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

Organisms like Pseudomonas and Thiobacillus are significant because they perform the process of denitrification.
In this process,these bacteria reduce nitrates $(NO_{3}^{-})$ and nitrites $(NO_{2}^{-})$ present in the soil back into gaseous nitrogen $(N_{2})$.
This nitrogen is then released back into the atmosphere,thereby completing the nitrogen cycle.