Abstract
Nanoparticles and bacteria have received a great attention worldwide due to their ability to remove heavy metals (HMs) from wastewater. The current study is aimed at finding the interaction of HMs-resistance strains ( Bacillus cereus and Lysinibacillus macroides) with different concentrations (5, 10, 15, 20, and 25 mg/L) of zinc oxide nanoparticles (ZnO NPs) and how they would cope with HM stress (Pb, Cd, Cr, and Cu). The growth rate and tolerance potential of bacteria were increased at lowered concentrations (5 and 10 mg/L) of ZnO NPs against HMs while it was unaffected at higher concentrations of ZnO NPs. These findings were confirmed by minimum inhibition zone and higher zinc solubilization at lower concentrations of ZnO NPs. Scanning electron microscopy (SEM) revealed that higher concentrations of ZnO NP increased HM accumulation in bacteria cells which had a significant impact on bacterial morphology and caused pores in bacterial membrane while in the case of lower concentrations, the cell remained unaffected. These results were further supported by the less production of antioxidant enzymes (SOD, POD, and CAT), thiobarbituric acid reactive substances (TBARS), and hydrogen peroxide (H2O2) contents at lower concentrations of ZnO NPs against heavy metal stress. This study suggested that synergistic treatment of Bacillus spp. with lower concentrations of ZnO NPs enhances the tolerance potential and significantly reduces the HM toxicity.
Highlights
Various methods such as ion exchange, metal precipitation, adsorption methods, and reverse osmosis were used in the past for the removal of heavy metals (HMs) but these methods were ineffective, costly, and time-consuming [1, 2]
zinc oxide nanoparticles (ZnO NPs) were characterized by Amara et al [13] through Field Emission Scanning Electron Microscope (FESEM), Transmission Electron Microscopy (TEM), Fourier Transform Infrared Spectroscopy (FTIR), and X-ray diffraction (XRD)
We see whether ZnO NPs can increase bacteria’s resistance against different HMs
Summary
Various methods such as ion exchange, metal precipitation, adsorption methods, and reverse osmosis were used in the past for the removal of HMs but these methods were ineffective, costly, and time-consuming [1, 2]. After that, microbebased remediation was used to remove heavy metal stress. Bacteria have different detoxifying mechanism, such as biosorption, bioaccumulation, biotransformation, and biomineralization to alleviate the HM stress [3]. Solubilized state of HMs is not quickly and effectively removed by bacteria [4]. There was a great demand to use adsorbents, which have efficient heavy metal binding capabilities and help in the removal of HMs. ZnO
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