If I have multiple points where it is linear, should I use all the points that are linear to account for the calculation of specific growth rate?
Also, how linear should the line be? what are the parameters of the linearity? Is it too strict to use a R(squared) of equal to 0.99 and above as measure for linearity?
Hi there,
If your data are OK you should trace a single line. So the issue is to consider the largest set of data giving an R2 close to 1.
For biological systems R^2 values above 0.98 is fine. However, you must ensure the absence of any diauxic phase in which case trend (for second lag phase) might continue for 2 or more multiplication cycles before being exponential again.
Yes, Square value helps to get linearity in graphs or any mathematical model. Higher R square value is desirable to establish linearity.
Take into consideration that the ghrowth depends always on a number of other factors, such as solubility of the substate: A really linear growth, meaning non-exponential, you will find when growing bugs with very little water-soluble compounds such as PAHs or other more lipophilic compounds (here, the bacterial growth rate depends on the velocity of solubilization of your substrate), whilst exponential growth can be obtained when using highly water-soluble compounds, such as organic acids (at neutral or slightly basic pH), or sugars.
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