R-045. Experimental Evolution of Burkholderia cenocepacia Planktonic and Biofilm Populations: Identifying the Effects of Niche Selection

S. R. Poltak, V. S. Cooper;
Univ. of New Hampshire, Durham, NH.

Background: The ability for bacteria to infect and persist within a host has been linked to the organism’s ability to produce biofilms, especially in the lungs of those who suffer from cystic fibrosis (CF). Burkholderia cenocepacia is a potentially lethal opportunistic pathogen that is highly resistant to antibiotics and thrives within the CF lung. We hypothesized that selection in a biofilm favors shifts in life history that oppose efficient planktonic growth, and conversely that planktonic selection may oppose biofilm formation. Methods: To test this hypothesis, we have evolved six B. cenocepacia HI2424 biofilm populations and six planktonic populations via daily serial for 1000 generations in galactose minimal media. Biofilm populations were propagated on 6mm polystyrene beads and forced to colonize a new bead every 24 hours, while planktonic populations were propagated by daily 1:100 dilution. Fitness in each environment was assessed by direct competition with the ancestor. Results: After 1000 generations, all populations adapted significantly to their treatment environment but were less fit in the alternative environment, supporting our primary hypothesis. We also observed significant fitness variance among clones within biofilm-evolved populations owing to the repeated evolution of three distinct morphotypes. No heterogeneity was observed within planktonic populations. The three morphotype groups varied widely in their biofilm production and were themselves heterogeneous, suggesting multiple pathways to their evolution. Conclusion: Selection of B. cenocepacia under conditions favoring biofilms repeatedly produced three distinct morphotypes that varied in both fitness and biofilm production. These results imply that morphotype evolution and fitness variance may be a product of cooperation, frequency dependence, and/or metabolite crossfeeding between the biofilm morphotypes.