Effect of various ions, pH, and osmotic pressure on oxidation of elemental sulfur by Thiobacillus thiooxidans

Abstract

The oxidation of elemental sulfur by Thiobacillus thiooxidans was studied at pH 2.3, 4.5, and 7.0 in the presence of different concentrations of various anions (sulfate, phosphate, chloride, nitrate, and fluoride) and cations (potassium, sodium, lithium, rubidium, and cesium). The results agree with the expected response of this acidophilic bacterium to charge neutralization of colloids by ions, pH-dependent membrane permeability of ions, and osmotic pressure.

FIG. 1

Effect of potassium or sodium sulfate and phosphate concentrations on the oxidation of sulfur at pH 2.3, 4.5, and 7.0 and effect of DNP. The rate of O₂ consumption was determined with sulfur dissolved in DMSO. The DNP concentration, when DNP was present, was 6.25 μM. Different batches of cells were used for the potassium and sodium sulfate experiments, while the phosphate experiments were carried out with the same batch of cells.

FIG. 2

Effect of potassium or sodium phosphate concentrations on the oxidation of sulfur at pH 2.3, 4.5, and 7.0.

FIG. 3

Effect of potassium, sodium, or lithium chloride (left); potassium or sodium nitrate (middle); and potassium, sodium, or lithium fluoride (right) concentrations on the oxidation of sulfur at pH 2.3.

FIG. 4

Effect of 500 mM sucrose with and without preincubation. Conditions were as described in the text, except that the activity in 500 mM sucrose was determined with (dashed line) and without (solid line) 2 h of preincubation of cells in sucrose before the addition of sulfur to start the reaction. O₂ consumption tracings in the absence of 500 mM sucrose (in water and in 50 mM K₂SO₄) are also shown for the oxidation of sulfur at pH 2.3.