A novel bacterial pathogen, Microbacterium nematophilum, induces morphological change in the nematode C-elegans

The Dar (deformed anal region) phenotype, characterized by a distinctive sw ollen tail, was first detected in a variant strain of Caenorhabditis elegan s which appeared spontaneously in 1986 during routine genetic crosses [1,2] , Dar isolates were initially analysed as morphological mutants, but we rep ort here that two independent isolates carry an unusual bacterial infection different from those previously described [3], which is the cause of the o ar phenotype. The infectious agent is a new species of coryneform bacterium , named Microbacterium nematophilum n. sp., which fortuitously contaminated cultures of C. elegans. The bacteria adhere to the rectal and post anal cu ticle of susceptible nematodes, and induce substantial local swelling of th e underlying hypodermal tissue. The swelling leads to constipation and slow ed growth in the infected worms, but the infection is otherwise non lethal. Certain mutants of C. elegans with altered surface antigenicity are resist ant to infection. The induced deformation appears to be part of a survival strategy for the bacteria, as C. elegans are potentially their predators.