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Phormidium Flees Fearsome Foe

One might imagine cyanobacteria, residing at the bottom of the food chain, to be an organism made to be eaten, and of course they are, in prodigious amounts. Have they nothing to say on the matter? Surprisingly, they do, claim Edyta Fialkowska and Agnieszka Pajdak-Stós of Jagiellonian University in Krakow.

Noting that ciliates that were fed cyanobacterial mats showed signs of starvation long before the food supply was exhausted, Fialkowska and Pajdak-Stós decided to look at the means by which the prey, mat-forming Phormidium, escape predation. After ruling out poisoning by the cyanobacterium, they focused on the curious observation that cyanobacterial filaments protruding from mats exposed to hungry ciliates almost always ended in empty sheaths. What happened to the trichomes that normally inhabit the sheaths?

It turns out that attack by a ciliate prompts at least one strain of Phormidium to retract itself into its protective sheath, a process that takes seconds. When confronted by the now empty sheath, the ciliate gives up and goes away. Those trichomes that do not respond fast enough get sucked out and eaten by the ciliate. These results have been published in the Proceedings of the Royal Society of London B [(1997) 264:937-941], but it remains for future research to uncover the molecular mechanism by which the cyanobacterium detects its danger and makes its escape.