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Plants need light to survive. But apparently, that doesn't have to be sunlight.

Hosted by: Michael Aranda

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Sources:

https://doi.org/10.1073/pnas.0503674102
https://doi.org/10.1038/nrmicro1220
https://doi.org/10.1128/AEM.71.12.8049-8060.2005
https://pubmed.ncbi.nlm.nih.gov/21833341/
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*Intro song*

We're all taught in school how plants 'eat' light. The short version: they take carbon dioxide and water, and thanks to some energy from sunlight, they rearrange the atoms to make oxygen and sugar. We call this photosynthesis, but, apparently, that sunlight portion is optional. I say this because scientists have discovered photosynthesizing bacteria living more than 2300 meters deep in the ocean. Deep enough that there's no sunlight at all. And that's shaken up our idea of where photosynthesis can happen, both on this planet and maybe elsewhere in the universe. The researchers were exploring a deep sea hydrothermal vent. A place where super-hot water heated by magma bubbles out of the seafloor. When they discovered a never-before-seen species of green sulfur bacteria, which the researchers dubbed GSB 1. Green sulfur bacteria are a group of bacteria that thrive in light-filled, low oxygen environments that have lots of sulfur present. Think of an estuary or salt marsh at low-tide with all that rotten egg smelling mud. That's where you'd typically find them. And that's because they can generate their own food using light from the sun, but they don't need oxygen to breathe. They use sulfur ions instead. They even have photosynthetic pigments, known as bacteriochlorophyll, that are similar to the chlorophyll pigments used by plants to capture energy from sunlight. These pigments are located inside structures called chlorosomes, which help funnel light to them. In fact, chlorosomes are so good at this that green sulfur bacteria can live off to next to no sunlight, like in the murky depths of the Black Sea. But there's a whole world of difference between next to no sunlight and no sunlight at all. Like that Black Sea species was discovered at a depth of 100 meters. Where sure, it's dark, but there's still a little bit of sunlight. And researchers know those bacteria require light to survive, because when they put them in true darkness, they didn't grow. So we're left with this weird discovery of a green sulfur bacteria that should need light to survive living so deep in the ocean that there's no sunlight whatsoever. It turns out that no sunlight doesn't mean no light. Hydrothermal vents emit a tiny amount of geothermal light. Basically, the glow of the hot magma that's rising up from the Earth's crust. And, thanks to those super efficient chlorosomes, these bacteria are able to make a living off of that. The light intensity is actually similar to what reaches those Black Sea bacteria. So, it's enough for growth, albeit, barely. I mean, those Black Sea bacteria only divide once every 2.8 years. And this deep sea one probably grows just as slowly. For contrast, your average E. coli bacterium divides every 20 minutes under the right conditions. As for how these photosynthesizers got to those vents, well, GSP 1 bacteria are believed to be the cousins of the Black Sea species and distant relatives of green sulfur bacteria that live in light-filled environments. So they likely drifted down from above and were lucky enough to find the only reliable light in the vast darkness of the deep sea. Researchers haven't yet determined how long ago that happened. They're curious to know though, because this discovery is super exciting. It means that photosynthesis is not limited to the surface of our planet, or anywhere lit by a star. And it makes you wonder, what places, or other planets, might be home to light-eating life? If you often find yourself asking questions like this about the universe, I have a feeling you'd really enjoy what today's sponsor, Brilliant, has to offer. Brilliant is a website and app whose whole goal is to make STEM learning accessible and fun. So gone are the tests and homework and in their place are coding, problem-solving, and other methods for active learning. Maybe this episode inspired you to learn more about light and how it works. Well, you can do that with Brilliant. Their Wave and Light course teaches you everything from the anatomy of a wave to how we measure light. With an annual premium subscription, you can access it, and their dozens of other courses in math, science, computer science, and engineering. And, if you're one of the first 200 to sign up for the subscription at brilliant.org/scishow, you'll get 20% off. Plus, you'll be supporting SciShow, so thank you. 

*Outro music*