I filmed my first swarm on February 29, 2008. I placed the inoculated Petri dish under a video camera, inside a temperature-controlled room set to 37C. The camera took a picture at every 10 minutes for 24 h, which I then stitched into a 14 seconds long time-lapsed video. I had grown swarms before, but had not seen them move yet. I wanted to see how the dilute culture of bacteria spotted at the center each time developed into the branched colony in less than 24 h.

This was the first movie, and my lab members and I have made dozens since then. We used swarming as a model to understand how billions of bacteria behave cooperatively, moving together across distances >10,000x their body length in a few hours. Today we have a review in Annual Reviews Microbiology called “The Ultimate Guide to Bacterial Swarming: An Experimental Model to Study the Evolution of Cooperative Behavior”. The review talks about how we used the swarming assay to address evolutionary questions. It also tries to explain the difference between proximate mechanism and ultimate mechanism–I hope we have succeeded at that. Here’s an example: Proximate mechanism is for example when we determined that mutations in the gene fleN cause bacteria to become multi-flagellated and swarm faster than the wild-type. Ultimate mechanism is when we say that fleN-mutated hyperswarmers can’t exist in the wild because they are bad at making biofilms and should be disfavored by natural selection.

Read our review here:
The Ultimate Guide to Bacterial Swarming: An Experimental Model to Study the Evolution of Cooperative Behavior.
Jinyuan Yan, Hilary T. Monaco, and Joao B. Xavier. Annual Reviews Microbiology [online early]

See also Maxime’s paper where we proposed a new rule for evolution of faster dispersal at the edge of expanding populations. The paper was inspired by the hyperswarmers, and has many cool experiments with hyperswarming to test the new rule. The paper is now peer-reviewed and published in the American Naturalist.

Evolution at the edge of expanding populations.
Maxime Deforet, Carlos Carmona Fontaine, Kirill S. Korolev, Joao B. Xavier. The American Naturalist [in press-preprint on bioRxiv|early view at Am Nat]