Can we quantify the impact of oxygen on the growth of a bacteria ?
-By Adrien Vergès
Every living being needs to produce energy to survive. To do that, they all do respiration (cellular or physiological respiration) to transform some physical elements to other extracting energy from the first. For example, we, as human being, breathe oxygen but for other oxygen isn’t necessary at all, it can even be toxic. For some bacteria called anaerobic, the respiration takes another shape than ours : fermentation. My work consisted in quantifying the growth of one type of bacteria,Escherichia coli, in function of the rate of oxygen.
Fig 1 : Different types of bacteria
1: obligate aerobes
2: obligate anaerobes
5: aerotolerant bacteria (homogenous concentration)
First how could I change the rate of oxygen in a limited volume ? Nothing that was available would have allowed me to change precisely the concentration of oxygen, that is why i decided to use a flame to burn a part of the oxygen. My limited volume would be played by a jar in which i would let a candle burn . Why a candle ? Because I also had to prevent the flame from burning all the oxygen to have differents concentrations between a jar where there would no oxygen and one with a normal concentration ( 20% which is the atmospheric concentration). The candle burns slowly in comparison with a Bensen burner, it let the time to stop the flame before it has burnt all the oxygen.
There is no evidence that oxygen plays a role in the growth development of E. coli according to the graphs. Indeed the size of the colonies is the the same when the plates have grown in a normal concentration of oxygen and in no concentration of oxygen.
What can we conclude here ?
Here there is no conclusion to bring because we do not observe any change when the variables “concentration of oxygen” changes. Furthermore I choose a bacteria that is not influenced by oxygen because E. coli can do respiration with oxygen and without (fermentation). Next time I will work with a obligate bacteria to know if my experiment is well designed because I would be able to expect a result (no growth when there is a lack of oxygen).
