Denitrifying bacteria widely exist in various forms in nature, such as: Paracoccus denitrifying (autotrophic, hydrogen peroxide H2) Thiobacillus denitrifying (autotrophic, sulfide oxidizing or thiosulfate (S2O3)) Pseudomonas schrenckii (heterotrophic, organic carbon oxidizing). Denitrifying bacteria are mainly prokaryotes, and a large number of α-known denitrifying bacteria are achromobacter, Acinetobacter, Agrobacterium and Bacillus.

Microbial absorption and utilization of nitrate have two completely different purposes. One is called assimilation nitrate reduction with nitrogen as nitrogen source: NO3-→NH4+→ organic nitrogen. Many bacteria, actinomycetes and molds can use nitrate as nitrogen nutrition.

Another purpose is to reduce nitric acid to nitrogen (N2) by using NO2- and NO3- as the final electron acceptors of respiration, which is called denitrification or denitrification: NO3-→NO2-→N2↑. Only a few bacteria can carry out denitrification, and this physiological group is called denitrifying bacteria. Most denitrifying bacteria are heterotrophic bacteria, such as denitrifying micrococcus and denitrifying Pseudomonas. They use organic matter as nitrogen source and energy source for anaerobic respiration.

A few denitrifying bacteria are autotrophic bacteria, such as Thiobacillus denitrificans, sulfur oxide or nitrate to obtain energy, assimilate carbon dioxide, and nitrate as the final electron acceptor of respiration.