posted on 2021-10-07, 20:44authored byTingru Chang, R. Prasath Babu, Weijie Zhao, C. Magnus Johnson, Peter Hedström, Inger Odnevall, Christofer Leygraf
The mechanisms of
bacterial contact killing induced by Cu surfaces
were explored through high-resolution studies based on combinations
of the focused ion beam (FIB), scanning transmission electron microscopy
(STEM), high-resolution TEM, and nanoscale Fourier transform infrared
spectroscopy (nano-FTIR) microscopy of individual bacterial cells
of Gram-positive Bacillus subtilis in
direct contact with Cu metal and Cu5Zn5Al1Sn surfaces after high-touch
corrosion conditions. This approach permitted subcellular information
to be extracted from the bioinorganic interface between a single bacterium
and Cu/Cu5Zn5Al1Sn surfaces after complete contact killing. Early
stages of interaction between individual bacteria and the metal/alloy
surfaces include cell leakage of extracellular polymeric substances
(EPSs) from the bacterium and changes in the metal/alloy surface composition
upon adherence of bacteria. Three key observations responsible for
Cu-induced contact killing include cell membrane damage, formation
of nanosized copper-containing particles within the bacteria cell,
and intracellular copper redox reactions. Direct evidence of cell
membrane damage was observed upon contact with both Cu metal and Cu5Zn5Al1Sn
surfaces. Cell membrane damage permits copper to enter into the cell
interior through two possible routes, as small fragmentized Cu2O particles from the corrosion product layer and/or as released
copper ions. This results in the presence of intracellular copper
oxide nanoparticles inside the cell. The nanosized particles consist
primarily of CuO with smaller amounts of Cu2O. The existence
of two oxidation states of copper suggests that intracellular redox
reactions play an important role. The nanoparticle formation can be
regarded as a detoxification process of copper, which immobilizes
copper ions via transformation processes within the bacteria into
poorly soluble or even insoluble nanosized Cu structures. Similarly,
the formation of primarily Cu(II) oxide nanoparticles could be a possible
way for the bacteria to deactivate the toxic effects induced by copper
ions via conversion of Cu(I) to Cu(II).