K. Iwahori et al., Ferrous iron-dependent volatilization of mercury by the plasma membrane ofThiobacillus ferrooxidans, APPL ENVIR, 66(9), 2000, pp. 3823-3827
Of 100 strains of iron-oxidizing bacteria isolated, Thiobacillus ferrooxida
ns SUG 2-2 was the most resistant to mercury toxicity and could grow in an
Fe2+ medium (pH 2.5) supplemented with 6 mu M Hg2+. In contrast, T. ferroox
idans AP19-3, a mercury-sensitive T. ferrooxidans strain, could not grow wi
th 0.7 mu M Hg2+. When incubated for 3 h in a salt solution (pH 2.5) with 0
.7 mu M Hg2+, resting cells of resistant and sensitive strains volatilized
approximately 20 and 1.7%, respectively, of the total mercury added. The am
ount of mercury volatilized by resistant cells, but not by sensitive cells,
increased to 62% when Fe2+ was added. The optimum pH and temperature for m
ercury volatilization activity were 2.3 and 30 degrees C, respectively. Sod
ium cyanide, sodium molybdate, sodium tungstate, and silver nitrate strongl
y inhibited the Fe2+-dependent mercury volatilization activity of T, ferroo
xidans. When incubated in a salt solution (pH 3.8) with 0.7 (mu M Hg2+ and
1 mM 1 Fe2+ plasma membranes prepared from resistant cells volatilized 48%
of the total mercury added after 5 days of incubation. However, the membran
e did not have mercury reductase activity with NADPH as an electron donor.
Fe2+-dependent mercury volatilization activity was not observed with plasma
membranes pretreated with 2 mM sodium cyanide. Rusticyanin from resistant
cells activated iron oxidation activity of the plasma membrane and activate
d the Fe2+-dependent mercury volatilization activity of the plasma membrane
.