after vacuum distillation. And R. eutropha H16 produced 3.5 g/L cell dry weight, using concentrated solution as carbon source in a 48h shake flask growth.
Pages119
Language中文
Document Type学位论文
Identifierhttp://ir.ipe.ac.cn/handle/122111/8303
Collection研究所(批量导入)
Recommended Citation
GB/T 7714
张翔. 木质纤维素水解酸化菌系的筛选及应用[D]. 中国科学院研究生院,2012.
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