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Abstract：
Bacteria often respond to dynamic soil environment through the secretion of extracellular polymeric substances (EPS). The EPS modifies cell surface properties and soil pore-scale hydration status, which in turn, influences bacteria transport in soil. However, the effect of soil particle size and EPS-mediated surface properties on bacterial transport in the soil is not well understood. In this study, the simultaneous impacts of EPS and collector size on Escherichia coli (E. coli) transport and deposition in a sand column were investigated. E. coli transport experiments were carried out under steady-state flow in saturated columns packed with quartz sand with different size ranges, including 0.300-0.425 mm (sand-I), 0.212-0.300 mm (sand-II), 0.106-0.150 mm (sand-III) and 0.075-0.106 mm (sand-IV). Bacterial retention increased with decreasing sand collector size, suggesting that straining played an important role in fine-textured media. Both experiment and simulation results showed a clear drop in the retention rate of the bacterial population with the presence of additional EPS (200 mg L-1) (EPS+). The inhibited retention of cells in sand columns under EPS+ scenario was likely attributed to enhanced bacteria hydrophilicity and electrostatic repulsion between cells and sand particles as well as reduced straining. Calculations of the extended Derjaguin-Landau-Verwey-Overbeek (XDLVO) interactions energies revealed that high repulsive energy barrier existed between bacterial cells and sand particles in EPS+ environment, primarily due to high repulsive electrostatic force and Lewis acid-base force, as well as low attractive Lifshitz-van der Waals force, which retarded bacterial population deposition. Steric stabilization of EPS would also prevent the approaching of cells close to the quartz surface and thereby hinder cell attachment. This study was the first to show that EPS reduced bacterial straining in saturated porous media. These findings provide new insight into the functional effects of extrinsic EPS on bacterial transport behavior in the saturated soil environment, e.g., aquifers.
摘要：
细菌通常通过分泌胞外聚合物（EPS）来响应动态土壤环境。EPS改变了细胞表面性质和土壤孔隙尺度的水化状态，反过来，影响土壤中细菌的运输。然而,土壤粒径和EPS介导的表面特性对土壤中细菌迁移的影响尚不清楚。在这项研究中,EPS和收集器大小对大肠杆菌的同时影响(E.研究了大肠杆菌）在砂柱中的迁移和沉积。在不同粒径范围的石英砂填充的饱和柱中，在稳态流动下进行大肠杆菌转运实验。包括0.300-0.425mm(砂-I),0.212-0.300mm(砂型II),0.106-0.150毫米（砂-III）和0.075-0.106毫米（砂-IV）。细菌滞留量随着集沙器尺寸的减小而增加，这表明应变在精细纹理介质中起着重要作用。实验和模拟结果均显示，在存在额外的EPS（200mgL-1）（EPS）的情况下，细菌种群的保留率明显下降。在EPS情景下，细胞在沙柱中的抑制保留可能归因于增强的细菌亲水性和细胞与沙粒之间的静电排斥以及减少的应变。扩展的Derjaguin-Landau-Verwey-Overbeek（XDLVO）相互作用能量的计算表明，在EPS环境中，细菌细胞和沙粒之间存在高排斥能屏障，主要是由于高排斥力和路易斯酸碱力，以及低吸引力的利夫希茨-范德华力量，这阻碍了细菌种群的沉积。EPS的空间稳定还将防止细胞接近石英表面,从而阻碍细胞附着。这项研究首次表明EPS减少了饱和多孔介质中的细菌菌株。这些发现为外部EPS对饱和土壤环境中细菌运输行为的功能影响提供了新的见解。例如，含水层。
