Synchrotron FTIR spectroscopy reveals molecular changes in Escherichia coli upon Cu2+ exposure

Copper ions (e.g., Cu2+) have outstanding antibacterial properties, but the exact mechanism is rather complex and not fully understood. In this work, synchrotron Fourier transform infrared (FTIR) spectroscopy was used as an analytical tool to investigate the CuCl2-induced biochemical changes in Escherichia coli. Our spectral measurements indicated that this technique is sensitive enough to detect changes in membrane lipids, nucleic acids, peptidoglycans and proteins of Cu2+-treated bacteria. Interestingly, for short-time treated cells, the effects on phospholipid composition were clearly shown, while no significant alterations of proteins, nucleic acids and peptidoglycans were found. PeakForce quantitative nano-mechanics mode atomic force microscopy (AFM) confirmed the changes in the topography and mechanical properties of bacteria upon the Cu2+ exposure. This study demonstrated that FTIR spectroscopy combined with AFM can provide more comprehensive evaluation on the biochemical and mechanical responses of bacteria to copper.