Nickel inhibition of the growth of a sulfur-oxidizing bacterium isolated from corroded concrete

A sulfur-oxidizing bacterium strain NB1-3 isolated from corroded concrete was a Gram negative, non-spore-forming, and rod-shaped bacterium (0.5-1.0 x 1.5-2.0 mu m) with a polar flagellum. Strain NB1-3 had its optimum temperature and pH for growth at 30 degrees C and 3.0-1.0, respectively. Strain NB1-3 had enzyme activities that oxidized elemental sulfur, thiosulfate, tetrathionate, and sulfide and the activity to incorporate (CO2)-C-14 into the cells. The mean G+C content of the DNA was 52.9 mol%. These results indicate that strain NB1-3 is Thiobacillus thiooxidans. Since nickel has been known to protect concrete from corrosion, the effect of Ni on the growth of strain NB1-3 was studied. The cell growth on tiosulfate-, elemental sulfur-, or tetrathionate-medium was completely inhibited by 0.1% metal nickel or 5 mM NiSO4. Both cellular activities of elemental sulfur oxidation and CO2 incorporation were strongly inhibited by 5 mM NiSO4. The amounts of Ni in cells with or without nickel treatment were 1.7 and 160.0 nmol/mg protein, respectively. These results indicate that nickel binds to strain NB1-3 cells and inhibits enzymes involved in sulfur oxidation of this bacterium, and as a result, inhibits cell growth.