Application of atomic force microscopy in bacterial research

Abstract

The atomic force microscope (AFM) has evolved from an imaging device into a multifunctional and powerful toolkit for probing the nanostructures and surface components on the exterior of bacterial cells. Currently, the area of application spans a broad range of interesting fields from materials sciences, in which AFM has been used to deposit patterns of thiol-functionalized molecules onto gold substrates, to biological sciences, in which AFM has been employed to study the undesirable bacterial adhesion to implants and catheters or the essential bacterial adhesion to contaminated soil or aquifers. The unique attribute of AFM is the ability to image bacterial surface features, to measure interaction forces of functionalized probes with these features, and to manipulate these features, for example, by measuring elongation forces under physiological conditions and at high lateral resolution (<1 A). The first imaging studies showed the morphology of various biomolecules followed by rapid progress in visualizing whole bacterial cells. The AFM technique gradually developed into a lab-on-a-tip allowing more quantitative analysis of bacterial samples in aqueous liquids and non-contact modes. Recently, force spectroscopy modes, such as chemical force microscopy, single-cell force spectroscopy, and single-molecule force spectroscopy, have been used to map the spatial arrangement of chemical groups and electrical charges on bacterial surfaces, to measure cell-cell interactions, and to stretch biomolecules. In this review, we present the fascinating options offered by the rapid advances in AFM with emphasizes on bacterial research and provide a background for the exciting research articles to follow.

Glyphosate-induced stiffening of HaCaT keratinocytes, a Peak Force Tapping study on living cells

“…Indeed, AFM based force spectroscopy is increasingly used to study the mechanisms of molecular recognition and protein folding/unfolding, to probe chemical groups and dynamics of receptor-ligand interactions (Florin et al 1994;Dorobantu and Gray, 2010;Rico et al, 2011), and to study the local elasticity (Clausen-Schaumann et al, 2000) and the mechanical properties of soft biological samples (Butt et al, 2005;Müller and Dufrene, 2008). The AFM has also provided nanometer-scale resolution imaging of biological samples ranging from single molecules, such as DNA (Hamon et al, 2007), to intact cells attached on biomaterials (Berquand et al, 2010).…”

Atomic force microscopy of a ctpA mutant in Rhizobium leguminosarum reveals surface defects linking CtpA function to biofilm formation

“…Atomic force microscopy (AFM) is the technique of choice to fully characterize the ultrastructure, physical and chemical properties of microbial surfaces (reviewed by Dorobantu & Gray, 2010). The ability to simultaneously probe and image viable specimens at high resolution offers a distinct advantage over scanning electron microscopy (Kaminskyj & Dahms, 2008).…”

Statistical Analysis of Long- and Short-Range Forces Involved in Bacterial Adhesion to Substratum Surfaces as Measured Using Atomic Force Microscopy

“…Surface thermodynamic analyses of bacterial cell and substratum surfaces using measured contact angles with liquids have not only indicated when thermodynamic conditions are favorable or unfavorable for adhesion (1, 37) but can also be employed in combination with measured zeta potentials of the interacting surfaces to determine the nature of the adhesion forces that mediate initial adhesion, i.e., the interplay among long-range (Lifshitz-van der Waals [LW] and electrical double-layer [EDL]) and short-range (Lewis acid-base [AB]) interaction forces (35). Surface thermodynamic analyses of bacterial adhesion have always been questioned, however, due to the macroscopic nature of the approach, among other concerns (10,14,15,17,32).While surface thermodynamic analyses are often viewed critically, atomic force microscopy (AFM) can also provide information on the nature of bacterial adhesion forces by means of Poisson analysis of the measured forces. AFM spectroscopy reveals the distance dependence of the adhesion force, and measured force-distance curves can be compared with theoretical models (3,7,8,13), which are usually based on the Derjaguin-Landau-Verwey-Overbeek (DLVO) theory (12, 39).…”

“…Surface thermodynamic analyses of bacterial cell and substratum surfaces using measured contact angles with liquids have not only indicated when thermodynamic conditions are favorable or unfavorable for adhesion (1,37) but can also be employed in combination with measured zeta potentials of the interacting surfaces to determine the nature of the adhesion forces that mediate initial adhesion, i.e., the interplay among long-range (Lifshitz-van der Waals [LW] and electrical double-layer [EDL]) and short-range (Lewis acid-base [AB]) interaction forces (35). Surface thermodynamic analyses of bacterial adhesion have always been questioned, however, due to the macroscopic nature of the approach, among other concerns (10,14,15,17,32).…”