by Manuel Sánchez
When we highlight the importance of viruses in ecosystems, we usually assume that all living things, multi- or unicellular, can be infected by at least one kind of virus. This is not a far-fetched assumption, but one that until now has had to endure some notable exceptions. Viruses had not been found in certain groups of living organisms, notably the nematodes, the group that includes the model organism Caenorhabditis elegans.
This era is officially over now, as a couple of viruses have been described that infect these worms. In an article in PLOS Biology, the authors report that they have isolated and characterized viral agents. And they did it in the old-school way. Briefly, take a handful of worms, grind them up, filter the extract through a 0.2 µ filter, inject uninfected worms with this filtrate, and look for pathology. Marianne Felix, the first author, tried this and noticed that the worms got sick and could not be cured with antibiotics.
These new viruses damage the worms’ intestinal cells. They are a new taxon of single stranded RNA viruses related to the Nodovirus group. One that infects C. elegans specifically has been called the Orsay virus. Another one that infects C. briggsae is being called the Santeuil virus. The investigators found that one way the worms defend themselves is via RNA interference
Infected C. briggsae intestinal cells (Nomarski imaging). A normal cell is shown in B. Source.
Electron micrographs of intestinal cells of C. elegans. (G) uninfected), (H) infected. IF refers to
intermediate filaments, which become disorganized during infection. On the right of (H) are
putative virus particles seen at higher magnification (arrow heads). Source.
This is an important discovery. C. elegans is one of the principal model organisms for animals. Its development is known cell by cell, so one can correlate the infection with the stage in development. This is also a model for studying co-evolution between host and parasite and, of course, the response of the innate immune system to viral infections.