THE HYDROGEN BACTERIA 



117 



and most efficient carbon dioxide-assimilating biological systems known, 

 a few words must be said here on his results. 



Bacillus picnoticus thrives best in inorganic media at pH 6.8 to 8.7; 

 the decline in its activity in alkaline solutions seems to be caused by the 

 precipitation of ferric hydroxide. (It requires a minimum concentration 

 of ferrous iron > 10"^ mole per 1.) It is poisoned by cyanide (5 X 10"^ 

 mole/1.) as well as by urethans (50% reduction in hydrogen consumption 

 by 1.2 moles/1, methylurethan, 2 X 10"^ ethylurethan, 1 X 10"^ propyl- 

 urethan, 5 X 10"^ isobutylurethan, and 1 X 10"* phenylurethan ; com- 

 pare table 12. VIII). 



While some hydrogen bacteria can use nitrate as oxidant (in absence 

 of oxygen), no such substitution is possible with B. picnoticus. Its rate 

 of consumption of hydrogen is independent of the partial pressure of 

 oxygen (1.5 to 72%) as well as hydrogen. It can operate in "electrolytic 

 gas" (I H2 + ^02), and in nitrogen containing mere traces of oxygen 

 and hydrogen (these traces being completely removed by the activity of 

 the bacteria). The concentration of carbon dioxide is also without 

 specific effect except by its indirect influence on acidity. 



The rate of hydrogen absorption increases rapidly with temperature 

 (Qio = 3.5 between 20° and 32.5" C). Since the combustion is coupled 

 with the reduction of carbon dioxide, the net ratio AH2/AO2 is larger 

 than 2 (Table 5. VI), the excess hydrogen consumption reaching 40% 



Table 5.VI 

 Gas Exchange of Bacillus Picnoticus (after Ruhland) 



Average : 



2.56 



0.52 



under the most favorable conditions. The consumption of carbon 

 dioxide, - ACO2, is in exact stoichiometric relationship with the excess 

 consumption of hydrogen, - (zlHg - 2AO2). This " photosynthetic 



