Cytochrome c Oxidase Purified from a Mercury-Resistant Strain of Acidithiobacillus ferrooxidans Volatilizes Mercury.

Abstract

We suggested in our previous study that the plasma membrane cytochrome c oxidase of the mercury-resistant iron-oxidizing bacterial strain Acidithiobacillus ferrooxidans, SUG 202, is involved in Fe2+-dependent mercury volatilization. To study the involvement of A. ferrooxidans cytochrome c oxidase in mercury reduction, the cytochrome c oxidase was extracted from mercury-resistant and mercury-sensitive strains and purified. The Fe2+-dependent mercury volatilization activities of the oxidases from these strains were compared. The cytochrome c oxidase from strain SUG 2-2 volatilized 39% of the total Hg2+ (7 nmol) that had been added to a 10-ml reaction mixture (pH 3.8) in the presence of 10 micromol of Fe2+ after a 7-d incubation period at 30 degrees C. In contrast, the enzyme purified from the mercury-sensitive strain AP19-3 volatilized 3.5% of the total mercury under the same conditions. The boiled SUG 2-2 oxidase did not exhibit activity to volatilize mercury. Fe2+ reduced the oxidase from SUG 2-2 and Hg2+ oxidized the reduced enzyme. The purified SUG 2-2 oxidase is composed of three protein subunits with apparent molecular weights of 56,000 Da (alpha), 24,000 Da (beta), and 19,000 Da (gamma). The amount of mercury bound to the purified SUG 2-2 oxidase was 6.2 microg/mg protein and those bound to alpha-, beta- and gamma-subunits of the cytochrome c oxidase were 3.5, 2.6 and 0.7 microg/mg protein, respectively.

Growth in sulfidic mineral environments: metal resistance mechanisms in acidophilic micro-organisms

“…The reduction is thought to be catalysed by the cytochrome-c oxidase . There is interest in making use of this strain's Hg(II)-reducing capabilities and it has been studied for use in bioremediation of mercury-polluted acidic sites (Takeuchi et al, 2001). The difference between mercury-sensitive and -resistant strains of At.…”

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

“…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. 2,3,5,6-tetramethyl-pphenylenedimine (TMPD) is an artificial substrate used in the measurement of cytochrome c oxidase activity.…”

“…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. 30) However, the levels of NADPHdependent mercuric reductase activity in the cytosol were nearly the same in both of the mercury-resistant strains.…”

“…Although the same amounts of ferrous iron were oxidized when strains MON-1 and ATCC 23270 gave maximum cell yields, the growth yield of strain MON-1 was It is well known that aa 3 type cytochrome c oxidase is one of the most important components of the iron oxidation enzyme system in A. ferrooxidans. 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.…”

“…These results strongly suggest that the enhancement of mercury resistance in A. ferrooxidans MON-1 is due to the increment of iron oxidase activity, probably to the increment of cytochrome c oxidase, which has an activity reducing Hg 2þ with ferrous sulfate as an electron donor. 32) Although we have found that cytochrome c oxidase purified from SUG 2-2 reduces Hg 2þ with ferrous iron as an electron donor, to prove directly the involvement of cytochrome c oxidase in Hg 2þ reduction, it is absolutely necessary to clarify Hg 2þ reduction with not only Fe 2þ but also with reduced cytochrome c as an electron donor in the presence of cytochrome c oxidase, because reduced cytochrome c is a known substrate specific for cytochrome c oxidase.…”