Suicidal Algae Help Their Relatives and Harm Their Rivals

By Elizabeth Preston | March 11, 2014 9:25 am

chlamy_BG

You might say the benefit of staying alive is an actual no-brainer: even brainless lifeforms do their best not to die. For the most part, anyway. When they’re under stress, single-celled organisms may opt to cut up their DNA and neatly implode. A new study hints that by committing suicide in this way, an organism helps its nearby relatives to stay alive—and hurts its rivals at the same time.

In animals with many cells like us, cellular suicide happens all the time, and it helps keep the whole organism in tip-top shape. As embryos, for example, the cells that form our little paws kill themselves off to make fingers. We’re born with a brain that’s too densely connected, and as we grow the superfluous brain cells die to get things in order. Even as adults, our bodies’ regular upkeep includes constantly adding new cells and commanding older ones to die.

If your entire body consists of one cell, the benefit of killing it is less obvious. Yet various single-celled organisms—from fungi to parasites to bacteria—have been shown to off themselves under stress. 

Pierre Durand, an evolutionary biologist at the University of the Witwatersrand in Johannesburg, has been trying to figure out why. In an earlier study with a single-celled algae called Chlamydomonas reinhardtii, Durand grew cells in the liquid where other cells had previous killed themselves (in response to heat stress). The algae grew faster than usual in the suicide liquid. But liquid where cells had been killed from the outside (the researchers tore them apart with sound waves) was harmful to living cells. A cell that dies suddenly leaks toxic contents into its surroundings, but cells that commit suicide apparently don’t—and even leave behind something healthy for other cells to eat.

Cells that have killed themselves on purpose leave a clear biochemical signature, Durand says. They cut up their DNA in an orderly way, for example, and alter their outer membranes. In a new study, he and his coauthors again stressed out Chlamydomonas reinhardtii cells by heating them. Once more, they looked for the signs of cellular suicide. Then they removed some of the liquid in which the algae had killed themselves. For comparison, they’d also removed some liquid before the cells died. They fed both liquids to new batches of C. reinhardtii cells, as well as two other species of Chlamydomonas.

As before, the cells growing in suicide liquid grew more quickly than controls. But more surprisingly, the two other algae species fared much worse in this liquid. After a few days, their growth tanked, compared to cells grown in pre-suicide liquid.

Durand isn’t sure what materials a suicidal cell could dump into its surroundings that would help its relatives while hurting others. “There are some hints as to how it may work,” he says. The dying cell might release certain resources that the various algae species use differently, or the secret may be in signaling molecules it sends out.

Research by other scientists has also shown that a cell’s suicide can help neighboring cells, Durand says. But not everyone agrees that this is intentional. “Explanations for the origin of programmed cell death are controversial,” he says. Any benefits a cell gets from being near a suicidal cell might simply be an accident.

If it’s true that suicidal cells hurt their rivals, though, while only helping their relatives, then there may be no accident after all. A cell that kills itself under stress would give a boost to relatives that share its DNA. That would mean suicide is a way for a single-celled organism to keep its own genes alive and well—still a no-brainer.


Image: US Department of Energy

Durand, P., Choudhury, R., Rashidi, A., & Michod, R. (2014). Programmed death in a unicellular organism has species-specific fitness effects Biology Letters, 10 (2), 20131088-20131088 DOI: 10.1098/rsbl.2013.1088

  • http://blogs.discovermagazine.com Roy Dempsey

    You say the benefit of death or suicide for one cell of an organism such as this species of algae is not obvious – but of course by the very Darwinian definition of evolution, it is indeed quite obvious. It is the survival of the species and its genes overall as a statistical success over time that counts – not the genes of one individual. On a grandeur scale, this explains why in social insects such as bees and ants, the vast majority of individuals are slaves or sacrificied for the Queen to reproduce and thus carry on the species. On the macro-scale of human societies, this is the similar sacrifice (or ‘duty’) the average worker, the average “drone”, the average soldier must make for the Royalty, the noblemen and women, the Courtiers, to reproduce and carry on – at everyone else’s expense. In Communism, such as in the Chinese cultural revolution under Mao, or in the Stalinist Gulags, we see these “algae” being sacrificied, or sacrificing themselves, for the fitness of the species as a collective whole, or so they would tell us. It is always a struggle for power and influence – whether it is the genes of an algae, a lowly bacterium or the human species.

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Inkfish

Like the wily and many-armed cephalopod, Inkfish reaches into the far corners of science news and brings you back surprises (and the occasional sea creature). The ink is virtual but the research is real.

About Elizabeth Preston

Elizabeth Preston is a science writer whose articles have appeared in publications including Slate, Nautilus, and National Geographic. She's also Editor of the children's science magazine Muse, where she frequently writes in the voice of a know-it-all bovine. She lives in Massachusetts. Read more and see her other writing here.

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