Probing Microbial Cell Surface Charges by Atomic Force Microscopy

Abstract

Most microorganisms possess a negative surface charge under physiological conditions due to the presence of anionic carboxyl and phosphate groups. Cell surface charge plays an important role in controlling cell adhesion and aggregation phenomena, as well as antigen−antibody, cell−virus, cell−drug, and cell−ions interactions. We have used atomic force microscopy (AFM) with chemically functionalized probes to investigate the surface charges of yeast cells. Force−distance curves and adhesion maps recorded with probes terminated with ionizable carboxyl groups were strongly influenced by pH: while no adhesion was measured at neutral/alkaline pH, multiple adhesion forces were recorded at pH ≤ 5. Three pieces of evidence indicated that these changes were related to differences in the ionization state of the cell surface functional groups. First, the adhesion force vs pH curve was correlated with microelectrophoresis data, the pH of the largest adhesion force corresponding to the cell isoelectric point, i.e., pH 4. Second, treating the cells with Cu(II) ions caused a reversal of the cell surface charge at neutral pH and promoted the adhesion toward the negatively charged probe. Third, control experiments using nonionizable hydroxyl-terminated probes indicated that the changes in adhesion forces were not simply due to the titration of the probe surface charges. This study shows that AFM with chemically modified probes is a valuable approach in microbiology and biophysics for probing the local electrostatic properties of microbial cell surfaces.

Scanning electrochemical microscopy of menadione-glutathione conjugate export from yeast cells

“…Under physiological conditions, S. cerevisiae cells have a negatively charged cell surface (35), where surface macromolecules, such as mannoproteins and glucan that contain phosphodiester, amino, and carboxyl groups, produce charge on the cell that aids in adhesion processes (36). Yeast cells can therefore be immobilized on glass supports that have been pretreated with poly(L-lysine).…”

Antibacterial activity and mode of action of selected glucosinolate hydrolysis products against bacterial pathogens

“…carboxyl and phosphate) in their membranes (Gilbert et al 1991;Lerebour et al 2004;Palmer et al 2007). However, the magnitude of the charge varies from species to species and can be influenced by various conditions, namely age of the culture, ionic strength and pH (Ahimou et al 2002;Palmer et al 2007). Zeta potential measurements demonstrated that after ITCs exposure, the cells become less negatively charged.…”

Force measurements with the atomic force microscope: Technique, interpretation and applications

“…The density of the thiols or disulfides on the gold surface is well determined, and as a result forces between defined chemical groups can be measured [120]. Various rest groups have been used such as carboxyl (-COOH) [121], hydroxyl (-OH) [122], methyl (-CH 3 ), acetate (-OCOCH 3 ) [123,124], amide [125], and amino [126,127]. One problem of chemically modified tips is that they might be destroyed by the interaction with another surface.…”

“…A way of measuring the force between two surfaces with a well-defined density of functional groups is to coat the tip with thiols or disulfides. Titration experiments have been done with a number of differently coated surfaces [121,122,[124][125][126][127].…”