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<font size="+1">Test for reduction of NITRATE TO NITRITE</font size="+1"><BR> | <font size="+1">Test for reduction of NITRATE TO NITRITE</font size="+1"><BR> | ||
Develop the nitrate to nitrite test in the MNM tube by adding Gries reagent (2 drops of solution A, and then 2 drops of the solution B) to the surface of the medium. Nitrite-positive: The appearance of a pink or red coloration indicates that the nitrates in the medium have been reduced to nitrites. Be careful about interpreting negative reactions as evidence that the organism does not contribute to the nitrogen cycle. We already know that some of these bacteria perform at least one specific role in this crucial cycle. How? Hint: Think about the selective media you used to enrich for nitrogen fixers and ammonium users. Those media provided highly limited nitrogen sources. We have less information about nitrogen cycle contribution for your isolates that weren't selected on Azotobacter medium or Simmons citrate. We | Develop the nitrate to nitrite test in the MNM tube by adding Gries reagent (2 drops of solution A, and then 2 drops of the solution B) to the surface of the medium. Nitrite-positive: The appearance of a pink or red coloration indicates that the nitrates in the medium have been reduced to nitrites. Be careful about interpreting negative reactions as evidence that the organism does not contribute to the nitrogen cycle. We already know that some of these bacteria perform at least one specific role in this crucial cycle. How? Hint: Think about the selective media you used to enrich for nitrogen fixers and ammonium users. Those media provided highly limited nitrogen sources. We have less information about nitrogen cycle contribution for your isolates that weren't selected on Azotobacter medium or Simmons citrate. We can't test for all possible roles each of your isolates might contribute to this cycle. The Gries reagent test on those bacteria grown in MNM may give us evidence of one possible role they play, however, it is possible for bacteria that reduce nitrate to nitrite to give a negative Gries test because the nitrite produced from reduction of nitrate has been further processed and is gone by the time you do your testing. A positive test is meaningful but a negative test may not necessarily be evidence of incapability to reduce nitrate. No color change: Either the organism was unable to reduce the nitrate in the medium to nitrite or the nitrite was reduced to ammonia.<BR><BR> | ||
'''Gries reagent''' consists of solutions:<BR> | '''Gries reagent''' consists of solutions:<BR> | ||
'''Solution A'''<BR> | '''Solution A'''<BR> |
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