Keywords: 
• nano-Fe⁰ /
• Escherichia coli /
• growth curves /
• enzymes activities /
• oxidative damage

Abstract: Cytotoxicity effects and mechanism of 20 nm nano-Fe⁰ on Escherichia coli were studied. In this paper, morphology of E. coli in the presence of nano-Fe⁰ was observed by transmission electron microscopy (TEM). E. coli cells were exposed to 0, 112, 560, 1 120 mg·L^-1 nano-Fe⁰ particles. Experiments were carried out to study the inhibitive effect of nano-Fe⁰ on E. coli growth. E. coli exposed to nano-Fe⁰ for 24 h, the activities of lactate dehydrogenase (LDH), cellular superoxide dismutase (SOD), malondialdehyde (MDA) were determined. Moreover, the influence of addition of N-Acetylcysteine (NAC) on the viability of cells was studied. TEM images of E. coli cells treated with nano-Fe⁰ exhibited significant disruption of the cell membranes. Experimental results of growth curves showed that nano-Fe⁰ nanoparticles could inhibit the growth of cells in liquid LB medium. Additionally, the shortened log phase and the prolonged stable phase of E. coli both resulted from the toxicity of nano-Fe⁰. Furthermore, the stable phase of E. coli is proportional to the concentration of nano-Fe⁰ particles. The activities of LDH and the levels of MDA significantly increased and there was a linear relationship between the concentration of nano-Fe⁰ and MDA levels, while the activities of SOD significantly decreased. To nano-Fe⁰-NAC exposure groups, the number of cell was higher than that of simple nanoFe⁰ exposure groups. The results demonstrated that oxidative damage was the mechanism of nano-Fe⁰ toxicity to E. coli.