<i>In vivo</i> atomic force microscopy–infrared spectroscopy of bacteria

Abstract

A new experimental platform for probing nanoscale molecular changes in living bacteria using atomic force microscopy-infrared (AFM-IR) spectroscopy is demonstrated. This near-field technique is eminently suited to the study of single bacterial cells. Here, we report its application to monitor dynamical changes occurring in the cell wall during cell division in <i>Staphylococcus aureus</i> using AFM to demonstrate the division of the cell and AFM-IR to record spectra showing the thickening of the septum<i>.</i> This work was followed by an investigation into single cells, with particular emphasis on cell-wall signatures, in several bacterial species. Specifically, mainly cell wall components from <i>S. aureus</i> and <i>Escherichia coli</i> containing complex carbohydrate and phosphodiester groups, including peptidoglycans and teichoic acid, could be identified and mapped at nanometre spatial resolution. Principal component analysis of AFM-IR spectra of six living bacterial species enabled the discrimination of Gram-positive from Gram-negative bacteria based on spectral bands originating mainly from the cell wall components. The ability to monitor <i>in vivo</i> molecular changes during cellular processes in bacteria at the nanoscale opens a new platform to study environmental influences and other factors that affect bacterial chemistry.