Pseudomonas aeruginosa PAO1 Kills Caenorhabditis elegans by Cyanide Poisoning

Abstract

In this report we describe experiments to investigate a simple virulence model in which Pseudomonas aeruginosa PAO1 rapidly paralyzes and kills the nematode Caenorhabditis elegans. Our results imply that hydrogen cyanide is the sole or primary toxic factor produced by P. aeruginosa that is responsible for killing of the nematode. Four lines of evidence support this conclusion. First, a transposon insertion mutation in a gene encoding a subunit of hydrogen cyanide synthase (hcnC) eliminated nematode killing. Second, the 17 avirulent mutants examined all exhibited reduced cyanide synthesis, and the residual production levels correlated with killing efficiency. Third, exposure to exogenous cyanide alone at levels comparable to the level produced by PAO1 killed nematodes with kinetics similar to those observed with bacteria. The killing was not enhanced if hcnC mutant bacteria were present during cyanide exposure. And fourth, a nematode mutant (egl-9) resistant to P. aeruginosa was also resistant to killing by exogenous cyanide in the absence of bacteria. A model for nematode killing based on inhibition of mitochondrial cytochrome oxidase is presented. The action of cyanide helps account for the unusually broad host range of virulence of P. aeruginosa and may contribute to the pathogenesis in opportunistic human infections due to the bacterium.Pseudomonas aeruginosa is a ubiquitous gram-negative bacterium that is virulent towards a wide range of organisms, including bacteria, plants, nematodes, insects, and mammals (5,9,17,19,35,36,41,48,49,62). In humans, P. aeruginosa chronically infects the lungs of most cystic fibrosis patients, causes serious infections of burn wounds and eye lesions, and causes systemic infections of immunocompromised individuals (21,29,33,39). The bacterium's pathogenic versatility is reflected in its large arsenal of secreted and surface-associated virulence factors and in the complexity of the regulatory circuitry with which it controls these factors. Among the specific virulence factors that it produces are adhesins, such as pili and filamentous hemagglutinin (14, 39); protein toxins, such as phospholipase, proteases, and ADP-ribosylating enzymes (39, 64); and small-molecule poisons, such as phenazines, rhamnolipid biosurfactant, and cyanide (4,8,44). Additionally, the genome of P. aeruginosa boasts the highest proportion of predicted regulatory genes of any of the bacterial genomes sequenced to date (61), which is indicative of the bacterium's remarkable ability to adapt and thrive in numerous pathogenic and nonpathogenic environments.Several model systems for Pseudomonas pathogenesis have been developed recently, and numerous genes required for virulence towards model hosts are also required for virulence towards mammals. For example, mutants of P. aeruginosa PA-14 exhibiting reduced virulence towards Arabidopsis or Caenorhabditis elegans also exhibit reduced virulence in a burned-mouse infection model (49,50,62). In addition, a putative Pseudomonas signal transduction gene cluster requi...

Complete genome sequence of the entomopathogenic and metabolically versatile soil bacterium Pseudomonas entomophila

“…5). PSEEN5520-PSEEN5522 are responsible for hydrogen cyanide production that is involved in Caenorhabditis elegans killing by P. aeruginosa 22 and in the suppression of soil-borne plant pathogens by certain Pseudomonas species 23 . The genome of P. entomophila contains four clusters of genes predicted to encode three different lipopeptides and a polyketide ( Table 2 and Supplementary Fig.…”

Bacterial cyanogenesis occurs in the cystic fibrosis lung

“…In CF airways, P. aeruginosa is thought to grow in anaerobic/reduced oxygen pockets situated within thickened and tenacious mucus plugs that occlude small airways [3,4]. This environment may be suitable for cyanide production by P. aeruginosa [5][6][7]. However, to date, it is not known whether bacteria are residing in strictly anaerobic or microaerobic pockets within the CF lung.…”

Acyl-homoserine lactone-dependent eavesdropping promotes competition in a laboratory co-culture model

“…One commonly occurring example is antimicrobials. Quorum-controlled antimicrobials have been described in many saprophytic Proteobacteria including Erwinia carotovora (Bainton et al, 1992), Pseudomonas aeruginosa (Kownatzki et al, 1987;Bainton et al, 1992;Gallagher and Manoil, 2001;Ran et al, 2003;Schuster and Greenberg, 2006), Burkholderia thailandensis (Bt) and Chromobacterium violaceum (Cv) (Latifi et al, 1995;McClean et al, 1997). Although some groups have proposed that antimicrobial activity of secondary metabolites is a side effect and the primary function of these compounds is as signals (Davies et al, 2006;Yim et al, 2007), the classic view is that they are used for competition with other strains or species in multi-species environments.…”