Bacterial growth (plotting data)

Lesley Robertson L.A.Robertson at stm.tudelft.nl
Thu Sep 21 02:36:28 EST 1995

Frank Pietrantonio <XPII at MUSICB.MCGILL.CA> wrote:
>Is it neccessary to plot growth (aborbance vs. time) on a semi-log scale?
>I agree that plotted data on semi-log gives a better representation of 
>growth rate.If one were to describe and compare the amount of growth per 
>set time in the growth cycle would plotting the data on a normal scale be 
>adequate? I would like to compare the amount of growth using two 
>different substrates but at the same set time in growth. Plotting the 
>data on semi-log does not give a very good comparison. If anyone out 
>there can help please e-mail me. 
>                                        Thanking you in advance,
>                                         Frank Pietrantonio
>                                          xpii at musicb.mcgill.ca

It depends what the aim of the experiment is. Most people like to 
calculate maximum specific growth rates (or doubling times) from their 
batch culture data. This can only be done during the log growth phase, 
and that is best recognised because you get a straight line on a semi-log 
plot. If there's a problem with the culture (some sort of inhibition, 
perhaps) you won't get log growth, and no straight line. There's no 
tablet of stone saying you have to use semi-log, if you want to use 
something else, or it shows your data better, go for it! If you want to 
compare AMOUNT of growth rather than RATE of growth, you'd be better 
doing biomass measurements (protein, dry weight, etc) and many things can 
interfere with optical density (e.g. precipitates).
I guess my answer is "define the aim of the experiment, then choose the 
most appropriate means of measurement and data handling". HOWEVER, if 
your supervisor has told you to do it in a specific way, DON'T change the 
method without discussion - there may be good reasons for the selection 
of that method.
Dr. Lesley A. Robertson
Kluyver Laboratory for Biotechnology
Delft University of Technology, the Netherlands
L.A.Robertson at stm.tudelft.nl

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