Isolation and characterization of halophilic bacteria with the ability of heavy metal bioremediation and nanoparticle synthesis from Khara salt lake in Iran

Increasing environmental pollutants such as heavy metals have become one of the most severe health dangers because of rapid industrialization. Exposure to lead and nickel heavy toxic metals can lead to hazardous diseases affecting most of the organs in humans. Bioremediation is a process that uses the ability of microorganisms or plants to detoxify environmental contaminants at lower costs than physicochemical techniques. This study isolated halophilic bacteria from Khara salt lake in Iran and screened their ability to resist lead and nickel. After screening stages, three selected strains including Bacillus sp. A21, Oceanobacillus sp. A22 and Salinicoccus A43 were identified by16S rDNA sequencing and the related sequences were submitted to GeneBank with accession IDs MN588312, MN588313, and MN 588,314, respectively. These strains resist 7.2 mM, 4.1 mM, and 6.7 mM lead and 3.6 mM, 3.7 mM, and 4.1 mM nickel, respectively. Investigation of growth pattern and evaluation of bioremediation ability by atomic absorption spectroscopy revealed that Bacillus sp. A21 could decrease lead and nickel in culture medium up to 97.5% and 76%, respectively. Oceanobacillus sp. A22 showed higher lead bioremediation rate (98.8%) and lower nickel-bioremediation rate (73.5%). Salinicoccus sp. A43 showed the least bioremediation ability (92% lead and 71.7% nickel). The ability of selected strains to synthesize lead and nickel nanoparticles was evaluated using UV/Vis spectrophotometry and Energy-Dispersive X-ray Spectroscopy (EDX). Particle dimensions were measured using Scanning Electron Microscopy (SEM). Bacillus sp. A21 and Oceanobacillus sp. A22 strains were able to synthesize lead nanoparticles; however, Salinicoccus sp. A43 could synthesize both lead and nickel nanoparticles.