The “Protein Corona” of Silver-Sulfide Nanoparticles Obtained Using Gram-Negative and -Positive Bacteria

A comparative analysis of the amount and composition of the proteins adsorbed onto the surface of silver-sulfide (NpAg₂S) nanoparticles obtained by biosynthesis using bacteria was carried out for the first time. These were the gram-negative bacteria Shewanella oneidensis MR-1 and Escherichia coli K12, as well as the gram-positive bacterium Bacillus subtilis 168. The biosynthesis of NpAg₂S was carried out in nutrient broth with 1 mM of AgNO₃ and Na₂S₂O₃ · 5H₂O salts in the presence of bacterial cells under aerobic conditions. Analysis of NpAg₂S by transmission electron microscopy showed that the particles were spherical and had an average diameter of 8 ± 2 nm for S. oneidensis MR-1 and E. coli K12 and 10 ± 3 nm for B. subtilis 168. It was found that the highest amount of protein was sorbed on NpAg₂S, when the strain B. subtilis 168 was used, and the smallest amount was sorbed by E. coli. The main proteins adsorbed on NpAg₂S were determined by the MALDI TOF/TOF method, and the heterogeneity of the protein coating was revealed. The lowest heterogeneity of proteins on the surface of nanoparticles is observed in the case of B. subtilis (only one protein, flagellin, predominates); the highest heterogeneity of proteins was found on nanoparticles obtained using S. oneidensis MR-1. All proteins covering the surface of NpAg₂S were shown to be outer-membrane or cytoplasmic-membrane proteins of the studied bacteria. The composition of the protein coating of nanoparticles is individual and constant for each bacterial strain used. The values of the ζ-potential and the effective diameter of nanoparticles were shown to differ depending on the “protein corona” of the strain that was used to obtain NpAg₂S. The characteristic of the “protein corona” of biologically obtained nanoparticles is an important and necessary condition for their practical application.