The research appears in a recent issue of the journal PLoS Pathogens, published by the Public Library of Science.
Wozniak and colleagues had singled out Psl as the likely culprit in Pseudomonas biofilm creation a few years ago, but weren't certain about how it worked until this new series of experiments allowed them to view the entire matrix and biofilm development process.
The researchers are the first to note that the actual shape of Psl resembles a helix, a ladder-like structure, which stabilizes cell-to-cell interaction critical to the formation of a biofilm. Wozniak's group also observed that free-floating DNA, with its double-helix shape, exists within the Pseudomonas biofilm, offering additional web-like structural support to the mass of cells.
"The extracellular DNA works like another matrix. It's a long polymer that attracts all the bacteria together," said Luyan Ma, lead author of the study and a research scientist in Ohio State's Center for Microbial Interface Biology (CMIB).
The biofilm eventually grows into a three-dimensional mushroom-shaped mass. And then, in a programmed series of events, the biofilm initiates a process to create another microcolony of cells.
"At some point, there is either a nutritional or physiological cue that says, 'this is no longer advantageous and we need to start this process over again'," said Wozniak, also an investigator in CMIB.
As part of this process, some bacterial cells in the biofilm kill themselves to create a cavity from which seed cells can be released to begin the formation of a new mass. This kind of programmed cell death, called apoptosis, is typical of higher organisms, but has rarely been seen in bacteria, Wozniak said.
The researchers believe this cell death disrupts the matrix holding the existing biofilm together, releasing Psl and a host of nutrients and enzymes that support new "swimming" cells that move out of the biofilm t
|Contact: Daniel Wozniak|
Ohio State University