by Christoph
As before in Lost & Found #1–6, here are three bookmarks again that caught my eye when I was cleaning up our account on 𝕏 (formerly Twitter). And which might still be worth a quick look for you, too, I hope, so here it is Lost & Found #7.
Bookmark #1
It has become a popular test for biofilm researchers to study the motility – twitching and/or swarming motility – of their bacteria in soft agar. P. aeruginosa is particularly good at growing from the center not just in a circular front towards the edge of the Petri dish, but forming branches as it swarms. When asked, Varsha Singh replied that the timer shown in the video gives hours:minutes.
Here is a dance for you. Feel free to identify the organism and the pattern. pic.twitter.com/w1suO4xiLv
— Varsha Singh PhD (@VarshaS53228024) October 14, 2021
If the tweet is no longer available, you can see a screen capture here, and the video here (GIF).
The reader @LizSquared was reminded of the works of Inuit artist Kenojuak Ashevak by the pattern conjured up by the Pseudomonas cells on the Petri dish; here is an example.
Bookmark #2
Swarming assays in soft agar on Petri dishes are also an excellent way to choreograph a pas de deux. In this video from the Varsha Singh lab, you can see Pseudomonas (left) and Klebsiella (middle) each doing a solo, and then a pas de deux (right).
Do you know that Pseudomonas aeruginosa (Pa) can push its competitor, Klebsiella pneumoniae, away? Here is a movie to show you how. @pseudocap @pseudo_papers
Read more in our preprint https://t.co/PxMgr6kMhU pic.twitter.com/90GvwJqnOJ
— Varsha Singh PhD (@VarshaS53228024) September 24, 2022
If the tweet is no longer available, you can see a screen capture here, and the video here (GIF).
Pradhan et al. (2022) write in the abstract of their preprint: "We find that P. aeruginosa employs neither proteases nor toxic secondary metabolites against K. pneumoniae. Rhamnolipid biosurfactant appears to be the only factor required to displace Klebsiella effectively. Both rhamnolipid production and the pushing ability of P. aeruginosa are suppressed by iron supplementation. We show that both these bacteria produce several siderophores in minimal medium and rapidly deplete iron. Under these conditions, P. aeruginosa pushes Klebsiella away from the substratum using rhamnolipid, reducing the competition for iron."
Bookmark #3
Did you know that it has been known for over a century that it is the chloroplasts in algae and plant cells that produce oxygen during photosynthesis?
Today in ingenious historical experiments: Theodor Engelmann demonstrated that chloroplasts are the site of oxygen production in plants by taking bacteria that would migrate towards oxygen and seeing that they went to the choloroplast
(from Howard Berg's "E coli in Motion") pic.twitter.com/jNSEUrktUs
— Adam Strandberg (@strandbergbio) December 21, 2022
If the tweet is no longer available, you can see a screen capture here, and a slightly better reproduction of the image here.
In his book E. coli in Motion, Howard Berg wrote in the chaper on Engelmann's experiments: "…Then he had a bright idea: use cells that like oxygen as analytical chemists to indicate where oxygen is generated in a green plant during photosynthesis. The answer proved to be the chloroplast. Engelmann reviewed these experiments in 1894. Figure 2.2 shows one of his drawings of an agal cell called Spirogyra that has a spiral chloroplast. When the cell was illuminated with a spot of light, as shown on the left, the bacteria accumulated near its surface but only if the spot impinged on the chloroplast. If the cell was illuminated uniformly, the bacteria accumulated in a spiral array." (here is a slightly better reproduction of Figure 2.2)
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