Genomic analysis reveals that Pseudomonas aeruginosa virulence is combinatorial.
BACKGROUND
Pseudomonas aeruginosa is a ubiquitous environmental bacterium and an important opportunistic human pathogen. Generally, the acquisition of genes in the form of pathogenicity islands distinguishes pathogenic isolates from nonpathogens. We therefore sequenced a highly virulent strain of P. aeruginosa, PA14, and compared it with a previously sequenced (and less pathogenic) strain, PAO1, to identify novel virulence genes.


RESULTS
The PA14 and PAO1 genomes are remarkably similar, although PA14 has a slightly larger genome (6.5 megabses [Mb]) than does PAO1 (6.3 Mb). We identified 58 PA14 gene clusters that are absent in PAO1 to determine which of these genes, if any, contribute to its enhanced virulence in a Caenorhabditis elegans pathogenicity model. First, we tested 18 additional diverse strains in the C. elegans model and observed a wide range of pathogenic potential; however, genotyping these strains using a custom microarray showed that the presence of PA14 genes that are absent in PAO1 did not correlate with the virulence of these strains. Second, we utilized a full-genome nonredundant mutant library of PA14 to identify five genes (absent in PAO1) required for C. elegans killing. Surprisingly, although these five genes are present in many other P. aeruginosa strains, they do not correlate with virulence in C. elegans.


CONCLUSIONS
Genes required for pathogenicity in one strain of P. aeruginosa are neither required for nor predictive of virulence in other strains. We therefore propose that virulence in this organism is both multifactorial and combinatorial, the result of a pool of pathogenicity-related genes that interact in various combinations in different genetic backgrounds.
Lee
Daniel G
DG
Department of Molecular Biology, Massachusetts General Hospital, Cambridge Street, Boston, Massachusetts 02114, USA.
Urbach
Jonathan M
JM
Wu
Gang
G
Liberati
Nicole T
NT
Feinbaum
Rhonda L
RL
Miyata
Sachiko
S
Diggins
Lenard T
LT
He
Jianxin
J
Saucier
Maude
M
Déziel
Eric
E
Friedman
Lisa
L
Li
Li
L
Grills
George
G
Montgomery
Kate
K
Kucherlapati
Raju
R
Rahme
Laurence G
LG
Ausubel
Frederick M
FM
D001483:Base Sequence; D020650:Combinatorial Chemistry Techniques / Q000379:methods; D017931:DNA Primers; D004269:DNA, Bacterial / Q000235:genetics; D016680:Genome, Bacterial; D023281:Genomics; D020411:Oligonucleotide Array Sequence Analysis; D016133:Polymerase Chain Reaction; D011549:Pseudomonas / Q000235:genetics* / Q000472:pathogenicity*; D017422:Sequence Analysis, DNA; D014774:Virulence / Q000235:genetics*
D017931:DNA Primers; D004269:DNA, Bacterial