Dorobantu Loredana S, Bhattacharjee Subir, Foght Julia M, Gray Murray R
Department of Chemical and Materials Engineering, University of Alberta, Edmonton, Alberta T6G 2G6, Canada.
Langmuir. 2008 May 6;24(9):4944-51. doi: 10.1021/la7035295. Epub 2008 Mar 21.
The structure and physicochemical properties of microbial surfaces at the molecular level determine their adhesion to surfaces and interfaces. Here, we report the use of atomic force microscopy (AFM) to explore the morphology of soft, living cells in aqueous buffer, to map bacterial surface heterogeneities, and to directly correlate the results in the AFM force-distance curves to the macroscopic properties of the microbial surfaces. The surfaces of two bacterial species, Acinetobacter venetianus RAG-1 and Rhodococcus erythropolis 20S-E1-c, showing different macroscopic surface hydrophobicity were probed with chemically functionalized AFM tips, terminating in hydrophobic and hydrophilic groups. All force measurements were obtained in contact mode and made on a location of the bacterium selected from the alternating current mode image. AFM imaging revealed morphological details of the microbial-surface ultrastructures with about 20 nm resolution. The heterogeneous surface morphology was directly correlated with differences in adhesion forces as revealed by retraction force curves and also with the presence of external structures, either pili or capsules, as confirmed by transmission electron microscopy. The AFM force curves for both bacterial species showed differences in the interactions of extracellular structures with hydrophilic and hydrophobic tips. A. venetianus RAG-1 showed an irregular pattern with multiple adhesion peaks suggesting the presence of biopolymers with different lengths on its surface. R. erythropolis 20S-E1-c exhibited long-range attraction forces and single rupture events suggesting a more hydrophobic and smoother surface. The adhesion force measurements indicated a patchy surface distribution of interaction forces for both bacterial species, with the highest forces grouped at one pole of the cell for R. erythropolis 20S-E1-c and a random distribution of adhesion forces in the case of A. venetianus RAG-1. The magnitude of the adhesion forces was proportional to the three-phase contact angle between hexadecane and water on the bacterial surfaces.
微生物表面在分子水平上的结构和物理化学性质决定了它们与表面及界面的粘附。在此，我们报告了利用原子力显微镜（AFM）来探究水性缓冲液中柔软活细胞的形态、绘制细菌表面异质性图谱，并将AFM力-距离曲线中的结果与微生物表面的宏观性质直接关联起来。使用化学功能化的AFM探针探测了两种细菌——威尼斯不动杆菌RAG-1和红平红球菌20S-E1-c的表面，探针末端分别为疏水基团和亲水基团，这两种细菌表现出不同的宏观表面疏水性。所有力的测量均在接触模式下进行，并在从交流模式图像中选择的细菌位置上进行。AFM成像揭示了微生物表面超微结构的形态细节，分辨率约为20纳米。如回缩力曲线所示，异质表面形态与粘附力差异直接相关，并且如透射电子显微镜所证实的，还与外部结构（菌毛或荚膜）的存在相关。两种细菌的AFM力曲线均显示出细胞外结构与亲水和疏水探针相互作用的差异。威尼斯不动杆菌RAG-1呈现出不规则模式，有多个粘附峰，表明其表面存在不同长度的生物聚合物。红平红球菌20S-E1-c表现出长程吸引力和单次破裂事件，表明其表面更疏水且更光滑。粘附力测量表明，两种细菌的相互作用力在表面上呈斑块状分布，对于红平红球菌20S-E1-c，最高力集中在细胞的一极；而对于威尼斯不动杆菌RAG-1，粘附力呈随机分布。粘附力的大小与细菌表面上十六烷和水之间的三相接触角成正比。
