title: Volatilization of mercury by an iron oxidation enzyme system in a highly mercury-resistant Acidithiobacillus ferrooxidans strain MON-1.
abstract: A highly mercury-resistant strain Acidithiobacillus ferrooxidans MON-1, was isolated from a culture of a moderately mercury-resistant strain, A. ferrooxidans SUG 2-2 (previously described as Thiobacillus ferrooxidans SUG 2-2), by successive cultivation and isolation of the latter strain in a Fe2+ medium with increased amounts of Hg2+ from 6 microM to 20 microM. The original stain SUG 2-2 grew in a Fe2+ medium containing 6 microM Hg2+ with a lag time of 22 days, but could not grow in a Fe2+ medium containing 10 microM Hg2+. In contrast, strain MON-1 could grow in a Fe2+ medium containing 20 microM Hg2+ with a lag time of 2 days and the ability of strain MON-1 to grow rapidly in a Fe2+ medium containing 20 microM Hg2+ was maintained stably after the strain was cultured many times in a Fe2+ medium without Hg2+. A similar level of NADPH-dependent mercury reductase activity was observed in cell extracts from strains SUG 2-2 and MON-1. By contrast, the amounts of mercury volatilized for 3 h from the reaction mixture containing 7 microM Hg2+ using a Fe(2+)-dependent mercury volatilization enzyme system were 5.6 nmol for SUG 2-2 and 67.5 nmol for MON-1, respectively, indicating that a marked increase of Fe(2+)-dependent mercury volatilization activity conferred on strain MON-1 the ability to grow rapidly in a Fe2+ medium containing 20 microM Hg2+. Iron oxidizing activities, 2,3,5,6-tetramethyl-p-phenylenediamine (TMPD) oxidizing activities and cytochrome c oxidase activities of strains SUG 2-2 and MON-1 were 26.3 and 41.9 microl O2 uptake/mg/min, 15.6 and 25.0 microl O2 uptake/mg/min, and 2.1 and 6.1 mU/mg, respectively. These results indicate that among components of the iron oxidation enzyme system, especially cytochrome c oxidase activity, increased by the acquisition of further mercury resistance in strain MON-1. Mercury volatilized by the Fe(2+)-dependent mercury volatilization enzyme system of strain MON-1 was strongly inhibited by 1.0 mM sodium cyanide, but was not by 50 nM rotenone, 5 microM 2-n-heptyl-4-hydroxy-quinoline-N-oxide (HQNO), 0.5 microM antimycin A, or 0.5 microM myxothiazol, indicating that cytochrome c oxidase plays a crucial role in mercury volatilization of strain MON-1 in the presence of Fe2+.
authors.affiliation: Graduate School of Natural Science and Technology, Science and Technology for Energy Conversion, Okayama University, Japan. sugio@cc.okayama-u.ac.jp
authors.forename: Tsuyoshi
authors.initials: T
authors.lastname: Sugio
authors.forename: Mitsuko
authors.initials: M
authors.lastname: Fujii
authors.forename: Fumiaki
authors.initials: F
authors.lastname: Takeuchi
authors.forename: Atsunori
authors.initials: A
authors.lastname: Negishi
authors.forename: Terunobu
authors.initials: T
authors.lastname: Maeda
authors.forename: Kazuo
authors.initials: K
authors.lastname: Kamimura
mesh_terms: D002701:Chloramphenicol / Q000494:pharmacology; D003470:Culture Media; D024881:Drug Resistance, Bacterial; D004579:Electron Transport / Q000187:drug effects; D003576:Electron Transport Complex IV / Q000378:metabolism; D007501:Iron / Q000378:metabolism*; D008628:Mercury / Q000378:metabolism* / Q000494:pharmacology*; D009249:NADP / Q000378:metabolism; D010084:Oxidation-Reduction; D013855:Thiobacillus / Q000145:classification / Q000187:drug effects* / Q000201:enzymology* / Q000302:isolation & purification; D014835:Volatilization
chemical_list: D003470:Culture Media; D009249:NADP; D002701:Chloramphenicol; D007501:Iron; D003576:Electron Transport Complex IV; D008628:Mercury