EFFICIENCY OF CHEMAUTOTROPHIC BACTERIA 



119 



oxidized by oxygen, while carbon dioxide is reduced independently by 

 water (c/. page 235). The efficiency has been determined for several 

 species, and the results have been discussed, among others, by Baas- 

 Becking and Parks (1927), Burk (1931), and Stern (1933). Many 

 measurements have not been very reHable, so that most of the figures 

 collected in table 5. VII should be considered as preliminary. 



Table 5.VII 

 Efficiency of Autotrophic Bacteria 



" AF of {CH2O) synthesis, for p(C02) = 3 X 10-« atm. and p(02) = 0.2 atm., is 118 kcal (c/. Table. 

 3 V) 



' Calculated for [NH4+] = 5 X 10"= moleA- and [H+] = lO-s mole/1. 



' Calculated for [NO2-] = 3 X lO"' mole/I. , . • 



"* We put these values in parentheses because we believe (c/. page 226) that they apply to primary 

 carbon dioxide fixation rather than to carbon dioxide reduction. The same may be true of the low ratios 

 AO2/ACO2 observed by Sohngen for methane bacteria. i>t o /a 



'Baas-Becking and Parks calculated 11%. They thought that Lieske's yields refer to 1 g. Na2S203 

 instead of 1 g. Na2S!03-5 H2O. 



/ 42% is maximum, and 26% the average. ... o-i, 



The larger values were calculated by Baas-Becking and Parks from the gasometnc data of bohngen, 

 while the smaller were obtained from the permanganate titration of organic matter. Cf. footnote "■ above. 



For the majority of organisms in table 5. VII, the "energy yields" 

 are of the order of 5-6%, and the "free energy yields" of the order of 

 6-8%. The difference is due to the fact that the free energies of oxi- 

 dations leading to the formation of electrolytes often are considerably less 

 negative than the corresponding total energies. 



Although low, the efficiencies in table 5. VI I are similar to the best 

 efficiencies of the utilization of light energy by green plants under natural 

 conditions. Thus, if chemautotrophic organisms did not succeed in 

 spreading over the whole surface of the earth, as did the green plants, 

 it was not for lack of efficiency, but merely because chemical energy is 

 available only in a few nonequilibrated spots — sulfur springs, coal mines, 

 iron carbonate waters, marsh gases, etc., while sunlight flows abundantly 

 everywhere. 



