ENERGY TRANSFORMATION 403 



2. Those which do not require ferrous bicarbonate for their life processes 

 but which deposit ferric hydroxide when either inorganic or organic iron salts 

 are present (facultative autotrophic). 



3. Those which attack organic iron salts, using the organic acid radical as a 

 nutrient and precipitating ferric hydroxide or basic ferric salts which are gradu- 

 ally changed to ferric hydroxide. Inorganic iron salts, however, are not utilized 

 as sources of energy and this group is heterotrophic. 



Energy utilization from the oxidation of hydrogen. The oxidation of 

 hydrogen by bacteria is accompanied by the liberation of large quanti- 

 ties of heat, according to the following reaction: 



H 2 + KOj) = H 2 -f- 6S.4 Cal. 



Thus 1 gram of hydrogen gives more than eight times as much heat of 

 combustion (34.2 Cal.) as 1 gram of starch (4.1 Cal.). Some of the 

 hydrogen bacteria {Hydrogenomonas pantotropha) can grow on purely 

 inorganic media, utilizing the energy obtained from the oxidation of 

 hydrogen for the assimilation of carbon chemosynthetically from the 

 C0 2 of the atmosphere. 38 Kaserer suggested that the mechanism of 

 hydrogen transformation will depend on the nature of the organism. 



Hydrog. pantotropha changes the hydrogen and carbon dioxide directly 

 into the first substance necessary for the synthesis of organic matter, 

 namely to formaldehyde. 



H 2 CO, + 2 H 2 = C H 2 + 2 H 2 0; CH 2 + 2 = H 2 C0 3 



The oxidation of hydrogen is thus found to lead to two processes, 

 assimilation of carbon dioxide and oxidation of the hydrogen. For 

 every volume of C0 2 assimilated, two volumes of hydrogen gas are 

 oxidized. For every two volumes of hydrogen oxidized one volume 

 of oxygen disappears. The formation of formaldehyde as an inter- 

 mediary product was not confirmed by Lebedeff . The bacteria (Hydrog. 

 vitrea and Hydrog. flava) isolated by Niklewski 39 also grew in an inorganic 

 solution with an atmosphere of H 2 , O2, and C0 2 . Organic compounds 

 were formed from the hydrogen and carbon dioxide; those were then 

 oxidized to carbon dioxide and water during respiration. The auto- 

 trophic nature of the process has been definitely established by Lebe- 



88 Kaserer, 1906 (p. 97). See Klein and Svolba, Ztschr. Bot. 19: 65. 1926. 



39 Niklewski, 1910 (p. 98). 



<0 Lebedeff, A. F. tiber die Assimilation des Kohlenstoffes bei wasserstoff- 

 oxydierenden Bakterien. Ber. deut. bot. Geaell., 27: 598-602. 1909. Nabokich 

 and Lebedeff, 1907 (p. 98). 



