How are organisms like Pseudomonas and Thiobacillus of great significance in nitrogen cycle ?

Explanation

In biological nitrogen fixation, the atmospheric `N_(2)` gets reduced to `NH_(3)` by nitrogenase reductase present in some prokaryotes. `NH_(3)` is then oxidises to `NO_(2)` and `NO_(3)` by some other bacteria (Nitrosomonas and Nitrobacter). Various steps involved in nitrogenfixation are as follows

Pseudomonas and Thiobacillus are involved in the process of denitrification. They convert nitrate `(N_(3)^(-))` and nitrite `(NO_(2)^(-))` into free nitrogen `(N_(2))`, which is released into the atmosphere.