Ferrous Iron-Dependent Volatilization of Mercury by the Plasma Membrane of Thiobacillus ferrooxidans

Abstract

Of 100 strains of iron-oxidizing bacteria isolated, Thiobacillus ferrooxidans SUG 2-2 was the most resistant to mercury toxicity and could grow in an Fe 2؉ medium (pH 2.5) supplemented with 6 M Hg

Volatilization of Mercury by an Iron Oxidation Enzyme System in a Highly Mercury-resistantAcidithiobacillus ferrooxidansStrain MON-1

“…It has been known that A. ferrooxidans cells are in general resistant to many heavy metals including iron, copper, zinc, and nickel, but sensitive to mercury, silver, molybdenum, and tungsten. [4][5][6][7][8][9][10] We have reported the growth inhibition of A. ferrooxidans cells by mercury, silver, molybdenum, and tungsten and clariˆed inhibition sites for these toxic metals. [7][8][9][10][11] Among these toxic metals mercury is highly toxic for almost all organisms because they have a strong a‹nity for thiol groups in proteins.…”

Reduction of Hg2+with Reduced Mammalian Cytochromecby CytochromecOxidase Purified from a Mercury-ResistantAcidithiobacillus ferrooxidansStrain, MON-1

“…The other is the ferrous ion-dependent mercury reducing system. [30][31][32] The latter Hg 0 volatilization system is unique among the mercury detoxification systems reported for microorganisms to date. From the results obtained previously, it was supposed that the Fe 2þ -dependent mercury reductase system plays a role when strains SUG 2-2 and MON-1 grow in ferrous iron medium (pH 2.5) supplemented with a high concentration of Hg 2þ , probably more than 5.0 mM, 30) but the important question which of the components in the iron oxidation enzyme system is involved in the mercury reduction remains unsolved.…”

“…We have reported on the isolation of five physiologically different A. ferrooxidans strains, and have stressed importance of cytochrome c oxiase on cells' physiological differences. 10,[30][31][32]36,37) A. ferrooxidans strain Funis 2-1 is resistant to molybdenum (Mo 5þ ), strains Funis 2-1 and SUG 2-2 to mercury, strain OK1-50 to sulfite ion, and strain NASF-1 to 2,4-dinitrophenol. In contrast, A. ferrooxidans strain AP19-3 is sensitive to all these toxic compounds.…”

“…32,[35][36][37][38][39][40][41][42][43][44] We have found that mercury resistant-A. ferrooxidans strains SUG 2-2 and MON-1 have high Fe 2þ -dependent mercury volatilization activity in the cells, 30,31) and that cytochrome c oxidase purified from strain SUG 2-2 reduces Hg 2þ with Fe 2þ as electron donor volatilizing metalic mercury (Hg 0 ) outside of the cells. 32) These results suggest the possibility that aa 3 -type cytochrome c oxidase, which plays an important role as a terminal oxidase in the iron oxidation enzyme system of A. ferrooxidans, has biological activity other than intrinsic terminal oxidase activity, such as activity detoxifying toxic mercuric ions.…”

“…We recently found that A. ferrooxidans SUG 2-2 has not only NADPH-dependent mercury reductase activity but also Fe 2þ -dependent mercury reductase y To whom correspondence should be addressed. Tel/Fax: +81-86-251-8306; E-mail: sugio@cc.okayama-u.ac.jp activity in cells, 31) and, that cytochrome c oxidase purified from strain SUG 2-2 volatilizes mercury in the presence of Fe 2þ . 32) Interestingly, iron oxidase activity, cytochrome c oxidase activity, and Fe 2þ -dependent mercury volatilization activity increased markedly in MON-1 cells as compared with those in a parent strain, SUG 2-2.…”