A brief overview of denitrifying bacteria

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Denitrifying bacteria are anaerobic bacteria that belong to a diverse group of bacteria. That is capable of removing nitrogen ( denitrifying). These bacteria work in association with fungi & arachea. These bacteria remove nitrogen from nitrogenous compounds ( nitrates) present in soil into free nitrogen

 The diverse group of denitrifying bacteria represents 10- 15 % of the total bacterial population in soil, sediment & water.

Examples of denitrifying bacteria

  • Thiobacillus denitrificans
  • Micrococcus denitrificans

Some species of below-listed bacteria are also marked as denitrificans

  • Serratia
  • Pseudomonas
  • Achromobacter

Nitrogen cycle

It is essential to understand the nitrogen cycle first to make an understanding of denitrifying bacteria further. Thress major processes are involved in the nitrogen cycle, which is stepwise listed below.

nitrogen cycle
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1st step: Ammonification and nitrification

The 1st step of the nitrogen cycle involves the break down of organic compounds into ammonia. This process is termed ammonification. Ammonification is further followed by nitrification, in which nitrifying bacteria ( Nitrosomonas) convert this ammonia into nitrites. Nitrobactors also contribute to converting it further into nitrates.

2nd step: Consumption of  nitrates by plants

These nitrates are taken up by plants’ roots from the soils & convert them into aminoacid & protein & utilize them for their growth & development; this plant protein is later on taken up by animals & reconstituted as animal protein. The nitrogenous waste products produced by animal & dead bodies in soil served as an organic source for putrefying bacteria to again utilize its fo production of nitrites & nitrates; hence the cycle continues.


This process is not involved in the nitrogen cycle  & totally inverse of nitrification in which anaerobic bacteria use nitrates as an oxidizing agent instead of oxygen. As a result, no nitrates are available for being consumed by plants & in this way, the fertility os soil reduced.

Mechanism of denitrification

Denitrifying bacteria use the process of denitrification to generate ATP. Its mechanism is somehow lengthy but summarized in a most general & simple manner in the following steps.

  • In 1st step, nitrate (NO3) is converted into nitrite (NO2) with the help of an enzyme nitrate reductase.
  • In 2nd step, this nitrate is converted into nitric oxide (NO) by the enzyme nitrite reductase.
  • In the 3rd step, this nitric oxide is converted into nitrous oxide ( N2O) by the enzyme nitric oxide reductase.
  • In the 4th step, this nitrous oxide is finally converted into dinitrogen by nitrous oxide reductase.

Denitrifiers bacteria in forests

Forest presents the ecosystem with variant characteristics & therefore possesses different species of many animals, plants & microorganisms. The bacteria that serves as denitrifiers in forests include

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  • Alcaligenes
  • Pseudomonas
  • Bacillus species
  • Actinobacteria

Impact of denitrifying bacteria over the environment

Denitrifying bacteria exhibit some negative & positive impact over the environment & the ecosystem of a particular place. Their effects on plant productivity are one of the major problems that impart damage to that environment as well as soil

  • Denitrifying bacteria serve as a growth-limiting factor for plants by reducing soil fertility.
  • They cause the loss of nitrogen from soil & set them back to the atmosphere as free nitrogen.
  • By-products produced by denitrifying bacteria like nitric oxide & nitrous oxide are harmful to the environment as they deplete the ozone layer & increase global warming.
  • Denitrifying bacteria are used in wastewater treatment to remove ammonium compounds in the form of nitrogen gas.
  • They are also essential to maintain the level of nitrogenous salts & nitrates in the soil.

Aerobic denitrifying bacteria

Following the experiment & research, it is revealed by the source that under aerobic conditions, the majority of denitrifying bacteria are capable of producing nitrous oxide instead of dinitrogen. This study also shows that both notifying & denitrifying bacteria can produce N2O as a by-product in the absence of appropriate oxygen concentration. Denitrification is an anaerobic process, but it needs aerobic denitrifying bacteria to take over this duty in some situations. So To avoid confusion, we can say that when anaerobic bacteria are unable to catalyze the final product (N2) from N2) due to insufficient anaerobiosis, here anaerobic denitrification is followed by aerobic denitrification to remove dissolved oxygen & liberates N2O as a final product.

denitrifying bacteria
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Is denitrifying bacteria aerobic or anaerobic

Denitrifying bacteria are either facultative aerobes on anaerobes that can use denitrification as an alternative method of respiration.