Identification and characterization of anaerobic mercury-resistant bacteria isolated from mercury-polluted sediment

To develop biotechnology for biological treatment of mercury-contaminated wastes or for bioremediation of mercury-polluted sites, mercury-resistant microorganisms have been isolated and characterized. However, understanding of the mercury resistance mechanism by anaerobic bacteria is lacking. In this study, we tried to isolate anaerobic mercury-resistant bacteria from mercury-polluted sediment in Minamata Bay, Japan. One strain of the bacterial isolates, designated Mersaru, was used for the identification and for the growth capability of mercurials. We also analyzed genetic characteristics of mercury resistance genes (merA and merB gene) from the strain Mersaru. The strain Mersaru, which was isolated from Minamata Bay sediment, was identified as Clostridium butyricum and showed resistance to both inorganic mercury and organomercurials. Furthermore, nucleotide sequence analysis showed that merA and merB genes of the strain Mersaru were identical to those of the B. cereus RC607 an aerobic mercury-resistant bacterium in the nucleotide sequence level. From the pulsed field gel electrophoresis analysis, it is suggest that the mer operon of the strain Mersaru is located on chromosomal DNA.