An in vivo study of electrical charge distribution on the bacterial cell wall by atomic force microscopy in vibrating force mode

Abstract

We report an in vivo electromechanical atomic force microscopy (AFM) study of charge distribution on the cell wall of Gram+ Rhodococcus wratislaviensis bacteria, naturally adherent to a glass substrate, under physiological conditions. The method presented in this paper relies on a detailed study of AFM approach/retract curves giving the variation of the interaction force versus distance between the tip and the sample. In addition to classical height and mechanical (as stiffness) data, mapping of local electrical properties, such as bacterial surface charge, was proved to be feasible at a spatial resolution better than a few tens of nanometers. This innovative method relies on the measurement of the cantilever's surface stress through its deflection far from (>10 nm) the repulsive contact zone: the variations of surface stress come from the modification of electrical surface charge of the cantilever (as in classical electrocapillary measurements) likely stemming from its charging during contact of both the tip and the sample electrical double layers. This method offers an important improvement in local electrical and electrochemical measurements at the solid/liquid interface, particularly in high-molarity electrolytes when compared to techniques focused on the direct use of electrostatic force. It thus opens a new way to directly investigate in situ biological electrical surface processes involved in numerous practical applications and fundamental problems such as bacterial adhesion, biofilm formation, microbial fuel cells, etc.

Bioelectricity, Its Fundamentals, Characterization Methodology, and Applications in Nano‐Bioprobing and Cancer Diagnosis

“…AFM has also been utilized to study the charge distribution on the Gram‐positive bacteria cell wall . The electromechanical approach can detect the potential between the tip (as the reference electrode) and the sample by measuring the cantilever's subtle deflection via surface stress.…”

Cell wall as a target for bacteria inactivation by pulsed electric fields

“…To fill this gap, we used multiparametric Atomic Force Microscopy (AFM) 13 a technique which allows the nanoscale observation of live single cells. AFM provided, height maps 14 , stiffness maps 15 and hydrophobicity maps by Chemical Force Microscopy 16 17 . Here, we performed nanoscale investigations of the damage induced by PEF-exposure in Bacillus pumilus , a non-pathogenic model of food contaminants like Clostridium difficile , Clostridium botulinum, Bacillus cereus 18 19 .…”

Optical interference probe of biofilm hydrology: label-free characterization of the dynamic hydration behavior of native biofilms

“…When a film is removed from the liquid in which it is immersed, the organism-friendly environment inside a biofilm is preserved in the interfering water-rich layer, which has a dielectric constant similar to that of the hydrated film. Since the dielectric constant of a material governs its response, i.e., the reorientation and redistribution of charge caused by an electric field, we suggest that the surface charge distribution of bacteria 36,37 is not perturbed when the bacteria traverse spatial regions with the same dielectric environment. Bacterial movement within and between the surrounding mostly aqueous liquid and the fully hydrated film is, therefore, facile and without physiological consequence.…”