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

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

“…The reaction mixture (2.5 ml) contained resting cells of A. ferrooxidans strain MON-1 (0.005 mg), 0.1 Malanine-SO 4 2À buffer (2.0 ml), and 0.2 M TMPD (100 ml). The reaction was initiated by the addition of resting cells, and was carried out at 30 C for 5 min.…”

“…The activity of cytochrome c oxidase was measured as the decrease in absorbance at 550 nm due to the oxidation of reduced mammalian cytochrome c (Nakalai Tesque, Kyoto, Japan, from horse heart) at 30 C using a Shimadzu UV-1700 spectrophotometer. The reaction mixture contained purified cytochrome c oxidase, reduced cytochrome c (32 nmol), and 0.1 M acetate buffer, pH 4.2.…”

“…The reaction mixture without resting cells was added to an anaerobic cuvette, degassed, and bubbled with nitrogen gas for 5 min. After the reactions were preincubated for 5 min at 30 C, the reaction was initiated by the addition of resting cells, and was carried out under anaerobic conditions at 30 C for 3 h. Each of the reaction flasks contained a reaction mixture (10 ml) plus 0.4 ml of a KMnO 4 solution. The 100 ml of KMnO 4 solution used was composed of KMnO 4 (0.6 g), concentrated H 2 SO 4 (5 ml), and deionized water (95 ml).…”

“…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. 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,[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.…”