406 PRINCIPLES OF SOIL MICROBIOLOGY 



gen. 41 On the acid side, growth diminishes due to the disappearance 

 of HCO,3~ (in favor of CO2) and to the direct action of the hydrogen-ion 

 on the hydrogen oxidation. On the alkaline side, growth diminishes 

 due to an increasing diminution of the iron. Organic carbon sources 

 exert a certain protective action upon the oxidation of the hydrogen 

 due to the production of organic acids and, therefore, a reaction un- 

 favorable to the bacteria. Organic substances, which do not result 

 in formation of acid, as well as small amounts of sugar, tend to slow 

 down the oxidation of hydrogen at first, but then accelerate it. The 

 reaction is carried on to completion, so long as there are any traces of 

 H 2 and 2 in the atmosphere. Different C0 2 pressures influence 

 growth by influencing the reaction. The hydrogen-oxygen (elemental) 

 ratio is usually greater than two to one, reaching 2.78 because of the 

 formation of free oxygen in the reduction of C0 2 . The most efficient 

 utilization of the energy of the reaction for chemosynthetic purposes 

 is at a neutral reaction when 1 cc. C0 2 is assimilated for 8 cc. H 2 oxi- 



.„,.... „ C0 2 assimilated .. , 



dized. Ihe utilization quotient Qn = — lies between 



H« oxidized 



0.01 and 0.148. As much as 20 per cent of the energy liberated may 



be used for the chemosynthetic assimilation of C0 2 . Partial pressure 



of H 2 has no influence on the energy utilization and C0 2 assimilation. 



Nitrate is reduced to nitrite (not to atmospheric nitrogen), but the 



oxygen cannot be used for the anaerobic oxidation of hydrogen. 



Narcotics (urethane, HCN) exert an injurious effect upon oxidation. 



Energy utilization from the oxidation of simple carbon compounds. 



Methane is oxidized by certain bacteria which use the energy thus 



obtained for the chemosynthetic utilization of C0 2 . 



CH 4 -f 2 2 = C0 2 + 2 H 2 + 218 Cal. 



This process is carried out, under autotrophic conditions, by Metha- 

 nomonas methanica. 42 Mlinz 43 found these bacteria developing 

 readily in an atmosphere rich in methane with an optimum concen- 

 tration of oxygen at 2 per cent. Nitrogen is utilized in inorganic 

 and organic forms. The organism is facultative autotrophic, being 



41 Ruhland, W. Aktivierung von Wasserstoff und Kohlensaureassimilation 

 durch Bakterien. Ber. deut. Bot. Gesell., 40: 180-184. 1920-1922; also Ruhland, 

 1924 (p. 101). 



42 Sohngen, 1906 (p. 96). 



43 Miinz, E. Zur Physiologie der Methanbakterien. Diss. Halle. 1915. 



