Roles of membrane protein damage and intracellular protein damage in death of bacteria induced by atmospheric-pressure air discharge plasmas

Although plasma sterilization has attracted much attention, the underlying mechanisms and biochemical pathways are still not fully understood. In this work, we investigate the molecular mechanism pertaining to the inactivation of <i>Escherichia coli</i> (<i>E. coli</i>) by air discharge plasmas. The membrane protein <i>YgaP</i> and intracellular protein <i>swc7</i> are over-expressed in <i>E. coli</i> by genetic recombination and gene inducible expression techniques and plasma exposure is demonstrated to alter the structures of <i>YgaP</i> and <i>swc7</i> in <i>E. coli</i>. The plasma-induced damage of <i>YgaP</i> and <i>swc7</i> involves changes in the secondary and tertiary structures instead of the primary structure and the modification effectiveness depends on the storage time after the plasma treatment. Owing to the unique structure of <i>E. coli</i>, <i>YgaP</i> is more susceptible to the plasma treatment than intracellular <i>swc7</i>. Within 1 h after plasma exposure, <i>YgaP</i> is modified but not <i>swc7</i>, but after 1 h or longer, both <i>YgaP</i> and <i>swc7</i> proteins are indeed modified. By analyzing the plasma-induced antimicrobial efficacy and modification of <i>YgaP</i> and <i>swc7</i>, plasma-induced modification of the membrane proteins is the major cause of bacterial death but there is no identifiable relationship with modification of the intracellular protein. The new results provide insights into the mechanism of multiple plasma-induced damage to bacteria and cells as well as the disinfection mechanism.