Scientists at the Max Planck Institute for Developmental Biology, together with American colleagues, have decoded the genome of the Pristionchus pacificus nematode, thereby gaining insight into the evolution of parasitism. In their work, which has been published in the latest issue of Nature Genetics, the scientists from Professor Ralf J. Sommer's department in Tübingen, Germany, have shown that the genome of the nematode consists of a surprisingly large number of genes, some of which have unexpected functions. These include a number of genes that are helpful in breaking down harmful substances and for survival in a strange habitat: the Pristionchus uses beetles as a hideout and as means of transport, and feeds on the fungi and bacteria that spread out on their carcasses once they have died. It thus provides the clue to understanding the complex interactions between host and parasite.
When they move from the land to the beetle, the nematodes' habitat changes dramatically. The nematodes have to protect themselves against toxic substances in their host, for example. The methods they employ to cope with the conditions in the beetle are worthy of closer attention, as this life form can possibly be regarded as the precursor to real parasites. At least, this is what researchers have suspected for a long time.The sequencing of the genome of Pristionchus pacificus has now confirmed this suspicion: the genome, consisting of around 170 megabases, contains more than 23,500 protein-coding genes. By comparison, the model organism of Caenorhabditis elegans and the human parasite Brugia malayi (whose genome was sequenced in 2007) only have about 20,000 or 12,000 protein-coding genes, respectively. "The increase in Pristionchus is partly attributable to gene duplications," explained Ralf Sommer. "These include a number of genes that could be helpful for breaking down harmful substances and for survival in the complex beetle ecosystem."Surprisingly, the Pristionchus genome also has a number of genes that are not known in Caenorhabditis elegans, although they have been found in plant parasites. Genes for cellulases - enzymes that are required to break down the cell walls of plants and microorganisms - have aroused particular interest among scientists. "The really exciting questions are still to come", said Sommer. "Using the sequence data, we can test how Pristionchus has adapted to its specific habitat. And this will undoubtedly give us new insight into the evolution of parasitism."Original publication:Dieterich, C., Clifton, S. W., Schuster, L., Chinwalla, A., Delehaunty, K., Dinkelacker, I., Fulton, L., Fulton, R., Godfrey, J., Minx, P., Mitreva, M., Roeseler, W., Tian, H., Witte, H., Yang, S.-P., Wilson, R. K. & Sommer R. J. (2008): The Pristionchus pacificus genome provides a unique perspective on nematode lifestile and parasitism. Nature Genetics, Advance Online Publication, September 21, 2008, doi:10.1038/ng.227.