118 PHOTO- AND CHEMOSYNTHESIS OF BACTERIA CHAP. 5 



quotient" is equal to 0.5, indicating the formation of a carbohydrate as 

 the first product of chemosynthesis. 



Some heterotrophic bacteria (e. g., Acetobader peroxidans, cf. Wieland 

 and Pistor 1936, 1938) also catalyze the " oxyhy drogen " reaction (5.30) 

 but apparently without profiting from its energy for organic synthesis. 



(e) The Carbon Bacteria 

 The Carbon Monoxide Oxidizers (Bacillus oligocarbophilus) (Beijer- 

 inck and van Delden 1903). 



The reaction which these bacteria catalyze is: 



(5.32) O2 + 2 CO > 2 CO2 + 136 kcal 



which produces no less energy than does the oxidation of hydrogen. 



Methane Oxidizers. — (Bacillus metanicus), (Sohngen 1906, Miinz 

 1915). Although methane is usually considered an "organic" carbon 

 compound, we inlcude the methane-burning bacteria in the list of chemo- 

 autotrophic organisms because there is no doubt that methane serves 

 exclusively as a source of energy and as a hydrogen donor, and not as an 

 organic nutrient. 



The combustion of methane liberates less energy than that of 

 hydrogen : 



(5.32) 02 + ^ CH4 > h CO2 + H2O + 106 kcal 



but considerably more than the oxidation of ammonia or ferrous iron. 



The Benzene and Toluene Oxidizers. — These bacteria, discovered by 

 Tausson (1929), seem to be similar to Sohngen's methane bacteria in 

 that they too use the energy of oxidation of a hydrocarbon for the 

 synthesis of organic matter from carbon dioxide. 



Carbon Oxidizers. — We mention lastly the carbon bacteria of Potter 

 (1908) which can live autotrophically by oxidizing solid carbon to carbon 

 dioxide : 



(5.33) C + O2 > CO2 + 94 kcal 



2. Efficiency of Chemauto trophic Bacteria 



The efficiency of the autotrophic bacteria can be expressed in three 

 different ways: by the molecular ratio (AO2 consumed by oxidation 

 divided by ACO2 reduced to organic matter; the latter quantity being 

 determined either directly, or from the amount of synthesized organic 

 material) ; by the ratio of energies (AHr accumulated in synthesis divided 

 by AHo liberated by oxidation); and by the corresponding ratio of the 

 free energies (— AFr accumulated to AFo dissipated). Only the first 

 ratio is derived directly from experiments. The calculation of the last 

 two is based on the fiction that all of the oxidation substrate is completely 



