The roles of mucD and alginate in the virulence of Pseudomonas aeruginosa in plants, nematodes and mice

We are exploiting the broad host range of the human opportunistic pathogen Pseudomonas aeruginosa strain PA14 to elucidate the molecular basis of bact erial virulence in plants, nematodes, insects and mice. In this report, we characterize the role that two PA14 gene products, MucD and AlgD, play in v irulence. MucD is orthologous to the Escherichia coli periplasmic protease and chaperone DegP. DegP homologues are known virulence factors that play a protective role in stress responses in various species. AlgD is an enzyme involved in the biosynthesis of the exopolysaccharide alginate, which is hy perinduced in mucD mutants. A PA14 mucD mutant was significantly impaired i n its ability to cause disease in Arabidopsis thaliana and mice and to kill the nematode Caenorhabditis elegans. Moreover, MucD was found to be requir ed for the production of an extracellular toxin involved in C. elegans kill ing. In contrast, a PA14 algD mutant was not impaired in virulence in plant s, nematodes or mice. A mucDalgD double mutant had the same phenotype as th e mucD single mutant in the plant and nematode pathogenesis models. However , the mucDalgD double mutant was synergistically reduced in virulence in mi ce, suggesting that alginate can partially compensate for the loss of MucD function in mouse pathogenesis.