Thank you, Saverio! It was a fun experiment, indeed, and there's so much more to explore :)

It was fun to uncover this story—bridging microbial physiology, biological pattern formation, & active matter physics. The results may even have implications for controlling microbes in applications. We'd love your feedback. Please report/share with whoever might be interested! [8/8]

Many biological fluids are polymer solutions, whose viscoelasticity can enhance cell swimming and promote large-scale mixing.
We showed that the core-shell organization also arises in polymer solutions, but with fascinating additional flow fluctuations. [7/8]

We then developed a biophysical model describing this interplay quantitatively. The model recapitulates the experiments, and also yields criteria for predicting the different ways in which confined bacterial populations self-organize under different conditions. [6/8]

Cells consume O2, creating a gradient that alters motility: (i) They move up the gradient toward the droplet boundary via aerotaxis, & (ii) They stop swimming in the anoxic droplet core and accumulate. These motility variations in turn reshape O2 fluxes. A feedback loop! [5/8]

By simultaneously measuring cell distributions, oxygen concentration, and swimming-generated fluid flow, we figured out that this spatial organization is driven by the interplay between cell metabolism-generated oxygen gradients and collective motility. [4/8]

Surprisingly, when the droplets are big and concentrated, the cells self-organize into a concentrated inner "core" of immotile cells surrounded by a more dilute outer "shell" of highly motile cells. (See movie in 1st tweet.) In some cases, the core shrinks and disappears. [3/8]

Bacteria often inhabit confined spaces, such as biological tissues/gels & soils/sediments, where metabolites are scarce. What influence does confinement have on a population of motile bacteria?
We addressed this question by studying quasi 2D droplets of swimming E. coli. [2/8]

Can I please be added here?

This is a beautiful work Nico! Congrats!

Can I please be added here?