Characteristics of Hg-resistant bacteria isolated from Minamata Bay sediment

Seventy-two strains of Hg-resistant bacteria ( Pseudomonas) were isolated on agar plates containing 40 μg/ml of HgCl 2 from Minamata Bay sediment, which was heavily polluted with mercury (45.8 μg/g). The minimal inhibitory concentrations (MICs) of mercurial compounds were determined for the Hg-resistant pseudomonads and 65 strains ( Pseudomonas sp., Bacillus sp., Vibrio sp., and Corynebacterium sp.) isolated from Sendai Bay sediment (1 μg/g of mercury) as control. The MICs to HgCl 2, CH 3HgCl, C 2H 5HgCl, C 3H 7HgCl, and C 6H 5HgOCOCH 3 for the Hg-resistant pseudomonads from Minamata Bay were significantly higher than those of strains from Sendai Bay. The volatilization from liquid culture containing 20 μg/ml of HgCl 2 was observed in all of the Hg-resistant pseudomonads from Minamata Bay (70 strains). The mean loss of mercury from liquid culture was 60.4 ± 17.3%. Further study is warranted to determine what role the Hg-resistant bacteria, particularly the Pseudomonas species, play in the mercury cycle in Minamata Bay.