![Choanoflagellates are a class of free-living unicellular eukaryotes capable of assembling into multicellular clusters; the formation of such colonies is thought to have played a […]](/wp-content/uploads/2011/10/News-image-01-620x300.jpg "Colonies may have led to the evolution of multicellular organisms")
Choanoflagellates are a class of free-living unicellular eukaryotes capable of assembling into multicellular clusters; the formation of such colonies is thought to have played a role in the evolution of multicellular organisms. The choanoflagettes are therefore considered to be the closest living relatives of animals. The species Salpingoeca rosetta has been observed to form rosette-shaped colonies in certain conditions. Since choanoflagellates prey on bacteria, it has been proposed that rosette colony formation enables Salpingoeca rosetta to capture bacteria more effectively.
Choanoflagellates are constituents of the ocean’s plankton community and are characterised by a microvilli-coated and egg-shaped cell body possessing a flagellum for movement through an aqueous environment. During the genome sequencing of the choanoflagellate species Monosiga brevicollis an accidental discovery was made explaining the mechanism of colony formation. A medium containing the Monosiga brevicollis was exposed to antibiotics to destroy bacteria that would interfere with DNA sequencing. When certain antibiotic cocktails were used, colony formation was inhibited. This phenomenon could be explained by the ability of the bacterial species Algoriphagus machipongonensis to induce colony formation only when present as a dominant species in the medium. A type of sulfonolipid (components of bacterial membranes with a role in cell signalling) called RIF-1 was identified as the actuator of colony formation. The mechanism of colony formation is extremely sensitive to the presence of the RIF-1, which can be detected in tiny quantities.
The abundance of bacteria in the choanoflagellates’ marine habitat may explain how ancestors of the animal kingdom first evolved; the choano progenitor to animals was thought to have existed over 650 million years ago. Further studies of choanoflagellate colony formation may shed light onto the evolutionary processes that produced multicellular organisms.
