Yeast Can Evolve into Multicellular Organisms in a Few Short Months

By Veronique Greenwood | June 23, 2011 12:55 pm


What’s the News: We walking, talking agglomerations of cells have always thought of multicellular life as a profound jump in evolution. The first organisms were just single cells, but at some point, they began to work together for the good of the whole, divvying up tasks like nutrient transport and cellular messaging.  Eventually, these colonies became the complex multicellular life that we know and love.

But maybe being multicellular isn’t as difficult to achieve as we thought. Scientists presenting at the Society for the Study of Evolution conference have, over just a couple months, gotten single-celled yeast to grow into colonies that function as multicellular organisms.

How the Heck:

  • First, to get populations of yeast that would be naturally inclined to stick together, the biologists made it hard for lone cells to survive. They suspended cells in tubes of liquid and then spun them in centrifuges, which caused clumped cells to sink to the bottom, while lighter, singleton cells stayed afloat. While floating cells were discarded, the sticky cells underwent the selection process again and again. The team developed 10 separate strains of sticky cells this way, which they spread on Petri dishes and watched grow.
  • Within 60 days, the cells had developed snowflake-shaped colonies whose reproduction resembled that of a multicellular organism: when a snowflake got large, part of it broke off and formed a new, smaller snowflake.
  • Furthermore, there were tantalizing signs of division of labor in the form of cell death, or apoptosis. When a snowflake grew large, some of its cells killed themselves to make a weak point where a smaller snowflake could break off. While part of a larger organism often sacrifices itself for the good of the whole (such cell death is a major theme of multicellular development, from fruit flies to humans), this isn’t something single cells generally do.
  • The researchers showed that the size at which snowflakes started fragmenting this way changed according to how much evolutionary pressure they put on the colonies, indicating that evolution was occurring on the multicellular level. Selection, in other words, was having an effect on the whole snowflake, not just on individual cells.
  • The sticky cells in each of these snowflakes were genetically identical to each other—each cell had budded off from a mother cell, but had stuck around rather than setting off on its own. Since each colony was a mass of identical cells, it made evolutionary sense that they would cooperate for the good of the group.

What’s the Context:

Not So Fast: While the speed with which these yeast colonies developed multicellular characteristics is pretty exciting, in some ways it’s not that surprising that yeast are capable of banding together. Though today’s yeast are single-celled organisms, they were multicellular in the past, millions of years ago, says Neil Blackstone, an evolutionary biologist at Northern Illinois University in DeKalb (via New Scientist). “I bet that yeast, having once been multicellular, never lost it completely. I don’t think if you took something that had never been multicellular you would get it so quickly,” he says.

The Future Holds: To address that criticism, the researchers plan to try similar experiments with an algae species that has never been multicellular. And they will keep watching the evolution of the snowflakes, as well, to see what other tricks they have up their sleeves, as they work to have the findings published in a journal.

(via New Scientist)

Image credit: Wikimedia Commons

CATEGORIZED UNDER: Human Origins, Living World
  • Torbjörn Larsson, OM

    Even if yeast has the basic toolkit, it is interesting that so little can resurrect it.

    It may indeed take going way back in the tree to make a more interesting test. Already D. discoideum slime molds have evolved a structure analogous to the organized tissue of epithelium in spore stalks. (I.e. a polarized cell layer around an extracellular matrix of cellulose and proteins.)

    And interestingly slime molds used some of the same proteins, for anchoring and orienting the cells in this fruiting body tissue, that was earlier discovered in sponges. (That themselves don’t produce epithelial analogs AFAIU, but descendants animals do.) [Dickinson et al, Science, March 11, 2011.]

    Btw, that sponge link doesn’t work.

    the first time may have been more than 2 billion years ago

    For the record on that truly isolated observation, you yourself published some criticism in another blog post. Or as paleontologist Chris Nedin says:

    “2.1 Ga Multicellular Colonial Organisms – Umm, Not”.

    I think he rather conclusively, and with great example images, shows that bacterial mats may give all of the same remains. (And a pair of paleontologists jump in with “been there, done that” in the comments: “we’ve seen similar things abundantly in a deposit with early pyritisation from Wales”.)

  • Dunc

    Also, it rather depends on which strain of s. cerevisiae they used – we brewers have been (largely unconsciously) selecting for flocculation (clumping together) in yeast for centuries. It’s not necessarily entirely true that they’re strictly single-celled organisms – a phenomenon called “chaining”, whereby daughter cells remain attached to the parent to form long chains of cells (as distinct from “proper” flocculation, which is when formerly separate cells stick together to form clumps), is quite common in many brewery strains.

    Apoptosis is interesting though… Yeast is a fascinating wee beastie. :)

  • m

    The single cell, is very smart. Its doesnt want to do all the work itself when its friends can help. Id say the single cell needs to have a revised description that includes like to be socialable.

  • Noumenon
  • Matt B.

    I don’t understand why clumps of cells would sink and single cells would float. The number of cells doesn’t indicate a change in density.

  • Gary Breitenbach

    thesubject matterand

  • Dee Thibodeau

    Interesting article. Neil Blackstone points out that yeast may have never lost multicellular ancestry, and suggest that these yeast simply activated a vestigial ability to become multicelllular, rather than evolving into something entirely new. I read that scientists at the University of Minnesota (where the study originated) are planning to repeat their experiments with Chlamydomonas, another single-celled organism with no multicellular ancestry. I’m very interested to hear the results of that study.

  • Marcos

    thats why yeast is dangerous if it expires

  • leah

    if yeast is that dangerous, how bout the milk?

  • Guest

    Wooh, hooray for yeast!

  • Taissir N.

    I have read that fungi transforms from unicellular to multicellular. Is it the case in cancer but reversed: where multicellulr transforms into unicellular.

  • Taissir N.

    I have read that fungi transforms from unicellular to multicellular. Is it the case in cancer but reversed: where multicellulr transforms into unicellular.

    { Genetic mechanics
    First-ever 3-D images of DNA damage sensor created at Harvard

    I believe, some lower organisms transforms into another stage of life (or life form) under certain conditions including environmental (cellular, inter-cellular, soundings) stresses. }


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