The world of, and in, the worm So, rather than the monoxenic environment of the agar plate, it is rich habitats like a rotting apple that C. elegans’ chemosensory system has evolved to process. C. elegans lives in a complex ecosystem of bacteria, fungi, slime moulds, hexapod arthropods (adults and larvae), mites, isopods, millipedes, pulmonate molluscs, lumbricid earth worms and other nematode species exploiting this seasonal resource. C. elegans has a fully functioning immune system, with both anti-cellular (bacterial, fungal) and anti-viral arms intact. In the laboratory, in the absence of knowledge of natural pathogens, these systems have been challenged with exotic ones, such as the agents of human disease. C. elegans can be killed by many bacterial species, sometimes through direct toxic effect but also via interference with efficient processing of food [8]. In the laboratory one of the hallmarks of pathogenic interaction between a bacterium and C. elegans is the proliferation of bacteria within the gut. The species that do this avoid lysis in the nematodes’ pharyngeal grinder, and are resistant to digestion. Interestingly, Félix and Duveau [4] found many instances of apparently healthy nematodes with distended
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