Adaptations of Escherichia coli K\n12 to Synchrotron Sourced THz Radiation

The biological effects\nof electromagnetic field (EMF) irradiation\nin the terahertz (THz) range remain ambiguous, despite numerous studies\nthat have been conducted. In this paper, the metabolic response of Escherichia coli K 12 to EMF irradiation was examined\nusing a 1.0 W m<sup>–2</sup> incident synchrotron source (SS)\nin the range of 0.5–18.0 THz for over 90 min of continuous\nexposure at 25 °C. This continuous SS THz exposure induced periodic\ndecreases in the cell growth after 10, 20, and 40 min of exposure\ncompared to a time-matched control; however, the number of viable\ncells thereafter grew. The physiological status of treated cells immediately\nafter exposure was assessed by using the direct plate counting technique\nand electron microscopy. Analysis of scanning electron microscopy\n(SEM) and high-resolution cryogenic transmission electron (cryo-TEM)\nmicrographs showed that approximately 20% of the SS THz-exposed E. coli cells exhibited a deformed outer membrane,\nmembrane perturbations, and leakage of cytosol. The proteome changes\nin E. coli cells after 18 h postexposure\nwere associated with cellular response to plasma membrane regulation\nincluding phospholipid biosynthetic process and osmotic stress. The\nresults of this study highlighted that E. coli cells can promptly activate the fundamental mechanisms in response\nto prolonged exposure to THz radiation that are evolutionarily developed\nto withstand other environmental stressors.