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腐殖质是动植物或微生物残体经过生物、非生物的氧化、降解及聚合等多种作用形成的一种天然有机化合物,广泛存在于土壤、沉积物及河流、湖泊等水生环境中。土壤中腐殖质含量约占总有机质含量的 85%—90%,是有机质的主要组成部分[1]。腐殖质呼吸是近年来新发现的可参与环境污染生物降解的微生物能量代谢方式。腐殖质本身矿化率低,不易被微生物分解,但可作为微生物呼吸的电子受体参与有机物矿化过程,氧化小分子易降解有机质,产生 CO2,从而影响自然界的碳循环。在厌氧条件下,某些土壤与水体沉积物中,80%以上的有机碳矿化由微生物的腐殖质呼吸直接完成,超过产甲烷呼吸、硝酸盐呼吸、硫酸盐呼吸等其它代谢方式的总和[2]。同时腐殖质可作为氧化还原介体促进其他难降解污染物的生物还原,如偶氮染料[3-4],Fe(Ⅲ)和Cr(Ⅵ)[5],以及硝酸盐[6]等。可进行腐殖质呼吸的微生物被称为腐殖质还原菌[7],腐殖质还原菌以环境中有机底物为电子供体,以腐殖质及其醌类模式物为唯一电子受体进行电子传递。最早Lovley发现Geobacter metallireducens和Shewanellaalga可以利用蒽醌-2,6-双磺酸(AQDS)为电子受体加速有机质和H2的厌氧氧化[8]。腐殖质还原菌与腐殖质之间的电子穿梭对于有机污染物的降解转化具有重要意义。
腐殖质上的醌类结构是其作为氧化还原介体的活性组分[9],目前学者们以醌类物为腐殖质模式物已在土壤、河湖沉积物、堆肥以及水体等环境介质中富集分离出多种腐殖质还原菌[10—14],按照对氧气需求不同分为严格厌氧菌和兼性厌氧菌,主要以Proteobacteria、Acidobacteria与Firmicutes这3个门为主[9]。在腐殖质还原菌生物还原体系中,腐殖质还原菌的浓度和活性是醌类物发挥氧化还原介体作用催化生物反应的关键因素[15]。然而目前对腐殖质还原菌的生长特性及醌还原特性研究较少。
因此,本研究的主要对已经鉴定完的腐殖质还原菌Citrobacter freundii从碳源比、碳源浓度、C/N等角度优化其生长条件;了解腐殖质还原菌的生长与醌还原特性,并通过红外测定沉积物的结构,为其应用到河道沉积物修复领域提供理论依据;将腐殖质还原菌应用到河道沉积物修复领域,考察其降解沉积物有机质的能力,拓展修复河道沉积物的方法。
腐殖质还原菌特性及其在河道修复中的应用
Characteristics of humus reducing bacteria and their application in river remediation
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摘要: 腐殖质呼吸是近年来新发现的可参与环境污染生物降解的微生物能量代谢方式,腐殖质可作为氧化还原介体促进其他难降解污染物的生物还原,对有机污染物的降解转化具有重要意义。本研究采用响应曲面法优化菌株Citrobacter freundii的生长条件,并探究厌氧条件下Citrobacter freundii的醌还原广谱性;通过红外测定4种沉积物的官能团结构,探究Citrobacter freundii应用于河道沉积物修复领域的可行性。结果显示,当碳源比(葡萄糖/葡萄糖+柠檬酸钠)为0.691,碳源浓度为3.24 g·L−1,C/N(碳氮比)为15.096时,Citrobacter freundii的OD600与α-AQS还原率的最大预测值分别为0.481及36.84%;Citrobacter freundii对萘醌和蒽醌类的醌类物均具有还原活性;所选4种河道沉积物均含有C=O官能团,与醌类物结构相似;优化后的Citrobacter freundii削减沉积物有机质速度远高于未优化的削减速度,42 d有机质削减率为14.61%。本研究验证了Citrobacter freundii醌还原特性,拓展了腐殖酸还原菌的应用领域,为沉积物修复提供了新手段。Abstract: Humus respiration is a newly discovered microbial energy metabolism that can participate in the biodegradation of environmental pollution in recent years. Humus can be used as a redox mediator to promote the biological reduction of other refractory pollutants, which is of great significance for the degradation and transformation of organic pollutants. In this study, response surface methodology was used to optimize the growth conditions of Citrobacter freundii, and to explore the quinone reduction broad-spectrum of Citrobacter freundii under anaerobic conditions. The functional group structure of four kinds of sediments was measured by infrared to explore the feasibility of Citrobacter Freundii application in the field of river channel sediment remediation. The results showed that when the carbon source ratio (glucose/(glucose + sodium citrate)) was 0.691, the carbon source concentration was 3.24 g·L−1, and the C/N ratio was 15.096, the maximum predictive values of OD600 and α-AQS reduction rate of Citrobacter freundii were 0.481 and 36.84%, Citrobacter freundii has reductive activity on both naphthoquinone and anthraquinone quinones. The four selected river sediments contain C=O functional groups, which are similar to quinones in structure. The optimized Citrobacter freundii reduced the organic matter in sediments at a much higher rate than the unoptimized Citrobacter freundii, with a 42 d reduction rate of 14.61%. This study verified the reducing properties of Citrobacter freundii quinone, expanded the application field of humic acid reducing bacteria, and provided a new means for sediment remediation.
