ENERGY TRANSFORMATION 



401 



viously treating the water with KM11O4. The ratio between the sulfur 

 oxidized and carbon assimilated from CO2 of the atmosphere (S:C) 

 was found to be about 32. With thiosulfate as a source of energy the 

 ratio was found to be about 64. The apparatus used for carbon de- 

 termination is given in figure 16. 



About six and two-thirds per cent of the heat liberated in the oxida- 

 tion of elementary sulfur is utilized for the chemosynthetic assimilation 

 of carbon. 35 However, when conditions are unfavorable for the de- 

 velopment of the organism, the sulfur-carbon ratio may increase. For 

 example, the presence of nitrates in the medium, which exerts a toxic 

 effect upon the respiration of the organism, resulted in a wider sulfur- 



TABLE 26 

 Influence of carbon source upon the growth and sulfur oxidation of Thiobacillus 



thiooxidans 



* Titre = cubic centimeter of 0.1N NaOH necessary to neutralize 10 cc. of 

 medium, with phenolphthalein as indicator. 



carbon ratio. The sulfates were found to have no effect on the respira- 

 tion of the sulfur oxidizing bacteria, except in very high concentrations. 

 Nitrates are very toxic, especially in concentrations above 0.2 molar. 

 Phosphates proved to be more toxic than sulfates, but less toxic than 

 nitrates. As stated above, glucose was not found to be toxic, but 

 peptone became toxic in concentrations of 0.05 per cent. The concen- 

 tration of sulfur in the medium did not exert any important influence 

 on sulfur oxidation; an increase in the quantity of sulfur led to an 

 increase in oxidation. As to the influence of sulfuric acid or the prod- 



35 Waksman, S. A., and Starkey, R. L. On the growth and respiration of sulfur 

 oxidizing bacteria. Jour. Gen. Physiol., 5: 285-310. 1923. 



