Elucidating the contribution of the Pseudomonas aeruginosa CPX system in biofilm formation

An investigation of Pseudomonas aeruginosa attachment to a diverse range of polymers in a high-throughput microarray format resulted in the discovery of novel biofilm-resistant and biofilm-stimulating materials. These findings raised questions about the nature of the surface interactions involved and in particular the sensory mechanisms use by P. aeruginosa to distinguish between different surface chemistries. To further investigate this, Tn5 mutants of the P. aeruginosa PAO1 Washington sub-line were tested for biofilm formation on the polymer microarrays. This revealed that a Tn5::cpxR mutant had a significant difference in biofilm formation when compared with PAO1-W. In Escherichia coli cpxR forms an operon with cpxA and cpxP. Together they form the CPX two-component signalling system controlling biofilm formation in response to cell envelope stress. To further characterise the P. aeruginosa cpxsystem, ΔcpxR,ΔcpxP and ΔcpxA deletion mutants were constructed. No significant differences were observed in their growth or in the swimming, swarming or twitch motility phenotypes normally required for surface colonization. Unlike E. coli the PAO1-W ΔcpxAmutant was able to invade lung epithelial cells and did not display increased sensitivity to antibiotics. However, the ΔcpxRmutant showed increased biofilm formation on glass and eDNA secretion in both biofilm and liquid modes of growth. This work highlights the relationship between biofilm formation and the CPX system in P. aeruginosa . However, further assays need to be conducted in order to understand the sensory mechanism(s) involved in surface sensing via the CPX system.