Trichoplax, together with sponges and jellyfish, belongs to one of the most basal lineages of the animal kingdom. Until the 70ies, it was not even clear if Trichoplax is a proper, fully-grown animal or just the juvenile stage of a jellyfish. Only about a half a millimetre in diameter, these animals lack a mouth, gut and any other organs, and are made up of only six different kinds of cells. Its simplicity makes it a popular model organism for biologists.
Scientists from the Max Planck Institute for Marine Microbiology in Bremen, Germany, the University of Hawaii and North Carolina State University have now discovered that Trichoplax is not as simple as it looks. It lives in a remarkably sophisticated symbiosis with highly unusual bacteria.
Observation - Bacteria - Trichoplax - Years - Zoologist
The first observation of bacteria in Trichoplax was nearly 50 years ago by the German zoologist Karl Grell. But no one has really taken a closer look since then. An international group of scientists around Harald Gruber-Vodicka, Niko Leisch and Nicole Dubilier from the Max Planck Institute for Marine Microbiology, and Michael Hadfield from the University of Hawaii have now investigated the bacterial tenants of Trichoplax by sequencing their genomes and using high-resolution microscopy to see where they live. "Despite being so simple, Trichoplax harbors two very different and highly unusual bacterial symbionts in its cells," says Gruber-Vodicka. "Both symbionts are very picky -- or cell-specific, as we call it. Each symbiont lives in only one type of host cell."
One symbiont, named Grellia after the zoologist Karl Grell, lives inside the endoplasmic reticulum (ER) of Trichoplax, and is the first symbiont known to permanently live in an animal's ER. The ER plays a central role in protein and membrane production. Proving that Grellia is truly in the ER was challenging. "We reconstructed a detailed three-dimensional model of the...
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