Lethal paralysis of Caenorhabditis elegans by Pseudomonas aeruginosa

Abstract

Identification of host factors that interact with pathogens is crucial to an understanding of infectious disease, but direct screening for host mutations to aid in this task is not feasible in mammals. The nematode Caenorhabditis elegans is a genetically tractable alternative for investigating the pathogenic bacterium Pseudomonas aeruginosa. A P. aeruginosa toxin, produced at high cell density under control of the quorum-sensing regulators LasR and RhlR, rapidly and lethally paralyzes C. elegans. Loss-of-function mutations in C. elegans egl-9, a gene required for normal egg laying, confer strong resistance to the paralysis. Thus, activation of EGL-9 or of a pathway that includes it may lead to the paralysis. The molecular identity of egl-9 was determined by transformation rescue and DNA sequencing. A mammalian homologue of EGL-9 is expressed in tissues in which exposure to P. aeruginosa could have clinical effects. T he use of genetic strategies to identify host factors with which pathogens interact has been limited by the fact that traditional disease model hosts, live mammals or their cultured cells, are not amenable to facile genetic analysis. Invertebrate models, such as the nematode Caenorhabditis elegans and the fruit fly Drosophila melanogaster, offer sophisticated genetic methods but have rarely been used to study infectious disease. Complete sequencing of the genome of C. elegans indicated that at least 36% of the 19,000 predicted proteins have matches in humans (1). Thus, despite the enormous evolutionary distance between humans and nematodes, C. elegans may be a valid model for studies of numerous disease processes.Pseudomonas aeruginosa is an opportunistic pathogen that infects patients compromised by illness, injury, or inborn genetic defect (2, 3). Hospital-acquired P. aeruginosa pneumonias and septicemias are frequently lethal, and the bacteria infect the lungs of the majority of patients with cystic fibrosis. P. aeruginosa secretes numerous protein virulence factors, including ADP ribosylating enzymes, proteases, and phospholipases, as well as small molecules that include phenazines, rhamnolipid, and cyanide. Production of some of these factors is controlled by one or both of two quorum-sensing systems, LasI͞R and RhlI͞R, which tie gene expression to high cell density (4).Recently, Ausubel and colleagues (5-7) described a model for P. aeruginosa pathogenesis that uses C. elegans. Depending on the experimental conditions, strain PA14 kills the nematodes over a period of days (slow killing) or hours (fast killing). The fast killing is mediated by the production of phenazine compounds, which may act through the generation of active oxygen species.Using a different strain of P. aeruginosa (8), we have identified a third mode by which this species can kill C. elegans. The lethal effect is associated with a rapid neuromuscular paralysis and is caused by the action of one or more diffusible factors whose production requires the Las and Rhl quorum-sensing systems. C. elegans strains carrying loss-of-func...

Programmed cell death mediated by ced-3 and ced-4 protects Caenorhabditis elegans from Salmonella typhimurium -mediated killing

“…In addition, C. elegans mutants that are either more susceptible or more resistant to bacterial killing can be readily identified (7,8). These facts make C. elegans an attractive host for dissecting the molecular basis of bacterial pathogenesis.…”

“…5 and 8). P. aeruginosa strain PAO1 grown on brain-heart infusion medium kills by a third mechanism involving the generation of one or more neurotoxins (7). A variety of S. enterica serovars, including S. typhimurium, grown on NG medium, kill C. elegans over the course of several days by a mechanism that involves the establishment of a persistent infection in the C. elegans intestine (1).…”

“…S everal human pathogens, including Pseudomonas aeruginosa, Salmonella typhimurium, Serratia marcescens, and Burkholderia pseudomallei, kill the nematode Caenorhabditis elegans when supplied as a food source, and a variety of bacterial virulence factors have been shown to play a role in both nematode and mammalian pathogenesis (1-6). In addition, C. elegans mutants that are either more susceptible or more resistant to bacterial killing can be readily identified (7,8). These facts make C. elegans an attractive host for dissecting the molecular basis of bacterial pathogenesis.…”

A Caenorhabditis elegans model of Yersinia infection: biofilm formation on a biotic surface

“…These include a variety of plant and animal pathogens such as Erwinia chrysanthemi, Agrobacterium tumefaciens, Shewanella frigidimarina, Photorhabdus luminescens, Xenorhabdus nematophilus (Couillault & Ewbank, 2002) and 'Microbacterium nematophilum' (Hodgkin et al, 2000). They also include bacteria pathogenic to humans, including the Gramnegative bacteria Pseudomonas aeruginosa, which kills the worm by one of three mechanisms -fast, slow or neurotoxin-mediated (Tan et al, 1999;Darby et al, 1999), Burkholderia pseudomallei, which kills via a neuromuscular endotoxin (O'Quinn et al, 2001), and Serratia marcescens, which also kills via a (different) toxin (Kurz & Ewbank, 2000); and the Gram-positive bacteria Enterococcus faecalis, Streptococcus pneumoniae and Staphylococcus aureus (Garsin et al, 2001).…”

srf-3, a Mutant of Caenorhabditis elegans, Resistant to Bacterial Infection and to Biofilm Binding, Is Deficient in Glycoconjugates

“…Among the latter are plant and animal pathogens such as Erwinia chrysantheimi, Agrobacterium tumefaciens, Shewanella frigidimarina, Photorhabdus luminescens, Xenorhabdus nematophilus (1), Yersinia pseudotuberculosis (2,3), and Mycobacterium nematophilum (4). Human pathogens can also infect C. elegans, including Gram-negatives, such as Pseudomonas aeruginosa (5), Burkholderia pseudomallei (6), Serratia marcesens (7,8), and Yersinia pestis (2), and gram positives, such as Streptococcus pneumoniae, Enterococcus faecalis, and Staphylococcus aureus (9).…”