【作者】 沈楠；

【导师】 曾建雄；

【作者基本信息】 中国科学技术大学 ， 环境工程， 2014， 博士

【摘要】 厌氧微生物体系利用有机质为底物进行代谢反应,有机质的氧化还原反应是该体系中生化反应的本质。目前学者在厌氧条件下利用微生物产生的还原力进行了一系列的研究,包括利用还原力还原降解某些污染物,产生新能源等。同时,在降解水体有机质方面也做了大量的研究,研究表明厌氧微生物体系具有强大的处理能力和经济价值,但对其作用机制缺乏深入的认识。因此,本课题通过系统的科学研究,探索其反应机理,发现其本质规律,呈献给研究人员一个整体结构。主要研究内容和研究结果如下：1.利用三氧化钨电致变色的特性进行高通量筛选产电菌株,在24孔板中进行产电微生物的筛选,能将电子导出体外的产电微生物可以使三氧化钨由白色变为蓝色。在环境样品巢湖底泥中筛选出27株产电微生物,大部分属于气单胞菌属和希瓦氏菌属。其中有一株乙酸氧化产电菌是兼性厌氧菌,对其产电性能和甲基橙还原脱色的性能进行了考察,证实了其胞外电子传递能力。这种类型的菌株在自然环境体系尤其是好氧和厌氧体系的交界处有很重要的作用,本研究在电化学活性细菌分布和代谢功能方面提供了一个全新视角。2.研究了Caldicellulosiruptor saccharolyticus体系中葡萄糖发酵产氢的过程,研究表明C. saccharolyticus葡萄糖发酵的主要产物和生成的先后顺序为氢气和乙酸首先出现,随后是乙醇和乳酸,在不同的葡萄糖浓度1.0g/L、2.0g/L、3.5g/L和7.5g/L下,最大的光密度值(OD620)分别为0.35、0.48、0.53、0.55,发现在不同的葡萄糖浓度下氢气／乙酸都大于2,介于2和4之间。为了探索造成这一现象的原因,通过外界添加同位素标记乙酸来追踪乙酸去向确定原因。实验表明60%的同位素标记乙酸转移到胞内转化为同位素标记乙醇,体系中没有产生明显的同位素标记二氧化碳,在对照组和放射性标记组同时检测到大约相同量的13CO2(O.lmmol),说明C. saccharolyticus体系中没有乙酸氧化现象发生。当生物质的增长值反算回乙酰辅酶A,与乙酸测定值相加得到理论乙酸产量,进行H2/acetate比值的修正之后,原本大于2的比值修正后都是接近2的,进一步证实了生物质增长是造成H2/acetate比值偏高的原因。3.首次研究报道了C. saccharolyticus在葡萄糖发酵过程中对甲基橙的降解,并提出了降解机理。C. saccharolyticus在自身所产的溶解氢的作用下,可将甲基橙降解为DPD和4-ABA, C. saccharolyticus细胞在这个过程中起至关重要的作用,因为甲基橙和氢气的化学反应是极其微弱有限的,但是在细胞表面酶Ni-Fe氢化酶的催化作用下两者可以快速反应,从而完成甲基橙脱色。甲基橙降解速率和溶解氢的浓度呈正相关性,在高溶解氢条件下脱色速率可达6.65mg/L/h或7.08mg/L/h,相反,在刚刚进行氮气吹扫后的低溶解氢条件下却只有2.16mg/L/h或0.88mg/L/h。提出的脱色机理能很好的解释添加甲基橙后还原产物乙醇产量的变化现象,这很可能是甲基橙对还原力的竞争造成的,使得葡萄糖发酵产物中还原产物产量降低。4.在强高温产氢菌株C. saccharolyticus体系中,葡萄糖发酵过程中原位产生的氢气可以将Pd(Ⅱ)还原为Pd(0),采用透射电子显微镜结合X射线探测器的检测方法证实了这一科学猜测。零价钯颗粒被用于甲基橙脱色和泛影酸钠脱碘的催化反应中,100mg/L的甲基橙在有钯添加的实验组中半小时内即被降解完毕,而没有钯添加的实验组中完全降解则需要6小时之久。20mg/L的泛影酸钠在有钯添加的实验组中10分钟即被降解完毕,没有钯添加的实验组几乎没有降解,说明零价钯强化了降解效果。甲基橙的脱色是在氢气、氢化酶和零价钯颗粒共同作用下完成的,而泛影酸钠的降解过程中氢化酶并没有起到明显作用,零价钯颗粒是脱碘过程中起本质作用的催化剂。更重要的是C. saccharolyticus菌体起到分散剂的作用,使形成的零价钯颗粒分散均匀,颗粒成纳米级,是一种绿色的分散体系,而且在此体系中形成的纳米钯颗粒相较于没有分散剂形成的零价钯颗粒具有更好地催化效果。总而言之,钯的参与是强化水体污染物的降解效果的很好的选择。更多还原

