THE ROLE OF SAWR IN REGULATING VIRULENCE AND BIOFILM FORMATION IN PSEUDOMONAS AERUGINOSA

Recent studies have shown that PA3133 (sawR), a probable transcription factor of Pseudomonas aeruginosa, is over-expressed in response to Surface Acoustic Waves (SAW). SAW is known to disrupt P. aeruginosa biofilm formation and antibiotic resistance. In this study we attempt to uncover the regulatory role of sawR in the bioacoustic response of P. aeruginosa.

A flow cell system was utilized to demonstrate that the biofilm of the sawR overexpressing strain is highly sensitive to antibiotic treatment and forms less biomass when compared to the wild type (WT) strain, mirroring the effects of SAW exposure on the WT.

In order to examine the genetic effects of sawR, a microarray was performed in which gene expression levels of the sawR overexpressing strain were compared to that of the WT. sawR showed a significant impact on gene expression pattern, where several virulence-associated genes were down-regulated in the sawR overexpressing strain, while specific metabolic genes were up-regulated. hmgA is a metabolic gene that is down-regulated in the sawR overexpressing strain. It is known that in the absence of hmgA, strains hyper-produce a brown pigment called pyomelanin, which is also produced by the sawR overexpressing strain.

The decreased expression of multiple virulence factors in the sawR overexpressing strain led us to examine whether sawR, when overexpressed, can reduce the virulence of P. aeruginosa. We used a HeLa cytotoxicity assay in which cytotoxic ability of the sawR overexpressing strain was compared to the WT and found that it decreased by approximately 50%.

Taken together, our data suggests that sawR plays a central role in mediating the response to SAW and key phenotypes such as biofilm formation, antibiotic resistance and pigment production.