594 



YOSHIHARU ODA 



the ability to evolve or utilize H2 is not a restricted metabolic potentiality but 

 rather that this type of activity is found in a large number of organisms of widely 

 different physiological types. This fact does not only suggest that H2 meta- 

 bolism represents a fundamental aspect of microbial physiology, but that the 

 deUberate study of it forms the basis for an approach to the comparative bio- 

 chemistry of electron pathways. 



In this report, the author will discuss particularly the significance of mole- 

 cular hydrogen metabolism in the transitionary stage from anaerobiosis to 

 aerobiosis. 



STAGE OF ANAEROBIOSIS 



The abiUty to evolve or utilize H2 — the reaction of hydrogenase system — 

 appears to be mainly restricted to strict and facultative anaerobic micro-organisms. 

 In the facultative anaerobes hydrogenase system occurs only in anaerobic culture 

 conditions [3, 4]. Also in the photosynthetic micro-organisms such as green algae 

 Scenedesmiis [5], and Rhodospirillum rubrum [6], photochemical Hj production 

 occurs only after an extended dark anaerobic adapatation period. From these 

 facts, it may be inferred that the ability to evolve or utilize H2 has developed in 

 the stage of anaerobic heterotrophy in which primitive living beings hved 

 depending on the primary organic substances, produced in the regions of ancient 

 sea physico-chemically, rather than by living beings. It is known that in this 

 ancient stage, O2 gas was not present in the atmosphere. Accordingly these 

 primitive living beings could bring about energy-yielding reactions by anaerobic 

 fermentations, and utilize the energy hberated from these processes for life 

 processes. 



A survey of the types of carbohydrate metaboUsm in present living beings 

 shows their versatility and their complexity. It is now known that there are 

 various types of fermentation processes such as lactic acid, alcohol, propionic 

 acid, Clostridium type and Escherichia- Salmonella type of fermentations in refer- 

 ence to the varieties of end products shown in Scheme i. 



Scheme i 

 The versatility of fermentation types 



Sugars 



\ 

 Glucose 



I 

 EMP System 



I 



CHsCHOHCOOH^ Pyruvic acid CH3COCOOH 



Lactic acid 

 Fermentation 



Alcohol Fermentation 



CHaCHaCOOH 



Propionic acid 

 Fermentation 



4 

 Acetic acid CH3COOH 

 (Fermentation of Escherichia- 

 Salmonella Type) 



Butyric acid 

 CHaCH.CH.COOH 



• (Fermentation oi Clostridium 

 Type) 



