Scientists have found a new species of Choanoflagellate. This close relative of animals forms sheets of cells that 'flip' inside-out in response to light, alternating between a cup-shaped feeding form and a ball-like swimming form. The organism could offer clues about animals' early evolution.
Choanoflagellates inhabit the no-man's-land of protozoans -- creatures that are clearly not bacteria, but also don't qualify as complex multicellular life, like plants or animals. Each choanoflagellate cell has a tail-like flagellum surrounded by a ring of tiny hairlike structures, like a sperm cell wearing a fluffy Elizabethan collar.
When C. flexa's sheets curl up into a ball with the flagella pointing outward, the ball swims quickly by waving the tail-like structures. Or the sheet can flip into a cup shape by unfolding and then curling in the opposite direction, in such a way that all the flagella face inside.
A series of experiments revealed that the organism reacts to light using a light-sensing protein and other molecules, some of which C. flexa must obtain from the bacteria they eat. What's more, King's team figured out the precise mechanism for the flip: the cells simultaneously flare their collars into a cone shape, bending the sheet of cells and causing a contraction similar to that of an animal's muscle. This inspired the team to look at other choanoflagellates, some of which turned out to have the same ability. The finding suggests this particular contracting mechanism likely pre-dates the first animals.
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Posted by Dr. Tim Sandle, Pharmaceutical Microbiology
