452 FURTHER EVOLUTION 



out their activities at the boundary of a region where 

 ammonia is being formed anaerobically and one where it 

 comes into contact with the molecular oxygen of the air. 

 This may be observed in the soil, in sea water and in bogs."^ 



The iron bacteria, which oxidise ferrous to ferric salts, 

 develop especially luxuriantly where rich sources of iron 

 emerge on to the surface of the Earth. "^ 



At the present time very large amounts of hydrogen are 

 given off from the depths of the Earth and from wherever 

 the anaerobic decomposition of carbohydrates and proteins 

 is taking place. ^'^^ Bogs, especially, produce a considerable 

 amount of so-called marsh gas which contains hydrogen and 

 methane. In deeper waters the oxygen which penetrates into 

 them oxidises these gases as a result of the activities of hydro- 

 gen and methane bacteria and this often leads to the complete 

 disappearance of oxygen from the hypolimnion.^" 



Nowadays the chemoautotrophs play a very important part 

 in the circulation of materials. Practically all the processes 

 occurring under natural conditions leading to the oxidation 

 of reduced compounds of nitrogen and sulphur (and also 

 of hydrogen, methane and, to some extent, iron) are associ- 

 ated with the vital activities of the appropriate micro- 

 organisms. 



Table 5 is taken from S. Kuznetsov.^^^ It shows the 

 reactions carried out by the chemoautotrophs and the 

 organisms related to them. The equations given are, of 

 course, only those for the over-all reactions. The chemical 

 mechanism of these reactions has, as yet, only been very little 

 studied. At first it was believed that the metabolism of the 

 chemoautotrophs was very primitive."* However, as the 

 study of this field progresses, it becomes clearer and clearer 

 that it is far more complicated than the metabolism of ordin- 

 ary heterotrophs."^ 



A particular illustration of the great metabolic activity and 

 complexity of the chemoautotrophs is their ability to syn- 

 thesise various vitamins and growth factors. For example, 

 according to D. J. CKane,^''" T. thiooxidans can synthesise 

 thiamine, riboflavin, nicotinic and pantothenic acids, pyri- 

 doxine and biotin, i.e. almost all the members of the vitamin 

 B complex. This points, first of all, to a very great complexity 



