THE CYCLES 



375 



Atmospheric nitrogen 



Nitrosomonas 



Ammonia 



CI. zvelchii 

 Desulpkovibrio, etc. 



"Nitrite 



Bacterial proteins 

 (autotrophes and heterotrophes) 



Nitrate 



Fig. 102 — Microbial nitrogen cycle. 



Bacterial oxidation 



Sulphur 



HgS 



a 



Bacterial oxidation 



Bacterial desulphuration 



Sulphates 



*o. /\ S of plant organic compounds 



Excreta 



S of animal organic compounds 



Urine 



Fig. 103— The sulphur cycle. 



