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I have been reading some literature on measurements related to biofilms.

In some articles the word "substrate" seems to stand for the material on which a biofilm is growing. In other articles, it seems to stand for the nutrients that are freely floating in (say water) where the biofilm is growing, and which then diffuse into the biofilm and which it uses to grow.

Have I misunderstood something or are both of these meanings in active use? Is there a disciplinary or some other difference that determines who uses which term?

  • The review article [1] uses substrate to mean freely floating nutrietnts. Also, searching for "substrate loading" or "substrate loading rate" or such (on Google scholar) gives examples of substrate as something that is fed to the biofilm.
  • For example Wikipedia uses the other meaning of substrate: https://en.wikipedia.org/wiki/Substrate . Scientific literature with this meaning can be related to how easily biofilms detach from a given material in the presence of shear forces.

[1] Harald Horn and Susanne Lackner. Modeling of biofilm systems: A review. In Kai Muffler and Roland Ulber, editors, Productive Biofilms, pages 53–76. Springer International Publishing, Cham, 2014.

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    $\begingroup$ Latin: sub- underneath and stratum = layer... The under-layer literally, the base layer. $\endgroup$
    – bandybabboon
    Commented May 7, 2019 at 14:40

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A substrate is an underlying substance or layer, or less strictly, the medium within or upon which an organism grows. For instance, you can have a filamentous fungus grow on a solid medium (e.g. on an agar plate) or in liquid medium (e.g. in a shaken flask containing a solution) and its substrate would be the contents of the agar or solution. It's nothing more fancy than that.

For instance, you could design 4 growth conditions for a strain of fungus.

Case in point, a hypothetical table could look like this:

                        *Substrate*

                Wheat straw     Sugar beet pulp
                             |
          Liquid         1   |   2         
                             |
*Medium*             -----------------
                             |
           Agar          3   |   4

Simple!

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  • $\begingroup$ What is the interpretation of all the "substrate loading rate"s, then? Are they simply misusing the terminology? $\endgroup$
    – Tommi
    Commented May 7, 2019 at 19:13
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    $\begingroup$ @TommiBrander, no they are not misusing "substrate". Notice there are more words in the phrase "substrate loading rate". The phrase is referring to the the rate at which nutrients are loaded into the substrate. $\endgroup$
    – mgkrebbs
    Commented May 7, 2019 at 19:52
  • $\begingroup$ I edited in an explicit reference to a review article where "substrate" explicitly means diffusing nutrients, rather than the meaning mentioned here. $\endgroup$
    – Tommi
    Commented May 9, 2019 at 7:34
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    $\begingroup$ The nutrient can be the substrate. Leaves are a substrate for leaf-eating caterpillars. The skin of an orange is a substrate for mold. In these examples you'd use the word substrate rather than medium. As with all language, it doesn't help to be too pedantic about dictionary definition. The word 'nutrient' is also fuzzy but I would advise against opening a thread about the meaning of nutrient. Happy sciencing! $\endgroup$
    – S Pr
    Commented May 9, 2019 at 9:25

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