NUTRITION OF THE AUTOTROPHIC BACTERIA 77 



{a) via carbon monoxide, 

 OH 



2H 



cIh 



(h) via formaldehyde, 



OH H 



I \ 



C = + 2H, > C=0 + 2HoO 



(c) via formic acid, 



OH OH 



I I 



C = + H, > C = + HoO 



I " I 



OH H 



By analogy with plant metabolism it would be expected 

 that the second method, via formaldehyde, is the most 

 probable. Support is lent to this view in that formalde- 

 hyde can be fixed as an insoluble complex with dimedon 

 (see Chapter XV) in the cases of Nitrosomonas and an 

 autotrophic sulphur oxidising organism. 



Van Niel has suggested that all photospithetic 

 reactions in which carbon dioxide is reduced conform to 

 the general equation : — 



light 

 CO2 + 2H,A > (CHoO) + 2A + H./J. 



In the case of green plants HgA is water and oxygen is 

 set free. In photosynthesis by bacteria H2A may be 

 one of a variety of inorganic or organic substances 

 characteristic of the particular organism. It is assumed 

 that each of the necessary four quanta of light energy 

 is associated with the activation of a hydrogen atom in 

 the pigment and that the carbon dioxide is reduced by 

 the activated pigment which thus becomes re -oxidised. 



