Effects of Modified Magnetite Nanoparticles on Bacterial Cells and Enzyme Reactions

Current paper presents biological effects of magnetite nanoparticles (MNPs). Relations of MNP’ characteristics (zeta-potential and hydrodynamic diameters) with effects on bacteria and their enzymatic reactions were the main focus. Photobacterium phosphoreum and bacterial enzymatic reactions were chosen as bioassays. Three types of MNPs were under study: bare Fe(3)O(4), Fe(3)O(4) modified with 3-aminopropyltriethoxysilane (Fe(3)O(4)/APTES), and humic acids (Fe(3)O(4)/HA). Effects of the MNPs were studied at a low concentration range (< 2 mg/L) and attributed to availability and oxidative activity of Fe(3+), high negative surface charge, and low hydrodynamic diameter of Fe(3)O(4)/HA, as well as higher Fe(3+) content in suspensions of Fe(3)O(4)/HA. Low-concentration suspensions of bare Fe(3)O(4) provided inhibitory effects in both bacterial and enzymatic bioassays, whereas the MNPs with modified surface (Fe(3)O(4)/APTES and Fe(3)O(4)/HA) did not affect the enzymatic activity. Under oxidative stress (i.e., in the solutions of model oxidizer, 1,4-benzoquinone), MNPs did not reveal antioxidant activity, moreover, Fe(3)O(4)/HA demonstrated additional inhibitory activity. The study contributes to the deeper understanding of a role of humic substances and silica in biogeochemical cycling of iron. Bioluminescence assays, cellular and enzymatic, can serve as convenient tools to evaluate bioavailability of Fe(3+) in natural dispersions of iron-containing nanoparticles, e.g., magnetite, ferrihydrite, etc.