Contribution of CdiA to Pseudomonas aeruginosa pathobiology

Project Summary/Abstract
Pseudomonas aeruginosa is a leading cause of healthcare-acquired infections worldwide. Many globally-
distributed high-risk strains are emerging due to an increase in antibiotic resistance and acquisition of novel
virulence traits. With diminishing treatment options for many of these severe P. aeruginosa infections, studies
aimed at uncovering the virulence strategies used by these aggressive clinical strains should help to identify new
targets for therapeutic intervention. Our research program aims to elucidate virulence strategies that enhance
the pathogenicity of P. aeruginosa. We recently employed a comparative genomics approach to interrogate the
accessory genomes of 100 clinical isolates for potential factors that augment the virulence of P. aeruginosa. By
comparing virulence in a mouse infection model with the presence or absence of genes in the accessory genome,
we identified several virulence determinants enriched among highly virulent P. aeruginosa strains that were
absent from less virulent strains. From this work we identified an accessory virulence factor that spanned a
portion of two genes encoding products involved in contact-dependent growth inhibition (CDI). CDI is one type
of competitive mechanism microorganisms use to antagonize their immediate neighbors by delivering protein
toxins directly into targeted cells. This antagonism is executed by CdiA, a large multidomain exoprotein that sits
at the surface of an attacking cell and delivers a self-contained toxin domain into the targeted cell. The
importance of this proposal stems from our discovery that: (i) CdiA contains a toxin domain that has tRNAse
activity against prokaryotic and eukaryotic substrates, (ii) mutations that abrogate the in vitro tRNAse activity
attenuate both CDI and virulence in mice, (iii) the CdiA-toxin domain has cytopathic effects on eukaryotic cells
dependent upon its tRNase activity. To our knowledge this dule role for CdiA in both interbacterial completion
and virulence within a mammalian host has not yet been investigated for P. aeruginosa. From this preliminary
work we hypothesize that P. aeruginosa can utilize CdiA to intoxicate host cells for overcoming barriers to
infection. Our proposal seeks to answer a number of outstanding questions at the molecular (Aim 1), cellular
(Aim 2), and organismal (Aim 3) level. Successful completion of these aims will provide detailed insight into how
CdiA contributes to P. aeruginosa pathobiology.

Grant Number: 5R01AI163119-05
NIH Institute/Center: NIH
Principal Investigator: Jonathan Allen