ENERGY TRANSFORMATION 421 



action of two organisms, as in the case of cellulose oxidation and de- 

 nitrification. 76 Trautwein 77 pointed out that Thiob. denitrificans, 

 which oxidizes thiosulfate aerobically, can carry on this process in the 

 absence of atmospheric oxygen but in the presence of nitrates. When 

 tartaric acid is oxidized by atmospheric oxygen or by reduction of 

 nitrates, nearly equal amounts of energy are liberated, since the reduc- 

 tion of nitrates to atmospheric nitrogen does not consume a large 

 amount of energy. 



C 4 H 6 6 + 2§ (0 2 ) = 4 C0 2 + 3 H 2 + 282 Cal. 

 Tartaric acid 



C 4 H 6 6 + 2 HN0 3 = 4 C0 2 + 4 H 2 + N 2 + 253.4 Cal. 



Attention should also be called to the reduction of nitrate in the as- 

 similation of nitrate by the chlorophyll-bearing algae 73 and to the 

 role of nitrate as hydrogen acceptor in the growth of certain anaerobic 

 bacteria. The first is carried through the following series of reactions: 



N07+ H 2 + 2 H+ = NHt + 2 2 - 68 Cal. 

 2 2 + 2 C = 2 C0 2 + 230 Cal. 



or 



N07 + H 2 -j-2H+ + 2C = NHf + 2 C0 2 + 162 Cal. of free energy 



Out of a total of 230 Cal. liberated, only 68 Cal. or about 30 per cent 

 is utilized for the reduction of the nitrate. The question of nitrate 

 reduction by bacteria will be discussed in detail elsewhere (p. 545). 79 

 The reduction of sulfate to sulfide requires a large expenditure of 

 energy and accounts for the distinct difference in energy gain when 

 oxidation takes place by means of atmospheric oxygen or when the 

 oxygen is derived from the reduction of sulfates. 



H 2 S0 4 = H 2 S + 2 2 - 135 Cal. 



2 C 3 H 6 3 + 6 2 = 6 CO, + 6 H 2 + 659 Cal. 

 lactic acid 



2 C 3 H 6 3 + 3 H 2 S0 4 = 6 C0 2 + 6 H 2 + 3 H 2 S + 254 Cal. 



76 Groenewege, 1920 (p. 200). 



77 Trautwein, 1921 (p. 87). 



78 Warburg, O., and Negelein, E. Uber den Energieumsatz bei der^Kohlen- 

 saureassimilation. Ztschr. physik. Chem., 102: 235-266. 1922. 



79 Jensen, Orla. Die Hauptlinien des natiirlichen Bakteriensystems. Centrbl. 

 Bakt. II, 22: 97-98, 305-346. 1909. 



