Bacterial
extracellular polymeric substances (EPS) have been recently
found to contribute most for metal removal in nanoenhanced bioremediation.
However, the mechanism by which NPs affect EPS–metal interactions
is not fully known. Here, Halomonas sp. was employed
to explore the role of EPS after in vivo exposure to Cd/Pb and polyvinylpyrrolidone
(PVP) coated iron oxide nanoparticles (IONPs, 20 mg L–1) for 72 h. Cd–IONPs produced the highest concentrations of
EPS proteins (136.3 mg L–1), while Cd induced the
most production of polysaccharides (241.0 mg L–1). IONPs increased protein/polysaccharides ratio from 0.2 (Cd) to
1.2 (Cd–IONPs). The increased protein favors the formation
of protein coronas on IONPs surface, which would promote Cd adsorption
during NP–metal–EPS interaction. FTIR analysis indicated
that the coexistence of Cd and IONPs interacted with proteins more
strongly than with polysaccharides. Glycosyl monomer analyses suggested
mannose and glucose as target sugars for EPS complexation with metals,
and IONPs reduced metal-induced changes in monosaccharide profiles.
Protein secondary structures changed in all treatments, but we could
not distinguish stresses induced by metals from those by IONPs. These
findings provide greater understanding of the role of EPS in NP–metal–EPS
interaction, providing a better underpinning knowledge for the application
of NP-enhanced bioremediation.