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 earthworms and other nematode species exploiting this seasonal resource.
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 intestines full of bacteria and yeasts. Whether this is a nutritive (C. elegans
is deficient in sterol synthesis and must obtain sterols from food: this may be derived from yeasts) or a morbid interaction remains to be tested. However, fungal pathogens were detected, including some species that produce invasive spores, and others that make nematode-trapping rings and adhesive hyphal traps. As previously described by Félix and colleagues, many nematodes were infected with microsporidia [9
], and the first-ever nematode viruses were described from these orchards only last year [10
]. Killer bacteria were also isolated, including strains that can digest even the resistant cuticle of the nematodes.