“Adhere today, here tomorrow” – how is exopolysaccharide production by Pseudomonas aeruginosa affected by high-flow shear conditions?

Biofilms provide physical, mechanical and chemical protection for microbes from their external environment, necessitating the use of harsh chemicals (such as sanitisers and antimicrobials) and abrasive cleaning (brushing or pigging) for their control. Biofilms have a broad impact upon the manufacturing of a wide range of fast-moving consumer goods, and biofilm contamination during their manufacture can lead to production interruption and significant economic costs to industry for cleaning and sanitisation. Biofilms formed by Pseudomonas aeruginosa (Ps. a.), a major contaminant of industrial processes, have yet to be studied in-depth with respect to the changes that occur in response to high-flow shear conditions from a combined physical and biological perspective.

The central aims of this work were to understand and elucidate the biological response of Ps. a. biofilms when grown under different, industrially-relevant fluid flow conditions; to characterise the mechanisms through which Ps. a. produces phenotypic responses, and how these in turn affect biofilm architecture. Two strains of Ps. a., PA01 and PA14, were used, known to differentially produce two exopolysaccharides (Psl and Pel respectively), integral components in the biofilm’s protective extracellular matrix (Colvin et al. 2012).

To investigate the effect of shear stress on biofilm formation, the CDC Bioreactor (CBR) was used to grow biofilms on polyethylene coupons under high or low shear conditions for 96 hours. At 24, 48, 72 and 96-hour timepoints, coupons containing biofilms were removed from the CBR and analysed by confocal laser scanning microscopy (CSLM) and biochemical assays.

Exopolysaccharide (EPS) production was quantified by CSLM image analysis in Fiji. In order to determine how EPS organisation effects wider biofilm architecture and individual structures within a maturing biofilm, Psl and Pel localisation and distribution throughout biofilms was assessed. Under low and high shear conditions, the architecture of PA01 and PA14 biofilms was compared to further identify similarities and differences in their phenotypic responses to shear stress.

We will present data that shows that Psl and Pel have distinct localisation patterns throughout PA01 and PA14 biofilms over our selected time course. PA01 and PA14 were shown to produce varying amounts of the exopolysaccharides Psl and Pel in mature biofilm structures (i.e. mushroom colonies) and throughout the entire biofilm population. Early adhesion, colony morphology and overall biofilm architecture was shown to be considerably affected by shear. Hydrodynamic conditions impose shear stress on Ps. a. biofilms, in turn affecting the structural components that make up their mature architecture.

Reference: Colvin, K.M., Irie, Y., and Tart, C.S. et al. (2012). The Pel and Psl polysaccharides provide Pseudomonas aeruginosa structural redundancy within the biofilm matrix. Environmental Microbiology, 14(8):1913-28.