Chemotaxis- Bacterial Movement!

Still don’t have any faster way to get online (again posting from Nokia N72 using Vodafone GPRS!) but I’m expecting to get a broadband connection installed at my home by this Monday.
And I discovered the answer to that question in that book itself. Here’s the solution-
For distinguishing a Procaryote from Eucaryote without using a Microscope, the phenomena of “Chemotaxis” may be considered.
Bacteria, falls under Procaryotes shows movement towards certain chemicals known as “Attractants” also they show movement away from some chemicals, named as “Repellents”.
This type of behavior is shown by bacteria only.

1:-Take a capillary tube, fill it with some proper attractant & place it over a bacterial suspension. On diffusion of attractant from the end of the capillary, bacteria will swim up that capillary tube.
Number of bacteria in that capillary tube will determine the strength of attractant & rate of chemotaxis.

2:- If bacteria are placed in the centre of a petri dish of a semisolid agar containing an attractant, the bacteria will exhaust the local supply & then swim outward following the attractant gradient they have created. Result is expanding ring of bacteria.
And when a disk of repellent is placed in a petri dish of semisolid agar & bacteria, the bacteria will swim away from repellent, creating a clear zone around the disk.


3 thoughts on “Chemotaxis- Bacterial Movement!

  1. Sentences written about the attractants and repellents and their only observed effect in bacteria is MISLEADDING!
    However, both types of chemotactic ligands are acting in a very characteristic way in procaryotes (see well described activation of receptors and the downstream signalling processes in the cell) – the attractants and perellents are working in the same way in eucaryotic unicellular or multicellular systems (e.g. ciliate Tetrahymena or WBCs).
    Chemotactic responses are well characterized using different chemotaxis assays (e.g. capillary test or Boyden chamber assays) – and we can clearly distinguish chemoattractants like IL-8, RANTES or other chemokines and chemorepellents like aromatic amino acids(Tyr, Phe, Trp), melatonin etc.
    The above described data of the literature prove that the sentence of the text above “This type of behaviour is shown by bacteria only” is far from the correct descroption of the phenomenon.

  2. I’m completly relying on Prescott, Harley & Klein’s Microbiology for this also got that question in that book at the back of the chapter of Procaryotes. And according to this book chemotaxis is the only explaination to that question!
    Would you please explain me if there’s any other way to distinguish between these two types of cells without a microscope?

  3. Dear Ankit,
    I am happy with your rapid response.
    I have found your blog as I am working on the filed of chemotaxis research in the last 25 years -which makes basically nothing, but perhaps helps to find a more adjusted view of the problem discussed by you.

    Your text suggests that chemotactic responsiveness is the only one which provides the possibility to distinguish Eukaryotic and Prokaryotic cells via responsiveness to attractants and repellents.

    Your text is right only in parts as:
    1. There are some chemotaxis assays which evaluation does not require microscope. However, some of them are VERY rough (see agar plate assays), the others are based on molecular biological tools (so they are not simple but more-more difficult!)

    2. The problem is that these chemotaxis assays are suitable for prokaryotic cells as well as eukaryotic cells … and

    3. The ligands (either attractants or repellents) are working in the same or similar manner on the two levels of the phylogeny !

    In summary: neither the assay (even it is a microscopic or not) nor the ligand, does not warrants making sure distinguish between the two kinds of cells.

    You have cited the book of Prescott et al.
    Sometimes the books are also false in some respect – especially when they are getting old in some chapters.

    I hope I could make it more clear then it was at the first time on your page.
    Nevertheless, please ask me or tell me your objectives if you feel that something is in conflict with your books or lectures.

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