Sunday, June 13, 2010

wormy new gut-ecosystem model


Video - live trichuris in the cecum.

The Scientist | A new class of organisms may be cutting in on the classic, co-evolutionary, immune system-boosting tango between mammals and the beneficial bacteria that inhabit their guts: parasitic worms.

Researchers at the University of Manchester in the United Kingdom report this week in Science that they have found that parasitic worms of the genus Trichuris -- inhabitants of many a mammal's large intestine -- are dependent upon common gut bacteria, such as E. coli, to reproduce inside their mammalian hosts. This means that the worms likely evolved alongside the bacteria that share their host and may play a more crucial role in building and modulating mammalian immune responses than previously expected.

"Having a low number of worms that don't cause disease may be effective in developing a robust and effective immune response," University of Manchester microbiologist Ian Roberts told The Scientist. "You end up with a kind of beneficial ecosystem."

Looking at a species of Trichuris that commonly infects mice, Roberts and his colleagues found that the worm's eggs would only hatch in the presence of bacterial cells, which clustered around tiny trap doors in the oblong egg capsules through which the worms would emerge. When bacteria were absent, hatching ceased.

This strategy makes sense for the worms, Roberts added, because their dispersal to different hosts depends upon a life spent in the nether regions of the digestive tract, during which they hatch out of eggs and lay more that are released in the host's feces. Trichuris worms don't hatch in stomachs or small intestines -- only in large intestines, where large numbers of bacteria also reside.

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