Biosorption of Some Heavy Metals from Media with High Salt Concentrations by Halophilic Archaea

Heavy metal pollution represents an important environmental problem due to the toxic effects of metals. Their accumulation throughout the food chain leads to serious ecological and health problems. The remediation of environments metal contaminated through physico-chemical methods present major disadvantages such as high energy consumption, high costs and incomplete removal of metal ions. Biosorption of heavy metals by microorganisms is an alternative method that involves low costs. Active elimination process of heavy metals ions provided by living cells, especially by their components and extracellular products represent a potential way of removing toxic heavy metals from industrial wastewaters. Extremely halophilic archaea require high salt concentrations for growth and inhabit hypersaline environments (solar salterns, salt lakes and salt mines), where the NaCl concentration exceeds 200 250g l-1 or reaches saturation. Frequently, hypersaline environments are contaminated with toxic compounds. Therefore, the search of microorganisms able to degrade toxic agents in the presence of high salt concentrations appears to be desirable, especially for biological treatment of highly saline industrial waste effluents. Also, some metal-resistant halophilic microorganisms could be used as indicator organisms in saline polluted environments. The aim of this study was to determine the metal tolerance levels of some collection and wild haloarcheal strains from Haloferax genus. Also, we study the capacity of tested strains to reduce the concentration of some heavy metals from media with high salt concentration by biosorption process involved extracellular polysaccharides. The results showed that the wild strain has a higher susceptibility to Zn ion comparatively with the collection strain. The growth of tested strains and their capacity to removal of metal ions were stimulated by the addition of glucose at culture medium. Thus, the synthesis of exopolysaccharides enhanced the reduction activity of Cr, Zn and Ni concentrations by the haloarcheal investigated strains.