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The Fascinating Journey of Chemotaxis: From Ancient Discoveries to Modern Insights

Embark on a historical journey through the evolution of understanding chemotaxis in bacteria, from the discoveries of Anton van Leeuwenhoek to Julius Adler's breakthrough in 1969. Explore how E. coli responds to attractants, the role of metabolism, and the molecular mechanisms behind chemotactic signaling pathways. Witness the marvel of bacterial motility in the face of physical constraints, shedding light on their remarkable swimming abilities. Join this captivating exploration of a fundamental biological phenomenon.

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The Fascinating Journey of Chemotaxis: From Ancient Discoveries to Modern Insights

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  1. Chemotaxis and motility

  2. ~400,000 years Homo sapiens ~2M years Homo erectus 3.6 B years 1678 AVL ~400 years 1836 Ehrenberg Chemotaxis Read Berg, Chapter 2 ~200 years 1881: oxygen and light Engelmann

  3. Anton van Leeuwenhoek (1632 -1723) “I now saw very plainly that these were little eels, or worms, lying all huddled up together and wriggling; just as if you saw, with the naked eye, a whole tubful of very little eels and water, with the eels a-squirming among one another: and the whole water seemed to be alive with these multifarious animalcules. This was for me, among all the marvels that I have discovered in nature, the most marvelous of all; and I must say, for my part, that no more pleasant sight has ever yet come before my eye than these many thousands of living creatures, seen all alive in a little drop of water, moving among one another, each several creatures having its own proper motion”.

  4. (Original image was a hand-drawing) Pfeffer assay (1884): Congregation of bacteria at mouth of capillary containing meat extract

  5. 80 years later…. 1969 Julius Adler describes chemoreceptors in bacteria, a discovery demonstrating that bacteria can sense and process environmental information. His method involved inserting a tube of chemicals into a solution of bacteria and then counting the number of bacteria that swam to the chemical. "That's one small step for a man, one giant leap for mankind."

  6. Adler introduced the quantitative capillary assay, ushering in the modern era of chemotaxis 10 mM phenol 10 mM L-serine Attraction and repulsion Read Berg, Chapter 3

  7. A kid in a candy store

  8. Summary of Adler’s experiments (1969) Q: What is E. coli attracted to? 1. Defined chemicals were tested as attractants. Galactose Ribose Aspartate Serine Chemotaxis towards glucose but not toward glycerol

  9. Q: Is attraction related to the ability to metabolize the chemical? What would be a simple way to test if an attractant was being metabolized? 2. Attractants were metabolized, but not all metabolized chemicals were attractants For example, both glucose and glycerol are metabolized, but only glucose is an attractant

  10. Q: For attractants identified, was metabolism essential? Galactose Ribose Aspartate Serine 3. Attractants could be metabolized, but metabolism was not necessary.

  11. Q: Do non-metabolizable analogs attract? 4. Attractants could be metabolized, but metabolism was not necessary.

  12. E. coli pays attention to things of low mw, among them oxygen, acids and bases, sugars, amino acids and dipeptides. Taste will do. Consumption is not necessary. Howard Berg ‘E. coli in Motion’

  13. Q: How are the attractants being recognized? 5. Genetic evidence for external receptors for attractants. 6. Receptors recognize structure of attractants.

  14. Q: How many receptors? Fucose/galactose galactose Aspartate/serine serine Structurally related compounds compete 7. Evidence for structural recognition of attractant by receptors, and for different classes of receptors.

  15. Receptors have specificity Gal BP-Trg Glu BP–Trg Rib BP -Trg Tar Tsr 8. Five different classes of receptors. How can you test this conclusion?

  16. What if there were mutants that did not respond to all five attractants? Non-chemotactic point mutations 9. First molecular scheme for how chemotaxis might work.

  17. Plate assay for chemotaxis Che- Wild-type LB (nutrient-rich) soft agar (0.3%) Read Berg, Chapter 3

  18. Swimming E. coli 3D Random Walk Fluorescent Anti-antibody EM

  19. Darkfield Microscopy (1976) Run-Tumble

  20. Helical transformations in fluorescently-labeled flagella (2000) Alexa fluor dyes Rowland Institute at Harvard – Howard Berg

  21. The chemotaxis signaling pathway in E. coli/Salmonella CW CCW CCW CCW CW Taken from various reviews

  22. Small size, big problems The miniscule size of bacteria consigns them to a life that is dominated by viscous drag and Brownian motion. (An equivalent scenario would be a human trying to swim in a pool of molasses.) Their small mass confers such little momentum, that if the flagellar motors of an E. coli cell were to stop turning, water viscosity would bring the cell to a full stop after a coasting distance of less than 1 Å. Yet, despite these daunting physical constraints, E. coli cells swim at speeds of 10-20 body lengths per second. Amazing. Taken from J. Parkinson

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