J Environ Qual. 2013 Sep;42(5):1441-8. doi: 10.2134/jeq2012.0499.
Extracellular polymeric substances (EPS) secreted by microorganisms make up an important constituent of labile and semilabile dissolved organic matter in surface water. There are no literature reports on the capability of EPS to reduce organic pollutants. This study demonstrated that EPS could effectively reduce a probe nitroaromatic compound, 1,3-dinitrobenzene. In aqueous dissolved EPS (60.3 mg L, produced by ), 1,3-dinitrobenzene (2.1 mg L) was completely reduced to 3-hydroxylaminonitrobenzene and 3-nitroaniline within 45 h (30°C; pH 5.6). The reduction of 1,3-dinitrobenzene followed pseudo-first-order kinetics (rate constant [], 4.3 × 10 h). Fourier transform infrared and C nuclear magnetic resonance spectroscopy analyses combined with Tollen's test suggest that hemiacetal of rhamnose structures and reduced phenolic groups in EPS acted as the reducing agents. The abiotic nature of the reaction was further verified by the electrochemical cell experiments where the measured quantity of electron transfer through the external circuit was in principle equal to the stoichiometric demand to reduce 1,3-dinitrobenzene. The reduction of 1,3-dinitrobenzene by EPS was markedly facilitated by the addition of model juglone (1 mg L), confirming the "electron shuttle" role of quinoid-like structures in EPS. Moreover, the reaction was dependent on the pH and the concentration of metal ions (Na, Zn, or Cu). Additional tests confirmed the universality of 1,3-dinitrobenzene reduction by other sources of EPS (, , , and natural freshwater biofilm). The results indicate that EPS are reductively labile and can contribute to the natural attenuation and remediation of environmental organic contaminants.
胞外聚合物（EPS）是微生物分泌的物质，构成了地表水不稳定和半不稳定溶解有机物质的重要组成部分。目前还没有文献报道 EPS 具有还原有机污染物的能力。本研究表明，EPS 可以有效地还原探针硝基芳烃化合物 1,3-二硝基苯。在水相溶解的 EPS（由 产生，浓度为 60.3 mg/L）中，1,3-二硝基苯（浓度为 2.1 mg/L）在 45 h（30°C；pH 值为 5.6）内完全被还原为 3-羟氨基硝基苯和 3-硝基苯胺。1,3-二硝基苯的还原遵循准一级动力学（速率常数 []，4.3×10 h）。傅里叶变换红外和 C 核磁共振光谱分析结合 Tollens 试验表明，EPS 中的鼠李糖半缩醛结构和还原的酚基团充当了还原剂。通过电化学池实验进一步验证了反应的非生物性质，通过外部电路传递的电子数量的测量值在原则上与还原 1,3-二硝基苯的化学计量需求相等。添加模型胡桃醌（1 mg/L）显著促进了 EPS 对 1,3-二硝基苯的还原，证实了 EPS 中类醌结构的“电子穿梭”作用。此外，该反应依赖于 pH 值和金属离子（Na、Zn 或 Cu）的浓度。进一步的测试证实了其他来源的 EPS（ 、 、 、和天然淡水生物膜）还原 1,3-二硝基苯的普遍性。结果表明，EPS 具有还原稳定性，可以促进环境有机污染物的自然衰减和修复。
