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Environmental Influences: Oxygen Concentration

Background and Introduction:

Bacteria vary considerably in their requirements for oxygen.  Molecular oxygen (O2) is usually thought to be necessary for life.  This is not always the case, however, since many microorganisms thrive in the absence of O2 and some microorganisms are actually inhibited or killed by toxic derivatives of this gas.  According to their O2 requirement, bacteria are classified as: 

  • aerobes:  organisms that require atmospheric O2 for growth. 

  • anaerobes:  organism that are killed or inhibited by the presence of atmospheric O2. 

  • facultative anaerobes:  organisms that do not require O2 for growth, but do grow better when it is present. 

  • microaerophiles:  organisms that require low concentrations of O2, generally between 2 and 10%. 

  • aerotolerant anaerobes:  anaerobic organisms that can survive in the presence of O2, but do not use it in their metabolism. 


OXYGEN CONCENTRATION: Four microorganisms from the following list will be tested for growth in Brain Heart Infusion (BHI) agar deeps. 

Test Organisms:Bacillus subtilis 
Escherichia coli 
Campylobacter jejuni 
Clostridium sordellii 

1. Using tape, prepare a label for 4 tubes with your initials, lab section, and each of the test microorganisms. The BHI agar deeps are kept in a hot water bath so that the agar will remain molten (liquid) until inoculation.  Remove one tube at a time from the water bath, place the label on it and then follow the stab tube technique   

2. Disperse the organisms throughout the molten agar by rotating the tube between the palms of your hands.  DO NOT Shake Cultures. 

3. Place the tubes in the rack on the side lab bench to incubate at 37˚C for 24 - 48 hours.


Observe and compare the growth of Bacillus subtilis, Campylobacter jejuni, Clostridium sordelli, and Escherichia coli.

tube growth of Bacillus subtilistube growth of Campylobacter jejunitube growth of Clostridium sordellitube growth of E. coli

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