As shown in Fig 8, when E. coli was exposed to different concentrations of MSNs, the perturbed metabolites were mainly concerned with protein biosynthesis, glycine, serine and threonine metabolism, the urea cycle, phenylalanine and tyrosine metabolism, ammonia recycling, methionine metabolism, and the electron transport chain. Interestingly, four functions, namely protein biosynthesis, glycine, serine and threonine metabolism, urea cycle, and methionine metabolism, were significantly changed in all the experimental groups. These results suggested that MSNs mainly affect protein biosynthesis and the amino acid metabolism of E. coli.