Locally Enhanced Electric Field Treatment of E. coli: TEM, FT-IR and Raman Spectrometry Study

In this paper, we report the study of the low-voltage locally enhanced electric field treatment (LEEFT) of E. coli bacteria via TEM analysis and FT-IR and Raman spectrometry. The formation of pores was confirmed by TEM, which revealed the membrane rupture along with the formation of precipitates in the membrane and the cell volume, and by photoluminescence spectra of propidium iodide dye. LEEFT results in the alternation of DNA and RNA structure, indicated by the change in its α-helical and β-helical forms, decrease and narrowing of the nucleic acids-related IR and Raman peaks. Membrane damage is illustrated by the ambiguous character after low-voltage exposure: several membrane fatty acids’ peaks are broadening, while the others narrow, which indicates the overall change of the molecular bonds in their moiety, and may result from the rigidification during the shrinkage of the inner membrane and the increase in fluidity of the outer membrane. The corresponding fingerprints of cytochrome c and bo, located in the membrane or in the periplasm, on Raman spectra, reflect the arising changes in their structure and moiety. The observed changes were partially confirmed by TEM images, which indicate the dense precipitates’ formation in the cell volume and membrane, as well as the cytoplasmic membrane shrinkage away from the outer membrane.