
Concept explainers
To review:
The bacteria appropriate for reducing nitrate concentration found in a sample of municipal sewage water.
Introduction:
Nitrates refer to the essential source of nitrogen for the plants. Nitrification is basically the biological oxidation of the ammonium or ammonia to nitrite, which is followed by the oxidation of the nitrite to nitrate. This transformation of ammonia to nitrite is generally the rate-limiting step of the nitrification. Whereas, denitrification refers to the loss or the removal of the nitrogen and compounds of nitrogen. Many bacteria help in this process of denitrification.
The table given below gives details of characteristics of four bacteria:
Name of Bacteria | Clostridium novyi | Thermus aquaticus | Paracoccus denitrificans | Trichodesmium thiebautii |
Characteristics | ||||
Obligate anaerobic | Obligate aerobic | Facultative anaerobic | Facultative anaerobic | |
Gram status | + | – | – | – |
Optimal temperature (°C) | 10–40 | 50–80 | 5–30 | 10–30 |
Typical habitat | Terrestrial | Aquatic | Aquatic | Aquatic |
Miscellaneous | Chemotroph | Denitrifier | Nitrogen fixer |
°C, Degree Celsius; (+), positive, (–), negative.

Explanation of Solution
According to the given statement, concentration of nitrate in municipal sewage water is very high, which is beyond the acceptable level. High concentration of nitrates can be reduced by the process of denitrification. This process is facilitated by denitrifying bacteria.
The facultative anaerobic bacteria Paracoccus denitrificans is the most appropriate bacteria for reducing nitrate concentration. In the process of denitrification, the bacterium reduces the nitrate to produce molecular nitrogen. This process is usually used in to reduce nitrate or nitrite concentration from sewage water.
Paracoccus denitrificans is a denitrifying bacterium and can survive in both organic and inorganic media. This bacterium performs the process of denitrification as a part of respiration, in which the nitrate is reduced in response to oxidation of an electron donor and finally the denitrification completed with the production of dinitrogen. During reducing nitrate, the bacteria produce intermediate products.
Therefore, it can be concluded that Paracoccus denitrificans is used to reduce the concentration of nitrates from the municipal sewage water. This bacterium is a facultative anaerobic organism and also a denitrifier.
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Chapter 25 Solutions
LIFE: THE SCIENCE OF BIOLOGY
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