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Surprising, to say the least: Swirling Bacteria Linked to the Physics of Phase Transitions

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Gabriel Popkin writes in Quanta:

At first glance, the movie didn’t seem like much: a chaotic swarm of E. coli bacteria twiddling this way and that in a petri dish, seemingly at random. Such scenes are daily fare in bacteriology labs around the world.

But Chong Chen, a graduate student at the Chinese University of Hong Kong who was showing the movie at a 2015 physics meeting, highlighted a remarkable observation: As the colony grew more crowded, large groups of bacteria suddenly began moving nonrandomly, in a subtle but fascinating way. When the motions of thousands of bacteria were averaged, they traced out regular ellipses that were many times larger than the individual bacteria.

Hugues Chaté, a theoretical physicist at CEA Saclay in France, approached Chen after the session and said he had the theoretical tools to explain Chen’s strange results. The two teamed up, along with Chen’s adviser, Yilin Wu, and this February they published a paper inNature showing how seemingly uncoordinated motions of individual bacteria can add up to synchronized oscillations at large scales — a phenomenon never before reported in the scientific literature. They have since demonstrated the effect with other species and under different conditions. “This is something really robust and generic,” Chaté said. “It’s a surprising, spectacular phenomenon.”

The study is just one of the ways that researchers are exploring the strange collective behavior of bacteria. Bacterial colonies have been prodded into forming large-scale swirls and streams that seem to move like herds of animals. Researchers have organized bacteria into flowing crystals that resemble the liquid crystals in modern displays. And bacterial motion has even been used to power tiny machines.

Video: In a colony of E. coli cells, two silicone oil tracers exhibit synchronized loops.

The scientists are building a nascent field called “active matter,” in which simple mathematical rules governing interactions between individual units, each harnessing energy and moving on its own, can give rise to large-scale order. This approach has been wildly successful in explaining how water molecules crystallize into ice, and how atomic spins align to form magnets. Physicists are now pushing this idea to its limits in the vast, diverse microbial world. And they believe they have evidence that statistical physics could help explain some of bacteria’s most impressive — and nefarious — behaviors. . .

Continue reading.

This is another “bottom up” phenomenon, familiar from evolution and other emergent phenomenon.

Written by LeisureGuy

4 May 2017 at 12:09 pm

Posted in Math, Science

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