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Abstract
The use of metal-based and, particularly, Al2O3 nanoparticles (Al2O3-NP) for diverse purposes is exponentially growing. However, the growth of such promissory market is not accompanied by a parallel extensive investigation related to the impact of this pollution on groundwater and biological systems. Pseudomonas species, ubiquitous, environmentally critical microbes, frequently respond to stress conditions with diverse strategies that generally include extracellular polymeric substances (EPS) formation. The aim of this study is to report that changes in the aqueous environment, particularly, the addition of Al2O3-NP without and with humic acids, induce different adaptive strategies of Pseudomonasaeruginosa early biofilms. To this purpose, early biofilms were incubated in diluted culture media without (control) and with Al2O3-NP, and with humic acids (HA-control, HA-Al2O3-NP) for 24h. 3D colonies with EPS strings and isolated bacteria in their surroundings were detected in the control biofilms. Unlikely, an unusual adaptive behaviour was developed in the presence of Al2O3-NP. Bacteria opt to disassemble the 3D arrangements and to implement a 2D network promoting morphological and size changes of bacterial cells (small coccoid shapes). Remarkably, this strategy allows their temporarily non-EPS-depending survival without decreasing the number of cells. This behaviour was not observed with ZnO-NP, HA-Al2O3-NP, or HA-ZnO-NP. Physicochemical analysis revealed that HA were adsorbed on Al2O3-NP and promoted the Al(III) ions complexation. This supports the hypothesis that the reduction of toxicity of Al ions and the 3D colony formation in the presence of HA-Al2O3-NP is promoted by the complexation of the metal ions with HA components.
Highlights
Production of the engineered nanoparticles (NP) is growing exponentially due to their multiple applications
The aim of this study is to report that changes in the aqueous environment, the addition of Al2O3-NP without and with humic acids, induce different adaptive strategies of P. aeruginosa early biofilms
The glass samples with the early biofilms were placed in a multiwell, the diluted culture medium (DCM) was added, and the biofilm was following incubated for 24h
Summary
Production of the engineered nanoparticles (NP) is growing exponentially due to their multiple applications. Our understanding on the environmental fate and effects of these nanoproducts is far from being complete. There are several important factors to be considered in relation to groundwater contamination by NP, among them: release of metal ions by NP, surface reactions with organic components of aquatic media and NP impact in the biological environment [1]–[4]. Among metal oxide NPs, aluminium oxide NP (Al2O3-NP) are widely used. Considering the possible future expansion of this particular NP market, their impact under different natural exposure scenarios where Alcontaining NP can accumulate deserves a special attention since they may affect biological ecosystems [5]–[7],
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