Soft-matter mechanics in the initiation and robustness of bacterial biofilms
August 30, 2016 - 3:00pm to 4:00pm
IC Rm. 107
University of Texas at Austin
Biofilms are communities of microbes that are embedded in a self-produced matrix of polymer and proteins. Biofilms cause chronic, recalcitrant infections - even bacteria that are easily cleared by antibiotics and/or the immune system when they are in a free-swimming, so-called "planktonic" state become highly resistant to both antibiotics and the immune system when they are in a biofilm. We study biofilms grown from the bacterium Pseudomonas aeruginosa,
an opportunistic human pathogen that produces chronic biofilm infections in patients with cystic fibrosis, chronic obstructive pulmonary disease, and diabetes.
We find that bacteria sense that they are on a surface, and therefore change their gene expression to start making a biofilm, by sensing shear stress. Shear stress is mediated by sticky polymers that bind the bacteria to the surface, and varying the strength of polymermediated adhesion changes how well the bacteria can sense that they are on a surface. This suggests new ways to make surfaces that resist the development of biofilms by preventing bacteria from experiencing shear stress.
The same sticky polymers that adhere single-cell bacteria to surfaces are the major structural components of the mature biofilm matrix. P. aeruginosa biofilm matrices can contain up to three different polysaccharides. We find that these polysaccharides confer different mechanical properties to the biofilm through their binding with other protein and polymer components of the matrix. For decades-long infections in the lungs of cystic fibrosis patients, evolutionary changes in polysaccharide production result in changes in biofilm mechanics that are consistent with the idea that increased toughness and stiffness may help protect the biofilm against phagocytosis by immune cells.