Effect of Phosphate Ion and 2,4-dinitropehenol on the Activity of Intact Cells of Thiobacillus Ferrooxidans.

Beck, Jay V. (Brigham Young University, Provo, Utah), and Fred M. Shafia. Effect of phosphate ion and 2,4-dinitrophenol on the activity of cell suspensions of Thiobacillus ferrooxidans. J. Bacteriol. 88:850-857. 1964.-The rate of oxidation of ferrous salts or elemental sulfur by aged cell suspensions, phosphate-depleted cells, or 2,4-dinitrophenol (DNP)-treated cells of Thiobacillus ferrooxidans was increased by addition of orthophosphate salts. The effect was found to be transitory, with the rate gradually approaching that observed prior to phosphate ion addition. The total increased oxygen uptake was observed to be roughly proportional to the amount of phosphate salt added. The efficiency of CO(2) fixation accompanying oxidation of ferrous salts was found to be about 1.7 mumoles of CO(2) fixed per 100 mumoles of O(2) absorbed, in contrast to a value of about 8.0 mumoles of CO(2) fixed per 100 mumoles of O(2) uptake during sulfur oxidation. The rate of oxidation did not affect the CO(2) fixation efficiency. Whereas addition of phosphate salts to aged or phosphate-depleted cells increased slightly the already high efficiency of CO(2) fixation, it did not affect the complete inhibition of CO(2) fixation observed in the presence of 10(-5)m DNP. The results indicate that the phosphate ion is essential for oxidation of the ferrous ion, and that dinitrophenol and other so-called upcoupling agents interfere with phosphate metabolism. The latter may be a result of action at the site of assimilation of the ferrous ion or it may be an effect on the electron-transport system. In any event, it seems obvious that the phosphate ion is converted into a nonactive form in the presence of dinitrophenol-treated cells, because additional quantities of orthophosphate salts cause an immediate, marked restoration of oxidative activity.