Abstract
Nickel nanoparticles (NPs) are used for soil remediation and wastewater treatment due to their high adsorption capacity against complex organic pollutants. However, despite the growing use of nickel NPs, their toxicological towards environmental bacteria have not been sufficiently studied. Actinobacteria of the genus Rhodococcus are valuable bioremediation agents degrading a range of harmful and recalcitrant chemicals. Both positive and negative effects of metal ions and NPs on the biodegradation of organic pollutants by Rhodococcus were revealed, however, the mechanisms of such interactions, in addition to direct toxic effects, remain unclear. In the present work, the influence of nickel NPs on the viability, surface topology and nanomechanical properties of Rhodococcus cells have been studied. Bacterial adaptations to high (up to 1.0 g/L) concentrations of nickel NPs during prolonged (24 and 48 h) exposure were detected using combined confocal laser scanning and atomic force microscopy. Incubation with nickel NPs resulted in a 1.25–1.5-fold increase in the relative surface area and roughness, changes in cellular charge and adhesion characteristics, as well as a 2–8-fold decrease in the Young’s modulus of Rhodococcus ruber IEGM 231 cells. Presumably, the treatment of rhodococcal cells with sublethal concentrations (0.01–0.1 g/L) of nickel NPs facilitates the colonization of surfaces, which is important in the production of immobilized biocatalysts based on whole bacterial cells adsorbed on solid carriers. Based on the data obtained, cell surface functionalizing with NPs is possible to enhance adhesive and catalytic properties of bacteria suitable for environmental applications.
Highlights
According to the confocal laser scanning microscope (CLSM) data (Figure 1), the viability of Rhodococcus strains decreased as a result of incubation with Ni NPs, depending on the concentration of nanoparticles and incubation time
Treatment with medium (0.01–0.1 g/L) concentrations of NPs resulted in 55–70% of cell survival. Such differences in rhodococcal resistance to metal NPs can be explained by their physiological peculiarities. It was previously shown [12] that representatives of R. ruber and R. rhodochrous synthesizing red-orange non-diffusing pigment were more resistant to heavy metal ions, in particular Ni2+, compared with non-pigmented Rhodococcus species
The concentration-dependent effects of nickel NPs on the viability, surface topology and mechanical properties of Rhodococcus cells suggested the possibility of their nanomodification with selected nanometal concentrations in order to improve adhesive and hydrocarbon-degrading activities
Summary
Despite the growing use and accumulation of nickel nanoparticles (NPs) in the environment, the toxicological aspects of their effects on living organisms, in particular bacterial cells, have not been sufficiently studied [2,3]. Actinobacteria of the genus Rhodococcus degrade a number of harmful and persistent chemicals, such as petroleum hydrocarbons, phenols, solvents, pesticides and pharmaceutical pollutants and, are used in bioremediation [10,11]. They are characterized by Nanomaterials 2022, 12, 951. A number of studies have shown both positive and negative effects of metal ions and NPs on the biodegradation of organic pollutants by rhodococci [13–15]; the mechanisms of such effects, in addition to the direct toxic effects of NPs on bacterial cells, remain unclear
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