Are Biologists Watching an Evolutionary Leap: One Life Form Absorbing Another?

By Ashley P. Taylor | September 22, 2012 9:30 am

More than 1.6 billion years ago, one cell engulfed another and put it to work. More specifically, a eukaryotic cell, the sort of cell that contains distinct structures with different functions, took in a blue-green bacterium that could do something it could not: use sunlight to make sugars. The ancient eukaryote then reproduced the bacterium in all of its cells, making it a permanent part of the intracellular environment. What was once an independent microbe was now the chloroplast: the cellular structure, or organelle, that plant cells use to photosynthesize. They’ve been together ever since, an absorption known as endosymbiosis.

Nor, scientists think, were chloroplasts the only parts of cells that were once bacteria: Mitochondria, organelles that produce energy in plant and animal cells, got their start the same way, and some other organelles may have, as well. Now researchers have found another useful bacterium that they think is on its way to becoming a modern organelle of another eukaryotic cell—this time, an alga rather than a plant or animal. Studying this relationship would allow scientists to witness endosymbiosis in action, something they had long theorized but never seen.

The alga and the bacterium met in the ocean, and forged a relationship based on nutrient exchange, researchers report in Science. The alga draws energy from sunlight and produces sugars, which the bacterium uses as fuel.  In return, the bacterium processes nitrogen gas into ammonium, which the alga needs. This transfer can occur because the bacterium and the alga live close together, as the scientists know through microscopy and by the fact that the two cell types stayed together during a cell sorting experiment.

In the future, scientists predict, the two will be inseparable; the alga will engulf the bacterium, the bacterium will lose its individual identity and, instead, live as an organelle within the algal cell. The rest will be history.

[via New Scientist]

Image via Thomas Geier/Wikimedia Commons

CATEGORIZED UNDER: Living World, Top Posts
  • Rider

    Imagine if the eukaryotic cell had not gotten together with the blue-green bacterium 1.6 million years ago. Perhaps we would not have plants today. But they did and their bond has never been undone. Imagine how many such symbiotic relationships must have been made to add up to a human being. I wonder what the result will be of the new bond between this alga and bacterium in another million years?

  • Rahim Hankin

    This is nothing new. There are jelly fish native to Palau, Malaysia that have a symbiotic relation with algae that grows on its tentacles. The sunlight indirectly nourished the jellyfish through the algae.

  • blindboy

    Rider, the processes that led from early eukaryotic cells to humans did not involve further symbiotic events but involved re-organisation within the cells, diversification of cell types and the development of specific tissues, organs and organ systems.

  • Tim

    How did the Alga get it’s ammonium before running into this bacterium?

  • bongo

    and try billion in place of million, there is a big difference

  • Rider

    I disagree, blindboy. Obviously you’re right that we are not entirely composed of the result of symbiotic events but considering that we are carrying around more non-human dna than human – and couldn’t survive otherwise – I suggest that there are a great many symbiotic relationships involved within a human. Mostly between single celled organisms we call bacteria whose cells greatly outnumber our own.

  • Katharine

    Considering that the apparent limiting component of their nutrient cycle is nitrogen gas (sunlight will be in abundance for a very long time!), what might this say about the niche a cell with an organelle derived from this bacterium will occupy?

  • Jeff Smith

    A Portuguese Man o’ War, a kind of siphonophore, is not an ‘it’ but a ‘them’ – a colony of four distinct kinds of organism, each adapted to perform a specific function for the benefit of all but unable to detach from the others and survive on its own. What is perhaps most remarkable of all is that all four sprout from a single egg.

  • amphiox

    How did the Alga get it’s ammonium before running into this bacterium?

    From the environment.

    Or from other, free-living bacteria that produce ammonium.

    Or from the ancestors of this bacterium, back before their association was as intimate as it is today.

  • Tim

    Is this article real deductive science or just optimistic assuming that a current theory will, hopefully, prove to be true in a million/billion years? Sounds to me like a theory hoping for future evidence.


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