Bacterial biofilms adjust their growth and toughness in response to physical stressors in the environment

Bacterial biofilms adjust their growth and toughness in response to physical stressors in the environment
Vernita Gordon, Dept. of Physics, University of Texas, Austin
Date and time: Thu, Feb 11, 2016 - 11:30am
Refreshments at 11:15am
Location: LGRT 1033
Category: Condensed Matter Seminar
Abstract:
In most natural settings, most bacteria are found in spatially-structured, pluralistic communities called "biofilms". The spatial structure of these communities governs interactions within and between species, and with the environment. Although it is widely recognized that the spatial arrangement of cells is important to the biology of biofilms, very few details are known. Here, we combine experiments, analytical modeling, and simulations to examine a case in which cooperative and competitive inter-bacterial interactions impact growth fitness. We find that the relative growth fitness of large, multicellular aggregates, compared with single cells, depends on the density of competition, which is set by the concentration of single cells. Biofilm bacteria have spatial structure because they are embedded in a mechanically-cohesive matrix scaffolded by extracellular polysaccharides (EPS). A single species of bacteria can produce more than one type of EPS; the reason(s) for this apparent redundancy are not well-understood, and the idea that different types of EPS could serve qualitatively different roles in biofilm mechanics is almost entirely unexplored. P. aeruginosa is an opportunistic human pathogen produces chronic, and ultimately fatal, biofilm infections in the lungs of patients with cystic fibrosis. Here, we show that evolutionary changes in the polymer production by different infecting sub-populations can result in qualitatively different types of changes in the mechanical toughness, stiffness, and yielding of the biofilm. We compare biofilm stiffness with the stresses exerted by neutrophils (phagocytic immune cells) during phagocytosis, and infer that the mechanical changes we measure for different patterns of polymer production may impinge on the biofilm infections’ resistance to clearance by the immune system.