Abstract
Heavy metals pollution represents an important environmental problem. One of these metals is mercury. The aim of this research was isolating bacteria highly resistant to mercury from dental clinic effluent to investigate their growth potential in the presence of other heavy metals, such as Zn, Cu, Ni, Ag, Cd and Pb. Three dental wastewater samples were selected and their mercury concentrations, pH, EC, BOD5 and COD were determined. The mercury-resistant bacteria were found to belong to the genera of Pseudomonas, Proteus, Citrobacter, Bacillus, Corynebacterium and Staphylococcus. In examining multi-metal resistances, the pattern of hexa-R was seen in the case of Citrobacter and Pseudomonas genera. The highest tolerated concentration of heavy metals was 25.6 mM which is related to Ag and Cu and tolerated by Citrobacter isolate. It is also indicated that Citrobacter was the most resistant isolates to Cd with significant difference (P < 0.05). Results of this study demonstrate the occurrence of different groups of bacteria, capable of high tolerance to mercury with a potential to tolerate a variety of other toxic heavy metals suggest that, resistance to many types of toxicants may be present in the same organism; therefore, such organisms have high potential for biotechnology purposes. Key words: Bacteria, dental effluent, heavy metal, mercury, multi-metal resistance.
Highlights
Heavy-metals are widely used in chemistry and engineering
The mercury-resistant bacteria were found to belong to the genera of Pseudomonas, Proteus, Citrobacter, Bacillus, Corynebacterium and Staphylococcus
Results of this study demonstrate the occurrence of different groups of bacteria, capable of high tolerance to mercury with a potential to tolerate a variety of other toxic heavy metals suggest that, resistance to many types of toxicants may be present in the same organism; such organisms have high potential for biotechnology purposes
Summary
Heavy-metals are widely used in chemistry and engineering. There is increasing interest in the biotechnology of extraction of rare metals from primary and secondary raw materials (Korenevskii et al, 1997). The discharge of heavy metals into the environment as a result of agricultural, industrial and military operations, and the effects of this pollution on ecosystems and human health have been of concern for some years (Essa et al, 2002). These heavy metals include cadmium, chromium, cobalt, manganese, mercury, nickel, silver, and zinc. Microbial populations in metal-polluted environments contain microorganisms that have adapted to the toxic concentrations of heavy metals and become “metal resistant” (Leung and Chua, 2001)
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