Environments favoring clumpy growth are all that’s needed to quickly transform single-celled yeast into complex multicellular organisms.

During the first 100 days, the clusters in all 15 of the tubes 2x in size. Then they mostly plateaued until the 250th day, when the sizes in 2 of the tubes that didn’t use oxygen started to creep upward again. Around day 350, Bozdağ noticed something in 1 of those tubes. There were clusters he could see with the naked eye. “As an evolutionary biologist … you think it’s a chance event. Somehow they got big, but they are going to lose out against the small ones in the long run — that is my thinking. I didn’t really talk about this with Will at the time.” But then clusters showed up in the 2nd tube. And around day 400, the 3 other tubes of mutants that couldn’t use oxygen kicked into gear, and soon all 5 tubes had massive structures in them, topping out at about 20000X their initial size. “I wasn’t honestly sure if this was a system that would saturate at 1000 cells. We have to continue evolving them and see what they can do. We need to see, if we push these guys as far as we can for decades, for 10000s of generations. If we don’t do that, I will always regret not having taken the opportunity. It’s a once-in-a-lifetime opportunity, to try to push a nascent multicellular critter to become more complex and see how far we can take them.”

2022-11-05: Multicellularity has metabolic benefits

the hollow spheres were Vibrio’s solution to the complicated challenge of eating at sea. An individual bacterium can produce only so much enzyme; breaking down alginate goes much more quickly when Vibrio can cluster together. It’s a winning strategy — up to a point. If there are too many Vibrio, the number of bacteria outstrips the available alginate.

The bacteria resolved the conundrum by developing a more complex life cycle. The bacteria live in 3 distinct phases. At first, an individual cell divides repeatedly and the daughter cells huddle in growing clumps. In the second phase, the clumped cells rearrange themselves into a hollow sphere. The outermost cells glue themselves together, forming something rather like a microscopic snow globe. The cells inside become more mobile, swimming about as they consume the trapped alginate. In the third phase, the brittle outer layer ruptures, releasing the well-fed inner cells to start the cycle anew.
By altering their life cycle to include a multicellular stage, the bacteria can digest the alginate efficiently: Their numbers increase, and the hollow shell helps to concentrate the enzymes. Meanwhile, the structure of the community prevents too many cells from being born. The cells in the shell lose the opportunity to reproduce, but their DNA lives on in the next generation anyway, since all the cells in the orb are clones.