What is point of Durham tubes in a Nitrate reduction test?

In summary, the conversation is about confusion with the lab manual's instructions for testing for nitrate reductase activity. The confusion arises from contradictory statements regarding the use of Durham tubes and the presence of gas in them. The manual states that if gas is present, the test is complete, but later advises adding reagents to all tubes regardless of gas presence. This raises questions about the purpose of using Durham tubes if they may not accurately indicate the presence of nitrogen.
  • #1
Lab manual is confusing me, and I'm not sure if its actually wrong, or the wording is bad, or if this is because I'm not understanding something.

It says:

"Before a broth can be tested for nitrate reductase activity it must be examined for evidence of denitrification. This is simply a visual inspection for the presence of gas in the Durham tube. If the Durham tube contains gas, the test is complete. Denitrification has taken place"

then 4 paragraphs later it says this:

"One or more of the organisms selected for this exercise are fermenters and possible producers of gas other than molecular nitrogen; therefore you will proceed with adding reagents to all tubes."

So why does the manual say that the test is complete if I see gas in the durham tube, while the next paragraph tells me to proceed adding reagents to all tubes. regardless of gas in the durham tube?

And that makes me then question what the point of using the durham tubes is; As I understand this, the gas in durham tube could be a number of different gases other than N2, but denitrification produces N2, doesn't it? So if the gas in tube is unknown, what was the point of using durham tubes? It says some organisms are known fermenters, so the durham tubes seem pointless, with respect to testing for presence of nitrogen.

Thanks for any help
 
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  • #2
"Conditional" logic; "if this, then that." Unless it's Monday, in which case, "this" implies "something else."
 

1. What is the purpose of Durham tubes in a Nitrate reduction test?

The Durham tubes are used to detect the production of gas during the nitrate reduction test. This gas production is an indicator of the presence of nitrate reductase enzyme, which is necessary for the reduction of nitrate to nitrite.

2. How do Durham tubes work in a Nitrate reduction test?

The Durham tubes are filled with a gas-trapping solution, such as mineral oil or sterile water. When a sample containing nitrate reductase is added to the medium, if nitrate is present, it will be reduced to nitrite, which in turn is reduced to ammonia and gas. The gas produced is then trapped in the Durham tube, indicating a positive result for nitrate reduction.

3. Can Durham tubes be used in other types of biochemical tests?

While Durham tubes are commonly used in the nitrate reduction test, they can also be used in other tests that require the detection of gas production, such as the fermentation test. They can also be used in anaerobic culture methods to detect gas production by bacteria.

4. What is the advantage of using Durham tubes in a Nitrate reduction test?

The use of Durham tubes allows for a visual confirmation of gas production, which is a clear indicator of the presence of nitrate reductase. This eliminates the need for further testing and provides a quick and accurate result.

5. Are there any limitations to using Durham tubes in a Nitrate reduction test?

Durham tubes are only effective in detecting gas production from nitrate reduction. They cannot determine the specific type of bacteria present or the exact amount of nitrate that has been reduced. Additionally, if the gas produced is not trapped in the Durham tube, a false negative result may occur.

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