Thanks to a slime mould and the gene it donated, the nematode Pristionchus pacificus is able to make better use of its food. This is reported by a working group led by Ziduan Han from the Max Planck Institute for Biology in Tübingen. As the team reports in Molecular Biology and Evolution, the worm carries eight copies of a gene for the enzyme cellulase, which breaks down cellulose – the most important component of wood and other plant substances. This is unusual not only because of the rare case of gene transfer between two non-single-celled organisms, but also because the worm is not a herbivore at all. Nevertheless, the working group showed that the animal benefits from the gene transfer. As it turns out, the enzyme breaks down the biofilms that the worm feeds on – making nutrients more accessible.
It has been known for a while that the nematodes of the genus Pristionchus took over the gene for cellulase from a slime mold a few million years ago. But it has remained a mystery what Pristionchus pacificus does with the enzyme – the worm grazes microbial films on beetle shells. The molecule, on the other hand, breaks down plant matter, which the worm does not eat at all. Nevertheless, cellulase is so helpful for the worm that the gene for it doubled several times over time. As the team led by Han found in experiments with genetically modified worms, the animals with cellulase thrive much better than those in which the genes are switched off.
The explanation for the finding is that the food of the worm is virtually packaged. The microorganisms, of which the animal feeds, form biofilms - layers of mucus from networked biomolecules in which bacteria are protected from external influences. In some cases, the biofilms also consist of cellulose -like molecules, which are disassembled by the cellulase of the worm. As a result, the robust film is disintegrating, and the worm can gain more nutrients from the bacteria it contains thanks to the Gentransfer. In addition, the decomposed molecules of the biofilm provided energy, Han notes according to a press release from the institute. "It is to be handed in cellulase as if you can eat the pizza and the box," he says.
