Department of Chemical Engineering, McGill University, Montreal, Quebec, Canada H3A 2B2.
J Colloid Interface Sci. 2010 Apr 15;344(2):492-6. doi: 10.1016/j.jcis.2009.12.043. Epub 2009 Dec 28.
The microbial adhesion to hydrocarbons (MATH) assay has been used widely to characterize microbial cell hydrophobicity and/or the extent of cell adhesion to hydrophobic liquids. The classical MATH assay involves spectrophotometric absorbance measurements of the initial and final cell concentrations in an aqueous cell suspension that has been contacted with a hydrocarbon liquid. In this study, microscopic examination of the aqueous cell suspension after contact with hexadecane or a hexadecane/toluene mixture revealed the presence of hydrocarbon droplets. The hydrocarbon droplets contributed to the absorbance values during spectrophotometric measurements and caused erroneous estimates of cell concentrations and extents of microbial adhesion. A modified MATH assay that avoids such artefacts is proposed here. In this modified assay, microscopic examination of the aqueous suspension and direct cell counts provides cell concentrations that are free of interference from hydrocarbon droplets. The presence of hydrocarbon droplets was noted in MATH assays performed with three bacterial strains, and two different hydrocarbons, at ionic strengths of 0.2 mM and 20 mM and pH 6. In these experiments, the formation of quasi-stable hydrocarbon droplets cannot be attributed to the presence of biosurfactants, or stabilization by biocolloids. The presence of surface potential at the hydrocarbon-water interface that was characterized by electrophoretic mobility of up to -1 and -2 microm cm/Vs, likely caused the formation of the quasi-stable hydrocarbon droplets that provided erroneous results using the classical MATH assay.
微生物对烃类物质的粘附（MATH）测定法已广泛用于表征微生物细胞疏水性和/或细胞对疏水性液体的粘附程度。经典的 MATH 测定法涉及到在与烃类液体接触后的水相细胞悬浮液中初始和最终细胞浓度的分光光度吸光度测量。在这项研究中，接触十六烷或十六烷/甲苯混合物后的水相细胞悬浮液的显微镜检查显示存在烃类液滴。烃类液滴对分光光度测量中的吸光度值有贡献，并导致细胞浓度和微生物粘附程度的错误估计。这里提出了一种避免这种假象的改良 MATH 测定法。在这种改良的测定法中，通过显微镜检查水悬浮液和直接细胞计数，可以提供不受烃类液滴干扰的细胞浓度。在三种细菌菌株和两种不同烃类物质的 MATH 测定中都观察到了烃类液滴的存在，离子强度分别为 0.2 mM 和 20 mM，pH 值为 6。在这些实验中，准稳定烃类液滴的形成不能归因于生物表面活性剂的存在或生物胶体的稳定作用。在烃-水界面处存在表面电势，其特征是电泳迁移率高达-1 和-2 µm cm/Vs，可能导致形成准稳定的烃类液滴，使用经典的 MATH 测定法会得到错误的结果。
