University of Texas at Austin

Monday, January 12, 2009

Physics in a petri dish

Harry Swinney

Harry Swinney

The latest research paper from Harry Swinney, a physics professor at The University of Texas at Austin, is on bacteria. The experiment, on which the paper in the Proceedings of the National Academy of Science is based, took place in a Petri dish of agar.

Physics and bacteria? That’s not a combination that goes together like McCoy and Cosby, fish and chips or public television and pledge drives.

But there is a connection, said Swinney, the Sid Richardson Foundation Regents Chair in the Physics Department.

The experiment determined that sibling colonies of bacteria battle against each other when the frontiers of their colonies come close to colliding. Swinney and Avraham Be’er, a post-doctoral student, conducted the experiment with University of Texas at Austin colleagues Hepeng Zhang, a research associate in physics, Ernest–Ludwig Florin, an assistant physics professor, and Shelley M. Payne, professor of molecular genetics and microbiology, and a Tel Aviv University physics professor, Eshel Ben-Jacob.

Henry Fountain, the Observatory columnist in the Science Times section of the New York Times, wrote about it in the Jan. 6, 2009 edition.

“Related colonies near one another on a bed of low-nutrient agar mutually inhibit growth by secreting an antibacterial compound that in high enough concentrations becomes lethal,” reported the Observatory item.

That is the colonies were growing just fine—until they got close to each other. Then they secreted an inhibitor that killed bacteria in the other colony.

So what’s that got to do with physics?

It has to do with patterns and the dynamics of pattern-forming systems, Swinney said. He is particularly interested in the similarities and differences of diverse systems.

“Bacteria colonies form fractal growth patterns quite similar to those we have studied in viscous fluids and in electrodeposition,” he said.

The study of bacterial patterns led to the study of the growth of competing colonies.

Furthermore, the project was very much in Swinney’s pattern of conducting tabletop experiments.

The first thing you read on this Web site sets out his experimental philosophy:

My research as a graduate student and all my research since then has involved tabletop, conceptually simple experiments. In this style of research a graduate student can design and build the experiment and collect and interpret the data.

A scientist can do a lot on a tabletop.

“In the past couple decades,” Swinney said, “we have studied Jupiter’s Great Red Spot, flowing sand, breaking glass and chemical spatial patterns, and in earlier years I studied the properties of filamentous viruses.”

Nor are Swinney’s experiments bound by disciplinary demarcations.

“I have collaborated closely with mathematicians, engineers, chemists, astronomers and biologists,” he said. “The boundaries between disciplines were mostly set in the 19th century and there is no reason that nature’s open questions must lie neatly within those boundaries.”

The goal, he said, is to “let nature speak.”

And in this experiment the bacteria spoke to each other in a deadly fashion.

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