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Bizarre single-celled life-forms can think and do a happy dance without a brain

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Dec 9, 2019

If you’re convinced you need a nervous system to make decisions or start dancing around when you get excited, you might be in for a shock.

The myth that single-celled organisms are incapable of doing much has now been debunked by two separate studies that might blow your mind. In one, a microscopic aquatic creature was introduced to an irritant and responded by trying out different avoidance behaviors until it finally settled on the right one. In the other, microbes that were fed pieces of space rock not only came back for seconds, but started literally dancing around as if they were thrilled. Even the most overactive imaginations in sci-fi couldn’t make this stuff up.

If I only had a brain … or not

Stentor roeseli is a trumpet-shaped eukaryote — a single-celled organism with a nucleus containing all its DNA — that can (just barely) be seen with the naked eye.

Never mind how primitive that sounds. When researcher Jeremy Gunawardena, associate professor of systems biology at Harvard Medical School, and his team introduced them to irritating particles, the reaction was more of what you’d expect from an organism made up of at least a few more cells. In a study recently published in Current Biology, Gunawardena and colleagues said that the behavior showed "sequential decision-making in the sense that, when given similar stimulation repeatedly, the organism 'changes its mind' about which response to give."

When faced with the irritant, S. roeseli exhibited behavior that made it appear as if it was "changing its mind" on how to best get away from the offending particles until it was finally satisfied. The creature usually attaches to a surface and hangs out unless provoked. The microbes started rejecting the irritants with simpler behaviors, such as bending their cilia (small primordial hair-like structures), but with repeated stimulation, they "decided" to resort to other behaviors such as contracting and even detaching from the surface.

"S.roeseli exhibits avoidance behaviors in a characteristic hierarchy of bending, ciliary alteration, contractions, and detachment, which is distinct from habituation or conditioning," Gunawardena said.

While the S.roeseli didn’t each show the same behaviors in the same order, the scientists concluded that there must be something within these deceptively simple creatures that enables their decision-making process.

So you think you can dance

If single-celled organisms have their own way of thinking, what’s to stop them from dancing?

This is what Tetyana Milojevic and her research team found out when they grew Metallosphaera sedula on a meteorite. The microbes not only gobbled their first helping up but seemed really excited for more. Think happy dance-level excited. Chemolithotropic organisms like M. sedula are able to synthesize inorganic materials like extraterrestrial rock and metal and use them for biological processes. This can explain why they obviously craved more meteorite.

Since "meteorites may have delivered a variety of essential compounds facilitating the evolution of life, as we know it on Earth," as Milojevic and colleagues said in a study recently published in Nature, that shouldn’t be surprising. Neither should the fact that this life-form, much like a tardigrade, is an extremophile that can survive just about anywhere, even the harsh environment of space. Something else that happened during the experiment (whose whole point was really to see if the organism could colonize a meteorite) should.

M. sedula didn’t just grow successfully on the meteorite, but enjoyed it more than you would think a one-celled thing without a brain or nervous system should. "When grown in the presence of NWA 1172, cells of M. sedula were characterized by intensive vivid motility," Milojevic said, referring to the excited movements they exhibited when gorging on meteorite as opposed to a different type of rock.

So maybe the microbes don’t actually know how to dance, but the reaction that was almost like a happy dance GIF under a microscope told the researchers that they more than approved of what was on the menu.

(via Current Biology/Nature)

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