Dissociation of outer membrane for Escherichia coli cell caused by cerium nitrate

The biological effect of cerium nitrate on the outer membrane (OM) of Escherichia coli (E. coli) cell was studied, and the antimicrobial mechanism of rare earth elements was explored. The antimicrobial effect of cerium nitrate on E. coli cell was valued by plate count method, and the morphology change of E. coli cell was observed with scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The results showed that the E. coli cell suspension was flocculated when the concentration of Ce(NO₃)₃·6H₂O solution was greater than or equal to 100 mg/L, which may be due to the alteration of charge and hydrophobicity of the E. coli cell surface. The antimicrobial assay suggested that 100 mg/L Ce(NO₃)₃·6H₂O solution could kill 80.69% of E. coli cells, and the killing rate reached nearly 99% at 1000 mg/L. The antimicrobial target site of rare earth elements was observed on the cell wall in SEM and TEM images. With the concentration of Ce(NO₃)₃·6H₂O solution increasing, the OM of E. coli cell was separated (≤100 mg/L), dissociated (100～500 mg/L) or even departed (≥500 mg/L) from cytoplasmic membrane (CM).