What processes in the nitrogen cycle are completed by bacteria decomposers

In the Nitrogen cycle there are basically four steps and bacteria is involved in three steps of the N-cycle namely - Nitrogen fixation, Ammonification and De-Nitrification.

The Decomposers bacteria are involved in the ammonification process, where they convert organic waste, rich in nitrogen into simpler compounds usually ammonia which is further broken down into nitrite and nitrate. This process usually occurs in the absence of light and oxygen by anaerobic/facultative bacterias.