Successfully isolated pure cultures of the bacterium from soil. The anaerobic bacteria which grows under the soil is under the anaerobic condition and if these bacterial are under the nitrate broth they would require the nitrate as a nutrient for the growth. A heavy inoculum of test organism is incubated in a broth containing nitrate. These organisms are producing the nitrate reductase enzyme which can easily react on nitrate to get reduced into nitric oxide, nitrous, and nitrogen.
The nitrate reduction test is based on the detection of nitrite and its ability to form a red compound when it reacts with sulfanilic acid to form a complex (nitrite-sulfanilic acid) which then reacts with a α-naphthylamine to give a red precipitate (prontosil), which is a water-soluble azo dye.
However, only when nitrate is present in the medium, red color will be produced. If there’s no red color in the medium after you’ve added sulfanilic acid and α-naphthylamine means only that nitrite is not present in the medium.
There is two explanations for this observation.
Thus, when nitrite is not detected, it is necessary to test if the organism has reduced nitrate beyond nitrite. This can be done indirectly by adding small amount of Zinc powder to the culture. Zinc powder catalyses the reduction of nitrate to nitrite. The development of the red colour on addition of Zinc indicates that nitrate was not reduced by the organism which suggests that the test organism is not capable of reducing nitrate. If no color change occurs after the addition of zinc, this indicates that the organism reduced nitrate to one of the other nitrogen compounds and thus is a nitrate reducer.
The experiment was conducted with following steps:
Method
Determination of nitrate reduction to nitrite is a two step process.
On conducting the experiment the expected result obtained as follow:
You have successfully isolated pure cultures of a bacterium from soil. What result might you expect...
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