Much remains to be discovered about the interactions of. Caenorhabditis elegans with the bacteria it encounters in the natural. world. One extensively studied pathogen for the genus Caenorhabditis, the. coryneform Microbacterium nematophilum, has been isolated repeatedly as a. contaminant in laboratory cultures, but so far it has not been found in the. wild. M. nematophilum attacks the worm by rectal infection and causes a. conspicuous tail swelling, akin to an inflammatory response.. Many worms in the population of a new C. elegans isolate, JU1088,. found in an aviary in Kakegawa, Japan, displayed rectal infection and a. swollen tail (Dar = Deformed anal region phenotype) similar to that caused. by M. nematophilum. The bacterium responsible was isolated in pure. culture and found to belong to a different genus of Microbacteriaceae,. called Leucobacter. 16S ribosomal RNA sequencing indicates that it is. distinct from other Leucobacter species so far described, so it is. provisionally termed Leucobacter n. sp. Japan, or LJ for short. The. finding of a natural population chronically infected with LJ shows that Dar. infections are a real hazard for C. elegans in the wild. A different. Leucobacter species, L. chromiireducens, has also been recently isolated. from infected C. elegans (Muir and Tan, 2007).. Numerous C. elegans mutants have been isolated with altered response. to M. nematophilum (Gravato-Nobre et al. 2005), being either resistant to. infection or defective in the swelling response (ca. 30 genes to date).. These have been tested for sensitivity to LJ, and fall into at least three. categories: many respond similarly to both M. nem and LJ, some are. resistant to M. nem and sensitive to LJ, and some are hypersensitive to LJ.. A different kind of worm/bacterial interaction has been discovered in. the form of a strain of Bacillus pumilus, which causes severe impairment to. the locomotion of wildtype C. elegans, apparently by surface adhesion. In. contrast, various mutants with abnormal cuticle and resistance to bacterial. surface infection, such as
srf-3 and
bus-4, are able to swim normally. through the sticky bacterial lawn. Another strain of B. pumilus, SAFR-032,. which has been fully sequenced as a consequence of its astrobiological. importance, fails to affect C. elegans movement. B. pumilus stickiness. provides a new and convenient assay for distinguishing between different. mutant alterations of the nematode surface.