May 8, 2013

Pioneer bacteria lay down trails that draw new recruits

UW Health Sciences and UW Medicine

bacteria form colonies

Northwestern University

Just as people take roads to gather in cities, some bacteria follow trails to congregate in colonies.

Bacteria may draw other bacteria to a site of infection by laying down trails of a “molecular glue” that lead free-swimming individuals to come together and organize into colonies.

In the study, researchers were looking at how a species of bacteria called Pseudomonas aeruginosa attach and move about on surfaces. P. aeruginosa is a common cause of serious, often difficult-to-treat infections.

One reason they are so difficult to treat is their ability to mass together and surround themselves with matrix of proteins, DNA and polysaccharides, called a biofilm, that protects them from antibiotics and the body’s immune attack.

The study was the result of a collaboration of researchers from the University of California, Los Angeles, the University of Washington in Seattle, and Northwestern University in Evanston, Illinois.

The findings were published May 8 in Nature in a paper titled, “Psl trails guide exploration and microcolony formation in Pseudomonas aeruginosa biofilms.”

Kun Zhao. from the UCLA Department of Bioengineering and Boo Shan Tseng from the UW Department of Microbiology are the paper’s lead authors. The senior authors are Gerald C. L. Wong, professor of bioengineering at the California Nanosystems Institute at UCLA;  Matthew R. Parsek,  UW  professor of microbiology, and Erik Luitjen, at Northwestern University.

In earlier studies, the researchers had noticed that when individual, free-swimming P. aeruginosa attached themselves to glass and began to crawl along the surface they left a trail of a polysaccharide called Psl.

“This was surprising because in the bacterial world this is somewhat unusual,” said Parsek,. “And it looked cool. But the question was whether it was biologically important.”

For this study, the researchers used a specially designed chamber that allowed them to watch how free-swimming P. aeruginosa attached to and moved about on a glass surface. They then used video microscopy to track and analyze the behavior the bacteria.

“Some of the bacteria remained fixed in position,” said Parsek. “But some moved around on the surface, apparently randomly but leaving a trail that influenced the surface behavior of other bacteria that encountered it.”

Once enough of the bacteria had gathered, about 50 or so, their behavior changed: they abandoned their wandering ways and began to organize into small structures called micro-colonies, the first step in biofilm formation.

If there are ways to inhibit the formation of these trails or block their effect, it may be possible to inhibit the formation of biofilms, Parsek said. This might help prevent infections or make them easier to treat.

The researchers are also interested to learn whether other bacterial species also take these polysaccharide trails as a signal to congregate. Pseudomonas infections often involve other bacterial species and this might explain how these polymicrobial infections get started.

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The UW portion of the study was supported by National Institutes of Health grants R01HL087920, R01AI077628, R01AI081983, R56AI061396 and National Science Foundation grant MCB0822405.

 

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