Name the various organisms involved in the nitrogen cycle.

(N/A) $(i)$ Nitrogen-fixing bacteria,$e.g.$,$Rhizobium$,$Azotobacter$.
$(ii)$ Bacteria that convert complex nitrogenous organic compounds (proteins) into ammonia,$e.g.$,$Actinomyces$.
$(iii)$ Nitrifying bacteria that convert ammonia into nitrates,$e.g.$,$Nitrosomonas$ and $Nitrobacter$.
$(iv)$ Denitrifying bacteria,$e.g.$,$Pseudomonas$.