The biggest little guy

by Collin Lysford

Have you heard of Thiomargarita magnifica? At time of writing, it’s the biggest known bacterium in the world. When I say big, I mean it. At around 1cm, it’s visible to the naked eye, over 50 times bigger that anything that had been found before. But the really interesting bit is when it was discovered: 2022.

I think many people have a sense that the natural sciences are now somewhat domesticated. We’ve mapped all sorts of genomes, the Wikipedia page of a living organism has all these nice categories, so we’ve basically figured it all out, right? Well, the first time someone beheld Thiomargarita magnifica, they got the very root level of that classification wrong. It was so big they figured it had to be a fungus. If you’re not looking in the right spot, you’re just not going to find, and that’s true even if you’ve got a principled classififcation for stuff you have found.

I especially love this bit from the Wikipedia page:

Metabolism in bacteria can only occur through the diffusion of molecules of both nutrients and waste through the interior of the bacterial cells, and this places an upper limit on the size of these organisms. The large sulfur bacterium T. namibiensis, discovered in 1999, overcomes this limit by including a large sac filled with water and nitrates. This sac pushes the cell contents to the cell wall, so that the diffusion can work; life processes occur only along the edge” of the cell. T. magnifica s cell includes a similar vacuole[3] that occupies most of the cell (65–80% by volume) and pushes the cytoplasm to the periphery of the cell (the thickness of cytoplasm varies from 1.8 to 4.8 microns.)

You can so easily imagine a biologist in 1998 saying something like While we can never get a definitive answer, we have a strong suspicion that we have seen the largest bacterium, due to fundamental constraints on the geometry of the cell membrame. This isn’t any sort of scientific egotism, but a direct consequence of the square-cube law, burned into the mathematical framework of the universe.” And then T. namibiensis rolls up like I got big water in my tummy :)” and now T. magnificas like wow look I made my tum tum extra big :) :).” Once again, a natural law ended up being more of a natural wet floor sign. Evolution walked a little differently than normal to get where it was going, but the pressure of millions of years has a creativity all it’s own.

The moral of the story: you can still find an order-of-magnitude extreme value across an entire domain of life by just picking up the wet thing and checking whether it’s fungus or not. The age of anecdote is not remotely at an end. It’s not just learning about the natural laws, but also sniffing around for every single way to cheat em.

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On aliveness, pt 1