LMEI, SOAS, University of London, UK.
Environ Sci Process Impacts. 2017 Apr 19;19(4):622-634. doi: 10.1039/c6em00666c.
In this research, bacterial cell attachments to hematite, goethite and aluminium hydroxide were investigated. The aim was to study the effects of these minerals' hydrophobicity and pH-dependent surface charge on the extent of biofilm formation using six genetically diverse bacterial strains: Rhodococcus spp. (RC92 & RC291), Pseudomonas spp. (Pse1 & Pse2) and Sphingomonas spp. (Sph1 & Sph2), which had been previously isolated from contaminated environments. The surfaces were prepared in a way that was compatible with the naturally occurring coating process in aquifers: deposition of colloidal particles from the aqueous phase. The biofilms were evaluated using a novel, in situ and non-invasive technique developed for this purpose. A manufactured polystyrene 12-well plate was used as the reference surface to be coated with synthesized minerals by deposition of their suspended particles through evaporation. Planktonic phase growth indicates that it is independent of the surface charge and hydrophobicity of the studied surfaces. The hydrophobic similarities failed to predict biofilm proliferation. Two of the three hydrophilic strains formed extensive biofilms on the minerals. The third one, Sph2, showed anomalies in contrast to the expected electrostatic attraction between the minerals and the cell surface. Further research showed how the solution's ionic strength affects Sph2 surface potential and shapes the extent of its biofilm formation; reducing the ionic strength from ≈200 mM to ≈20 mM led to a tenfold increase in the number of cells attached to hematite. This study provides a technique to evaluate biofilm formation on metal-oxide surfaces, under well-controlled conditions, using a simple yet reliable method. The findings also highlight that cell numbers in the planktonic phase do not necessarily show the extent of cell attachment, and thorough physicochemical characterization of bacterial strains, substrata and the aquifer medium is fundamental to successfully implementing any bioremediation projects.
本研究调查了细菌细胞对赤铁矿、针铁矿和氢氧化铝的附着。目的是研究这些矿物的疏水性和 pH 依赖性表面电荷对生物膜形成程度的影响，使用了六种遗传上不同的细菌菌株：从污染环境中分离出的 Rhodococcus spp.（RC92 和 RC291）、Pseudomonas spp.（Pse1 和 Pse2）和 Sphingomonas spp.（Sph1 和 Sph2）。表面的制备方式与含水层中自然发生的涂层过程相兼容：从水相沉积胶体颗粒。使用为此目的开发的新型原位和非侵入性技术评估生物膜。制造的聚苯乙烯 12 孔板用作参考表面，通过蒸发沉积悬浮颗粒来涂覆合成矿物。浮游相生长表明它独立于研究表面的表面电荷和疏水性。疏水性相似性未能预测生物膜增殖。三种亲水菌株中的两种在矿物上形成了广泛的生物膜。第三种，Sph2，表现出异常，与矿物和细胞表面之间预期的静电吸引相反。进一步的研究表明，溶液的离子强度如何影响 Sph2 表面电位并影响其生物膜形成的程度；将离子强度从约 200mM 降低至约 20mM 会导致附着在赤铁矿上的细胞数量增加十倍。这项研究提供了一种在受控条件下评估金属氧化物表面生物膜形成的技术，使用简单可靠的方法。研究结果还强调，浮游相中的细胞数量不一定显示细胞附着的程度，对细菌菌株、基质和含水层介质进行彻底的物理化学特性表征对于成功实施任何生物修复项目至关重要。
