Bacterial Growth

How can you account for the observation that a mass of bacterial

growth shows pigmentation while the individual cells have transparent


Request for Question Clarification byblazius-ga

By "a mass of bacterial growth", do you include the growth medium and

possible excreta from the bacteria, or would you only consider the

bacteria cells?

One thought on “Bacterial Growth

  1. There are at least two ways to approach your question:

    1) If you are referring to the fact that a pellet (or "mass") of

    bacterial cells after centrifugation is visible, while the cells

    individually are not, aceresearcher's 2nd answer is quite correct –

    it's not that the individual cells are colourless, it's just that

    there isn't much substance to their coloured bits and so, individually

    there isn't enough colour to perceive with the naked eye (until you

    pack all the cells together). A common technique for estimating the

    quantity of bacteria in a culture is to use a spectrophotometer (a

    device that shines a light through a sample and can detect small

    differences between the amount of light put it versus the amount which

    comes out, thus giving you the amount absorbed by the sample) to

    measure the small amount of colour that the bacteria do have. A nice

    site illustrating this:

    2) Some bacteria only express certain proteins when there are enough

    other bacteria around – this is an effect called "quorum sensing" and

    results in large colonies of bacteria acting in concert to change

    their behavior when a certain growth density is achieved. Pigment

    proteins may be among those proteins only expressed when a certain

    density is achieved. This effect may be multiplied by the effect

    above, such that large quantities of bacteria expressing pigment due

    to their density become quite visible upon pelleting.

    A couple of sites which discuss quorom sensing and pigment expression:

    Quorum sensing:

    Paper on bacterial diversity, search page for quorum sensing for

    section on luciferase (luminescent pigment) production:

    fairly technical paper on pigment and quorum sensing:

    I hope this answers your question.


Leave a Reply

Your email address will not be published. Required fields are marked *