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.

Figure 1

(A) Time course of paralysis of C. elegans by P. aeruginosa. Error bars show SDs of three independent trials. w.t., wild type. (B) Postures of paralyzed nematodes. Arrow indicates a hypercontracted nose.

Figure 2

(A) Amino acid sequence of EGL-9 as predicted by cDNA yk130h5. (B) Structure of egl-9 gene. Dark boxes indicate exons; arrows show locations of point mutations; the bar shows genomic DNA deleted in allele sa307. (C) Alignment of homologous regions of EGL-9 and rat SM-20 (GenBank accession no. U06713).

Figure 3

(A) Digital epifluorescence and Nomarski images of egl-9∷gfp expression in the pharyngeal muscles. Nuclear localization is incomplete, resulting in fluorescence of entire cells. The epifluorescence image has been deconvoluted with deltavision 2.1 software to eliminate light scattering from other focal planes. Fluorescence from several anterior ganglion neurons can also been seen. (B) Epifluorescence and Nomarski 35-mm images of egl-9∷gfp expression in body wall muscle. Arrows indicate muscle cell nuclei.