138 



ANAEROBICALLY ADAPTED ALGAE 



CHAP. 6 



site of the hydrogen fermentation is in the chloroplasts (while acid 

 fermentation may occur everywhere in the cell). 



The nonvolatile acids, produced by the autofermentation of algae, 

 contained only a few per cent of lactic acid, while in presence of glucose, 

 this percentage reached 50%. (In some colorless heterotrophic organ- 

 isms, the fermentation of glucose produces up to 95% lactic acid.) 



The mechanism of the hydrogen evolution and absorption by algae 

 which contain an active hydrogenase, can be represented by equations 

 (6.2) and (6.3), (or 6.6a,b): the hydrogen is transferred from the atmos- 

 phere, through the reversible systems, Eh-H2Eh and Ah-H2Ah (and 

 probably through specific oxidoreductases), to a cellular oxidant, R; or 



3 4 



Time, hours 



6 



Fig. 10. — Increase in fermentation and hydrogen production in Scenedesmus by 

 glucose (after Gaffron 1942i). 



Final sugar concentration, 0.06%. Curve 1: carbon dioxide with acid. Curve 

 la: carbon dioxide and acid after addition of glucose. Curve 2: hydrogen. Curve 2a: 

 hydrogen after addition of glucose. 



from a cellular reductant R'H2, through a similar catalytic system, back 

 into the atmosphere. The direction of the process should depend on the 

 oxidation-reduction potentials of the cellular reserve substances R and 

 R', on their concentrations, and on the partial pressure of hydrogen. 



(Ill) and (IV). Oxyhydrogen Reaction and the Reduction of Carbon 

 Dioxide in the Dark (Algae as Chemautotrophic Bacteria). — As men- 

 tioned on page 132, small quantities of oxygen prevent anaerobic adapta- 

 tion, but after adaptation, they are tolerated, without causing a return 

 to normal photosynthesis, because they are used up by the oxyhydrogen 

 reaction. If a few millimeters of oxygen are added to an adapted 

 Scenedesmus culture in a hydrogen atmosphere, in the dark, the algae 



