Rheological variability of P. aeruginosa pellicles

A current trend in biofilm research uses changes in biofilm viscoelasticity to evaluate how biological mechanisms adapt to environment. However, it can be difficult to interpret results due to un-quantified variability in biofilm propertie, making comparison between different growth conditions, strains, mutant, or species nearly impossible. To interpret biofilm viscoelasticity requires understanding the statistical variance in biofilm mechanical properties.

In this work, 20 identically grown pellicles (biofilms formed at an air/water interface) composed of P. aeruginosa are characterized using an interfacial rheometer. The linear viscoelastic moduli of the biofilms are constantly tested over a 48 hour period, allowing pellicle formation to be captured. The repeated tests allow a quantitative evaluation of variability in biofilm mechanical properties. A range of greater than 1 order of magnitude and standard deviations of 100% are observed in the value of viscoelastic moduli. Onset of stages of formation are seen to vary by several hours. To our knowledge, this is the first such attempt to actually quantify such variability. Understanding the statistical variance among the experiments will lead to a better evaluation of biofilm formation in future studies.