Since the activities of sulfur bacteria are known to be responsible for many of the characteristics of acid-mine wastes, investigations were aimed at elucidating the physiology and metabolism of these bacteria as this approach appears to be the key to the development of control measures. The investigations show that thiobacilli are the most prolific producers of sulfates from the oxidation of sulfur compounds. Under laboratory conditions, an average population of thiobacilli was found. Assuming that the rate of sulfur transformation in natural environments having enrichment of these organisms is approximately 10% of the transformations observed under laboratory conditions, then the thiobacilli could produce as much as 100 to 400 moles of sulfates in one hour in the upper one foot of water in an area of one acre. However concentrations as low as 0.000001 to 10 to the minus seventh power of chloro or bromo-substituted phenols were effective in the complete inhibition of the energy metabolism of thiobacilli.