Chris Kempes

And I want to be clear here that I'm not talking about these recent world record holders for the longest bacteria. So there are these almost centimeter long bacteria. Oh, my God. Right? I'm going to lose sleep now. Yeah, exactly. But the key thing to note about those is they're actually filaments. And so they're sort of like a colony of many –

And I want to be clear here that I'm not talking about these recent world record holders for the longest bacteria. So there are these almost centimeter long bacteria. Oh, my God. Right? I'm going to lose sleep now. Yeah, exactly. But the key thing to note about those is they're actually filaments. And so they're sort of like a colony of many –

um little rod-shaped bacteria like e coli stuck end to end and so why they form these very long filaments um there's many copies of the dna and and their dimension in the other radial dimension is is like an e coli it's a it's a small bacterium so they get very long but they don't get volumetrically big and that's really what we're talking about when we say size in this case

um little rod-shaped bacteria like e coli stuck end to end and so why they form these very long filaments um there's many copies of the dna and and their dimension in the other radial dimension is is like an e coli it's a it's a small bacterium so they get very long but they don't get volumetrically big and that's really what we're talking about when we say size in this case

Anyway, we look for the world record holder volumetric organism, something that's roughly a sphere. There we find an organism that's about 100 times bigger than our upper bound. So we thought, okay, this is interesting. How is this thing 100 times bigger than our prediction? Especially since we'd been so pleased by our lower bound predictions. And there's two things to note.

Anyway, we look for the world record holder volumetric organism, something that's roughly a sphere. There we find an organism that's about 100 times bigger than our upper bound. So we thought, okay, this is interesting. How is this thing 100 times bigger than our prediction? Especially since we'd been so pleased by our lower bound predictions. And there's two things to note.

One is this organism has these huge internal storage vacuoles. So it has these big internal membranes that it uses to just store inorganic stuff, likely to be able to grow fast later. So it sort of hoards rare stuff and then uses it later. Um, if you remove all of that and you say, let's just talk about the active sort of metabolic portion of the cell, you're still bigger than our limit.

One is this organism has these huge internal storage vacuoles. So it has these big internal membranes that it uses to just store inorganic stuff, likely to be able to grow fast later. So it sort of hoards rare stuff and then uses it later. Um, if you remove all of that and you say, let's just talk about the active sort of metabolic portion of the cell, you're still bigger than our limit.

Um, not by as much, but still a little bit bigger. And here then the other crucial thing to note is that this organism lives in a really resource poor environment. So it lives in these, um, ocean, deep ocean sediments, um, running a metabolism that we know is a really poor metabolism that just doesn't give you much energy. And so they grow very, very slowly.

Um, not by as much, but still a little bit bigger. And here then the other crucial thing to note is that this organism lives in a really resource poor environment. So it lives in these, um, ocean, deep ocean sediments, um, running a metabolism that we know is a really poor metabolism that just doesn't give you much energy. And so they grow very, very slowly.

In fact, they're really hard to study and grow in the lab, and you have to do so in sort of environmental settings. And so what that tells us is that this upper bound that we were describing really was a speed limit. It said, no, there's a fastest growth rate. There's a fastest replication rate. If you want to get bigger than this wall, you just have to grow more slowly.

In fact, they're really hard to study and grow in the lab, and you have to do so in sort of environmental settings. And so what that tells us is that this upper bound that we were describing really was a speed limit. It said, no, there's a fastest growth rate. There's a fastest replication rate. If you want to get bigger than this wall, you just have to grow more slowly.

And so that's actually what the next branch of life, the unicellular eukaryotes does is they grow more slowly. And that's also what large bacteria that break this rule do is they just stay away from that fast growth limit, that speed limit.

And so that's actually what the next branch of life, the unicellular eukaryotes does is they grow more slowly. And that's also what large bacteria that break this rule do is they just stay away from that fast growth limit, that speed limit.

Exactly, yeah. And it made us realize, to your point, exactly what we were talking about in our theory, what our assumptions were. It was about maximum growth rate. And so we're confident in maximum growth rate, but there's ways to break that law. You can just dial down your metabolism and be a slow-growing organism.

Exactly, yeah. And it made us realize, to your point, exactly what we were talking about in our theory, what our assumptions were. It was about maximum growth rate. And so we're confident in maximum growth rate, but there's ways to break that law. You can just dial down your metabolism and be a slow-growing organism.

Yeah, so there's lots of interesting ideas there, and I think where it interfaces what we're doing is just to ask questions about what are the fundamental bounds on how efficient you can be, how much energy you need to perform a process, and so forth. And we've done a little bit of statistical mechanics on the energetics of different cellular machines.

Yeah, so there's lots of interesting ideas there, and I think where it interfaces what we're doing is just to ask questions about what are the fundamental bounds on how efficient you can be, how much energy you need to perform a process, and so forth. And we've done a little bit of statistical mechanics on the energetics of different cellular machines.

So a bunch of us, including David Wolpert a few years ago, worked out sort of what we thought – the optimal efficiency of something like the ribosome would be and then compared it to the efficiency of the ribosome that we have. And so if you abstract the ribosome, what it really is, is

So a bunch of us, including David Wolpert a few years ago, worked out sort of what we thought – the optimal efficiency of something like the ribosome would be and then compared it to the efficiency of the ribosome that we have. And so if you abstract the ribosome, what it really is, is