Inhibition of Sulfur Oxidizing Activity by Nickel Ion inThiobacillus thiooxidansNB1–3 Isolated from the Corroded Concrete

Abstract

It is of great importance to find ways to protect concrete from corrosion, to maintain the concrete structure for a long time. A sulfur-oxidizing bacterium, Thiobacillus thiooxidans, has been known to play a crucial role in concrete corrosion and the concrete supplemented with nickel was resistant to corrosion. To obtain biological bases of this Ni protection, the effects of Ni on sulfur dioxygenase and sulfite oxidase of T. thiooxidans NB1–3 isolated from corroded concrete were studied. Nickel sulfate strongly inhibited a sulfur dioxygenase that catalyzes the oxidation of elemental sulfur to shlfite and a sulfite oxidase that catalyzes oxidation of sulfite to sulfate. Nickel sulfate, antimycin A, 2-n-heptyl-4-hydroxyquinoline-N-oxide, and myxothiazol inhibited both sulfite oxidase and ubiquinol oxidase. Reduced mammalian cytochrome c was not oxidized by a cell extract of strain NB1–3. The b and a-type cytochromes in the plasma membrane was reduced by sulfite and ubiquiuol-2 and these reductions were inhibited by NiSO4. The amounts of Ni in the plasma membrane with or without 0.1 mm nickel treatment were 32.6 and 2.8nmol/mg protein, respectively. These results indicate that nickel binds to the plasma membrane and inhibits sulfur dioxygenase and sulfite oxidase, and as a result, inhibits cell growth.