Multi-metal resistance study of bacteria highly resistant to mercury isolated from dental clinic effluent

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.