Day 4 - Extra Tests on Our Unknown Bacteria

Today we did some additional tests to determine some properties of our bacteria.

Oxidase Respiration Test:
This test determines whether our bacteria has cytochrome oxidase, which helps with electron transport during respiration.  Cytochrome oxidase helps attach electrons to oxygen or to nitrogen when oxygen is not available.  But not all bacteria that grow in oxygen have cytochrome oxidase.

Materials:
Oxidase reagent
Piece of filter paper
Pure culture of our unknown bacteria on an agar plate
Petri dish lid

Steps:
1.  Clean the top of the Petri dish lid with alcohol so it is sterile. 
2.  Set the piece of filter paper on the lid and saturate it with the oxidase reagent.
3.  Using aseptic technique, transfer some our bacteria to the saturated filter paper.
4.  Observe for the appearance of a purple color.

Result:  We did not observe a purple color, so we had a negative test result.

Discussion:  Based on the result, our bacteria does not contain cytochrome oxidase.  This does not mean that our bacteria does not grow in oxygen.  Our bacteria just does not have this enzyme.




Hydrogen Peroxide:
Organisms that use oxygen as the electron acceptors in cellular respiration have an enzyme called catalase, which breaks down hydrogen peroxide.  This reaction produces the bubbles that are seen when hydrogen peroxide is poured on an infected wound.  Anaerobic bacteria do not have catalase, since they do not use oxygen.  Thus, the hydrogen peroxide will kill those bacteria, because they cannot break it down.



Materials:
Pure culture of our unknown bacteria on agar plate
Hydrogen peroxide








Steps:
1.  Uncover our agar plate and pour enough hydrogen peroxide to cover the surface.
2.  Watch to see if bubbles form.

Result:  Positive result, since bubbles formed.





Discussion:  Since we have a positive result, our bacteria can use oxygen in respiration.