Evolution in action

Seeing is believing, so it is good to see evolution in action. The above movie shows a huge petri dish with bacteria starting at both edges where there is no antibiotic. The dish has a gradient of increasing concentration of this antibiotic towards the centre of the plate. Initially they can’t grow in the regions where the antibiotic concentration is high. But they evolve resistance and just march up the gradient of the antibiotic. This takes about two weeks. Impressive.

The plate is an inspired, simple idea, by Michael Baym and coworkers. People have been studying evolution of bacteria for decades, but this is not only a beautiful way to see it, but it shows some lovely patterns of growth.

In a number of places you can see the (appearing as white) bacteria growing out from a point. Presumably, a single bacteria underwent the key mutation that pushed its antibiotic resistance up high enough to survive in a new region, and its descendents rapidly grew into the region, so a new white blob fanning out from a point may all be daughters, granddaughters, …, of a single bacterium. E. coli can reproduce to form two daughter cells every 20 minutes in ideal growth conditions. This means that in 24 hours, one bacterium can give rise to a billion trillion (1021) daughters.

You can also see competition between the blobs growing out, some grow to larger areas than others. A beautiful illustration of some evolutionary pathways succeeding at the expense of others. All in all, a lovely piece of work.

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