Molecular Analysis of merA Gene Possessed by Anaerobic Mercury-Resistant Bacteria Isolated from Sediment of Minamata Bay

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To understand the molecular basis of the mercury resistance of anaerobic bacteria, twenty-six mercury-resistant bacterial strains were anaerobically isolated from the mercury-polluted sediment of Minamata Bay, Japan. On the basis of taxonomic characteristics, all of the isolates were classified into the genus Clostridium. PCR primers designed from the core sequence of the merA genes that are involved in the inorganic mercury reduction by the aerobic mercury-resistant bacteria were used for the molecular analysis. Southern hybridization analysis confirmed that the PCR products amplified from the chromosomal DNA of the twenty-six Clostridium isolates were highly homologous to the merA gene of an aerobic mercury-resistant Gram-positive bacterium, Bacillus sp. RC607. Furthermore, the DNA sequence of the PCR product amplified from one of the isolates is 99.7% identical to the corresponding region of the merA gene of Bacillus sp. RC607. These results suggest that the same mercury resistance system developed by aerobic mercury-resistant bacteria is acquired by the anaerobic mercury-resistant bacteria.