Denitrifying bacteria form a necessary part of the process known as denitrification as part of the nitrogen cycle, their primary purpose being to metabolise nitrogenous compounds, with the assistance of the nitrate reductase enzyme, to turn oxides back to nitrogen gas or nitrous oxides for energy generation.
Gram-negative bacteria | Gram-positive bacteria | Sulfate-reducing bacteria | Siderophilic bacteria | Shown above as a result of a 7 week period where the columns have been allowed to grow algae, cyanobacteria and other bacterial colonies. Of specific interest are the red regions of the middle column, indicative of purple non-sulfur bacteria (e.g. ''Rhodospirillaceae | gram-positive bacteria | ''E. coli'' bacteria | Coliform bacteria |