Isolation and some properties of Thiobacillus ferrooxidans strains with differing levels of mercury resistance from natural environments

Citation
F. Takeuchi et al., Isolation and some properties of Thiobacillus ferrooxidans strains with differing levels of mercury resistance from natural environments, J BIOSCI BI, 88(4), 1999, pp. 387-392
Citations number
17
Categorie Soggetti
Biotecnology & Applied Microbiology",Microbiology
Journal title
JOURNAL OF BIOSCIENCE AND BIOENGINEERING
ISSN journal
13891723 → ACNP
Volume
88
Issue
4
Year of publication
1999
Pages
387 - 392
Database
ISI
SICI code
1389-1723(199910)88:4<387:IASPOT>2.0.ZU;2-B
Abstract
Fifty iron-oxidizing bacteria isolated from natural environments were scree ned for resistance to mercuric ions (Hg2+). Thiobacillus ferrooxidans Funis 2-1, the strain found to show the greatest resistance to Hg2+ among the fi fty isolates, gave a cell yield of 7.0 x 10(7) cells/ml after 8 d cultivati on in an Fe2+-medium (pH 2.5) containing 0.7 mu M Hg2+. Funis 2-1 volatiliz ed 80% of the total mercury added to the medium over 8 d of cultivation. T. ferrooxidans AP19-3, more sensitive to Hg2+ than Funis 2-1, could not grow in an Fe2+-medium (pH 2.5) containing 0.7 mu M Hg2+ even over a 28 d culti vation period. When resting cells of strains Funis 2-1 and AP19-3 were incu bated for 3 h in a salt solution containing 0.7 mu M Hg2+ (pH 3.0), 14.3% a nd 7.9% of the total mercury added to the reaction mixtures respectively, w ere volatilized. The activity of the mercuric reductase from Funis 2-1 was only 2.8 times higher than that of the enzyme from AP19-3. Since the marked ly higher mercury resistance of Funis 2-1 compared with that of AP19-3 cann ot be explained only by the level of the mercuric reductase activity, the l evels of mercury resistance of iron oxidase and cytochrome c oxidase were s tudied. The 1 mu M mercuric ions inhibited the 35% of iron-oxidizing activi ty from AP19-3. In contrast, the same concentration of Hg2+ did not inhibit the activity of iron oxidase from Funis 2-1. In the case of the cytochrome c oxidases purified from both strains, the 0.2 mu M Hg2+ inhibited approxi mately 40% of cytochrome c oxidizing activity from AP19-3, on the contrary, the activity of the enzyme from Funis 2-1 was activated 1.8- and 1.2-fold, respectively, in the presence of 0.08 and 0.2 mu M Hg2+. Since cytochrome c oxidase is one of the most important components of the iron-oxidizing sys tem, these results indicate that both the existence of cytochrome c oxidase resistant to Hg2+ as well as that of mercuric reductase in the cells is re sponsible for the more rapid growth of Funis 2-1 than that of in an Fe2+-me dium containing 0.7 mu M Hg2+.