Responsibility of Hydrogen Peroxide for the Lethality of Resting Escherichia coli B Cells Exposed to Alternating Current in Phosphate Buffer Solution

Surviving fractions of Escherichia coli B exposed to an alternating current (AC) of 50 Hz in a phosphate buffer solution of pH 7.0 at 29°C were closely related to the amount of H₂O₂ formed in cell suspensions. At a definite current density, the amount of H₂O₂ in the suspensions or in buffer solution without cells increased with increasing AC-exposure time under aerobic conditions. On the other hand, the formation of H₂O₂ on AC-exposure was not detected under anaerobic conditions. It was considered that H₂O₂ was formed on the surface of carbon electrodes by AC-electrolytic reduction of dissolved oxygen. The amount of H₂O₂ formed decreased with increasing concentration of cells suspended or of catalase added to the suspension. When the formation of H₂O₂ was significantly suppressed, surviving fractions of cells exposed to AC remained almost unchanged. Growth conditions, modifying the intracellular level of catalase of E. coli, affected the sensitivity of cells to AC-exposure.