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 antim- icrobial 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 mi- croscopy (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 antimicro- bial 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). 1.1 Strains and reagents The strain of E. coli (8099) was provided by Microbial Culture Collection Center of Guang- dong Institute of Microbiology. Ce(NO3)3·6H2O (AR) was obtained from Sinopharm Chemical Reagent Co., Ltd. The LB culture contained NaCl 1.0 g, tryptone 1.0 g and yeast extract 0.5 g per 100 ml (pH=7.0). The LB agar culture con- tained agar 1.5 g per 100 ml LB culture. The Ce(NO3)3·6H2O stocking solution contained 1.0×10 4 mg Ce(NO3)3·6H2O per