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Key words:
- humus respiration /
- quinone reduction /
- response surface /
- river remediation
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表 1 响应曲面实验因素水平表
Table 1. Response surface experimental factor level table
因素水平 A B/(g·L−1)当量葡萄糖 C/N -1 0 2.5 15 0 0.5 3.0 20 1 1 3.5 25 表 2 响应曲面实验设计方案与结果
Table 2. Response surface experimental design scheme and results
试验号 Experiment number 因素水平 Factor level 测定指标 Measurement index A B C Y1 Y2/% 1 1 1 0 0.160 33.7 2 0 0 0 0.335 37.8 3 0 0 0 0.411 37.4 4 0 1 −1 0.474 33.8 5 1 −1 0 0.154 25.5 6 0 0 0 0.341 35.1 7 −1 −1 0 0.066 6.76 8 0 1 1 0.419 36.9 9 0 −1 −1 0.332 17.5 10 −1 1 0 0.103 7.74 11 0 0 0 0.395 39.4 12 0 −1 1 0.341 18.0 13 0 0 0 0.375 45.1 14 1 0 −1 0.402 33.4 15 −1 0 1 0.117 8.18 16 1 0 1 0.109 40.4 17 −1 0 −1 0.074 6.41 表 3 OD600回归方程方差分析
Table 3. OD600 regression equation variance analysis
来源
Source平方和
Sum of squares自由度
Freedom均方
Mean squareF值
FP值
P显著性
Significance模型 0.31 9 0.035 13.97 0.0011 ** A 0.027 1 0.027 10.92 0.0131 * B 0.008646 1 0.008646 3.49 0.1039 C 0.011 1 0.011 4.42 0.0735 AB 0.0002403 1 0.0002403 0.097 0.7645 AC 0.028 1 0.028 11.4 0.0118 * BC 0.001024 1 0.001024 0.41 0.5407 A2 0.23 1 0.23 92.57 < 0.0001 ** B2 0.001264 1 0.001264 0.51 0.4981 C2 0.005897 1 0.005897 2.38 0.1667 残差 0.017 7 0.002476 失拟项 0.013 3 0.004315 3.93 0.1094 纯误差 0.004387 4 0.001097 总离差 0.33 16 注: **为差异高度显著(p<0.01);*为差异显著(p<0.05),下同.
Note: ** is highly significant difference (P < 0.01); * is highly significant difference (P < 0.05),the same below.表 4 α-AQS还原率回归方程方差分析
Table 4. Analysis of variance of regression equation for reduction rate of α-AQS
来源
Source平方和
Sum of squares自由度
Freedom均方
Mean squareF值
FP值
P显著性
Significance模型 2746.5548 9 305.1728 12.5016 0.0015 ** A 1349.6157 1 1349.6157 55.2881 0.0001 ** B 246.4932 1 246.4932 10.0978 0.0155 * C 19.1482 1 19.1482 0.7844 0.4052 AB 13.1916 1 13.1916 0.5404 0.4862 AC 6.8343 1 6.8343 0.2800 0.6131 BC 1.7438 1 1.7438 0.0714 0.7970 A2 659.6553 1 659.6553 27.0233 0.0013 ** B2 272.9482 1 272.9482 11.1815 0.0124 * C2 81.0666 1 81.0666 3.3210 0.1112 残差 170.8743 7 24.4106 失拟项 113.6563 3 37.8854 2.6485 0.1851 纯误差 57.2180 4 14.3045 总离差 2917.4291 16 表 5 Citrobacter freundii对不同醌类物的还原性能
Table 5. Reduction properties of Citrobacter freundii for different quinones
醌类物
Quinones醌还原率/%
Reduction rate of quinones12 h 24 h 48 h 72 h 96 h 指甲花醌 2.05 ± 0.15 4.55 ± 0.13 13.64 ± 0.54 18.18 ± 0.74 16.82 ± 0.13 AQS 2.56 ± 0.03 2.88 ± 0.48 27.93 ± 0.36 31.84 ± 0.43 24.16 ± 0.52 α-AQS 2.51 ± 0.47 5.73 ± 0.4 37.18 ± 0.86 60.17 ± 0.37 52.85 ± 1.11 -
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