Newly Discovered Bacterial Crystals Are a Biophysics Mystery


Image: A. Petroff et al., Phys. Rev. Lett. (2015)
Image: A. Petroff et al., Phys. Rev. Lett. (2015)
Thiovulum majus is already a strange-enough form of bacteria.


By Michael Byrne|MOTHERBOARD

For one thing, it’s big, relatively speaking, existing as 5- to 20-micrometer spherical cells. The cells also exhibit some unique collective behavior—as residents of saltwater marshes surviving on oxygen harvested from the water, they often form into disordered clumps called veins, which allow the bacteria colony to circulate water like we circulate blood. They’re able to form these clumps thanks to a covering of tiny flagella, which also allow individual cells to swim faster than any other sort of bacteria.

As described in ​a recent paper in the Physical Review Letters, these bacteria are capable of yet another perplexing behavior—they form living two-dimensional crystals. Crystals, as we usually understand them, are tightly packed, periodic arrangements of atoms but, here, bacteria act as the atoms, forming into tight lattice structures thanks to the hydrostatic attraction produced by the bacterial flagella. This attraction is what takes the place of the electromagnetic force binding together proper crystals.

It was an unexpected discovery for the Rockefeller University-based research group. The plan was to study the movements of Thiovulum majus through water droplets on a two-dimensional slide and it was here that they noticed something strange. The bacteria, which have a proclivity for rotating as they move around, like tiny propellers, didn’t „bounce“ off of the surfaces they encountered as one might expect.

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