denitrifying bacteria

denitrifying bacteria: see nitrogen cycle.

Soil microorganisms whose action results in the conversion of nitrates in soil to free atmospheric nitrogen, thus exhausting soil fertility and reducing agricultural productivity. Without denitrification, earth's nitrogen supply would eventually accumulate in the oceans, since nitrates are highly soluble and are continuously leached from the soil into nearby bodies of water. Seealso nitrifying bacteria.

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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 nitrase reductase enzyme, to turn oxides back to nitrogen gas or nitrous oxides for energy generation. This process takes place only in the absence of oxygen, as most denitrifying bacteria are essentially anaerobic and the nitrase reductase can only be synthethised under anaerobic circumstances. This is the main reason why denitrification mostly occurs in the deep substrata of the soil, or in areas of stagnant water.

This process of denitrification lowers the fertility of the soil and thus is less common in areas where the land is rather well-cultivated. But this loss of nitrogen to the atmosphere can eventually be regained via introduced food and water, as part of the nitrogen cycle. Some nitrogen may also be fixated by species of nitrifying bacteria and the cyanobacteria.

Denitrification also becomes the key pathway for dissimilation, which is the process in which nitrates are reduced from the soil, the former being highly toxic for living organisms. Unlike its antithesis, denitrification tends to produce large amounts of by-products.

The most common denitrification process is basically outlined below, with the nitrogen oxides being converted back to gaseous nitrogen (as opposed to that of nitrifying bacteria):

2NO₃^- + 10e^- + 12H⁺ → N₂ + 6H₂O

As can be seen, the result is one molecule of nitrogen (consisting of two atoms) and six molecules of water.

Denitrifying bacteria themselves include several species of pseudomonas, alkaligenes and bacillus. By their activity the losses of nitrogen into the atmosphere is roughly balanced by that which is released into the soil by nitrifying bacteria, forming the relatively reliable cycle.

Denitriying bacteria

A Group of bacteria that reduce nitrates or nitrites to nitrogen-containing gases. Potential examples includeThiobacillus denitrificans, Micrococcus denitrificans/Paraoccus denitrificans and Pseudomonas. This is important as it allows Nitrogen to cycle (see Nitrogen cycle) back into the atmosphere.

These bacteria have also been implicated in depletion of soil fertility, and thereby agricultural productivity.

See also

Nitrogen cycle