【Abstract】 Organic matter is applied by anaerobic microbe as substrate for all the metabolic reactions in vivo. The REDOX reaction of organic matter is the essence of biochemical reactions in the anaerobic system. At present, many researchers have carried out a series of studies of the reducing power produced by anaerobe. The reductive degradation of some pollutants, the production of new electrical energy and the degradation of organic matter in water were included. Those studies have shown that the system of anaerobic microbial had a strong processing power and economic value. However, the mechanism in the system was not explained clearly. Therefore, this study attempted to explore the reaction mechanism and found the nature of law through scientific research systematically. The main research contents and research results are as follows:1.27strains of electrochemically active bacteria (EAB) were rapidly isolated and their capabilities of extracellular electron transfer were identified using a photometric method based on WO3nanoclusters. These strains caused color change of WO3from white to blue in a24-well agar plate within40h. Most of the isolated EAB strains belonged to the genera of Aeromonas and Shewanella. One isolate, Pantoea agglomerans S5-44, was identified as an EAB that can utilize acetate as the carbon source to produce electricity and reduce azo dyes under anaerobic conditions. The results confirmed the capability of P. agglomerans S5-44for extracellular electron transfer. The isolation of this acetate-utilizing, facultative EB A reveals the metabolic diversity of environmental bacteria. Such strains have great potential for environmental applications, especially at interfaces of aerobic and anaerobic environments, where acetate is the main available carbon source.2. The ratio of H2/acetate in glucose fermentation shall be equal or less than2. However, the ratio over2is found in the literature. Two possible reasons were proposed in this study:acetate oxidation or biomass growth via acetyl-CoA. In order to find out the right reason, glucose fermentation by Caldicellulosiruptor saccharolyticus was investigated. Under different glucose concentrations (1.0g/L,2.0g/L,3.5g/L and7.5g/L), the Optical Density (OD620) reached a maximum value of0.35,0.48,0.53and0.55, respectively. It was found that the ratios of H2/acetate under different glucose concentrations were all greater than2. When CH3-13COOH was added to the system,60%of CH3-13COOH was converted to isotope ethanol. About the same amount of13CO2(0.01mmol) was detected in both the control and isotopie experiments, illustrating acetate oxidation didn’t occur in this study. The corrected ratio of H2/acetate after the compensation from biomass growth was around2, demonstrating the biomass growth from acetyl-CoA was the right reason for the abnormal high ratio.3. It is worth to study the decolorization ability of C. saccharolyticus under the optimum growth temperature of70℃in thermal spring, for example. For the first time, this study demonstrated that C. saccharolyticus could effectively degrade methyl orange (MO) to4-aminobenzenesulfonic acid (4-ABA) and N’,N-dimethyl-p-phenylenediamine (DPD) with dissolved hydrogen (DH) as the reducing equivalent. The decolorization reaction was catalyzed by Ni-Fe hydrogenase. The reaction rate was positively related to the DH concentrations. For example, the decolorization rates were6.65and7.08mg/L/h at higher DH, but decreased to2.16and0.88mg/L/h after N2purging. Furthermore, the addition of MO in glucose fermentation decreased the ethanol yield due to the limited reducing equivalents. It could be conjectured that the competition for hydrogen between azo dyes reduction and hydrogenotrophic methanogenesis processes might also exist in mixed culture fermentation.4. This study focused on examining the general applicability of coupling bio-Pd nanoparticle generation and bio-H2produced by C. saccharolyticus for water treatment under extreme-thermophilic conditions. Palladium was added to cell cultures to achieve a final Pd concentration of50mg L-1. Methyl orange and diatrizoate were chosen as the contaminants in water. MO (100mg/L) was degraded within30min in the cultures with Pd added, while6hours were needed without Pd addition. Diatrizoate (20mg/L) was degraded within10min in Pd added cultures. However, diatrizoate was not degraded in the culture without Pd. The degradation rates were positively correlated with dissolved hydrogen generated by C. saccharolyticus. Furthermore, the catalytic actions of Pd(0) nanoparticle and cell were distinguished during the degradation process. And cells of C. saccharolyticus dispersed the Pd(0) particles well and showed a better catalytic activity than chemic-Pd(O) without dispersant. Dissolved hydrogen produced by C. saccharolyticus should be the perfect reduction equivalent for Pd formation. Generally speaking, the biodegradation proceeding with the action of in situ bio-H2in natural environment of high temperature should be illuminated.更多还原