Research Could Lead to Development of "Cancer Traps"

"Physicists in the US are the first to show that E. coli bacteria can work together to swim through a tiny ratchet that would normally block individual organisms."

Researchers at Princeton University constructed an obstacle course, if you will, for E. coli to navigate through. The course was about 13mm long and 100microns wide, and it was divided into 85 channels separated by "ratcheted" walls. As the illustration in the link suggests, the ratchets were like funnels which allowed the bacteria to cross in one direction but blocked them from traveling in the other direction.

A population of E. coli was placed in one end of the chamber in such a fashion that it would be blocked from reaching the other end; the ratchets were oriented against them. When fewer than 200 of the bacteria were in the first channel, none of them could make their way through the ratchet to reach the next channel. Their movement forward was successfully blocked by the wall.

However, when the number of bacterium in the initial chamber increased to about 1000, the majority of the population was about to make its way to the end of the entire course within about two hours.

To understand this, the physicists had to understand the mechanism which allows the micro-organisms to move. E. coli utilize chemicals in their immediate environment to move their flagella, a process known as chemotaxis (http://en.wikipedia.org/wiki/Chemotaxis). Basically, the organisms consume certain chemicals in order to mechanically propel themselves forward.

When a mass amount of E. coli gets together, they consume relatively massive amounts of this chemical. This creates a concentration gradient of said chemical and therefore has a compounding effect on their movement, giving them an extra "boost" along the chemical gradient. So when the population of organisms is large, they are able to move through barriers that they normally wouldn't be able to move through individually (in this example, the reverse-bias ratchets). This is exactly the collective behavior predicted by the Keller-Segel equations, which were formulated many many moons ago.

This research could lead to the development of "cancer traps", which would be placed inside the body in order to prevent the spreading of cancerous cells. The idea is that instead of cancerous cells being able to freely travel throughout the body, the ratchets could be placed in such a fashion that would require the cells to achieve massive densities before escaping their immediate surroundings; densities that would most likely not be achievable. Another implication is the better overall understanding of how E. coli traverses within our large intestine.

-Trevor Lancon

http://physicsworld.com/cws/article/news/42541