Abstract：
The transport and retention of bacteria in porous media, such as aquifer, are governed by the solid-liquid interface characteristics and bacterial mobility. The secretion of extracellular polymeric substance (EPS) by bacteria modifies their surface property, and thereby has effects on their adhesion to surface. The role of EPS in bacterial mobility within saturated quartz sand media is uncertain, as both promoting and inhibitory effects have been reported, and underlying mechanisms remain unclear. In this study, the effects of EPS on bacterial transport behavior and possible underlying mechanism were investigated at 4 concentrations (0 mg L-1, 50 mg L-1, 200 mg L-1 and 1000 mg L-1) using laboratory simulation experiments in conjunction with Extend Derjaguin-Landau-Verweu-Overbeek (XDLVO) modeling. The results showed that EPS facilitated bacterial mobility at all tested concentrations. It could be partially explained by the increased energy barrier between bacterial cells and quartz sand surface in the presence of EPS. The XDLVO sphere-plate model predicted that EPS induced a higher electrostatic double layer (EDL) repulsive force, Lewis acid-base (AB) and steric stabilization (ST), as well as a lower Lifshitz-van der Waals (LW) attractive force. However, at the highest EPS concentration (1000 mg L-1), the promotion of EPS on bacterial mobility weakened as a result of lower repulsive interactions between cells, which was supported by observed enhanced bacterial aggregation. Consequently, the increased aggregation led to greater bio-colloidal straining and ripening in the sand column, weakening the positive impact of EPS on bacterial transport. These findings suggested that EPS exhibited concentration-dependent effects on bacterial surface properties and transport behavior and revealed non-intuitive dual effects of EPS on those processes.
摘要：
细菌在多孔介质中的运输和滞留，比如含水层，受固-液界面特性和细菌流动性的控制。细菌分泌的胞外聚合物（EPS）改变了它们的表面性质，从而影响它们对表面的粘附。EPS在饱和石英砂介质中细菌迁移中的作用尚不确定，正如已经报道的促进和抑制作用，和潜在的机制仍不清楚。在这项研究中,采用实验室模拟实验结合ExtendDerjaguin-Landau-Verweu-Overbeek(XDLVO)模型,研究了4种浓度(0mgL-1,50mgL-1,200mgL-1和1000mgL-1)下EPS对细菌转运行为的影响及可能的潜在机制.结果显示,在所有测试浓度下,EPS促进细菌迀移。在EPS存在下，细菌细胞和石英砂表面之间的能量屏障增加可以部分解释。XDLVO球板模型预测EPS会引起更高的静电双层（EDL）排斥力，路易斯酸碱（AB）和空间稳定（ST），以及较低的Lifshitz-vanderWaals(LW)吸引力。然而,在最高EPS浓度（1000mgL-1）下，由于细胞之间的排斥相互作用较低，EPS对细菌移动性的促进作用减弱，这得到了观察到的增强的细菌聚集的支持。因此,增加的聚集导致沙柱中更大的生物胶体应变和成熟，削弱EPS对细菌转运的正向影响。这些发现表明，EPS对细菌表面特性和运输行为表现出浓度依赖性影响，并揭示了EPS对这些过程的非直观双重影响。
