Chris Kempes

Yeah, so the maximum size is really interesting. That actually concerned us for a long time. So when we first sort of started uncovering what we think was limiting the smallest bacteria, we then had nice sort of laws for how things like growth rate would change with increasing cell volume. And so we thought we understood the trends in bacteria as well as the small limit.

Yeah, so the maximum size is really interesting. That actually concerned us for a long time. So when we first sort of started uncovering what we think was limiting the smallest bacteria, we then had nice sort of laws for how things like growth rate would change with increasing cell volume. And so we thought we understood the trends in bacteria as well as the small limit.

But then we had this huge puzzle about why is it that you don't just keep being bigger and bigger bacteria? Right. So what's happening? You know, the biggest bacteria are growing really fast per unit volume. In fact, growth per unit volume is increasing as bacteria get bigger. you have lots of metabolic power. Everything seems great for the biggest bacteria.

But then we had this huge puzzle about why is it that you don't just keep being bigger and bigger bacteria? Right. So what's happening? You know, the biggest bacteria are growing really fast per unit volume. In fact, growth per unit volume is increasing as bacteria get bigger. you have lots of metabolic power. Everything seems great for the biggest bacteria.

Why do you have this major evolutionary transition to unicellular eukaryotes, which we can get into in a bit, where everything shifts and growth rate decreases and all of that? Why is there a motivation for that? Why aren't we all just giant sacks of bacterial stuff walking around and building cities and talking on podcasts? And

Why do you have this major evolutionary transition to unicellular eukaryotes, which we can get into in a bit, where everything shifts and growth rate decreases and all of that? Why is there a motivation for that? Why aren't we all just giant sacks of bacterial stuff walking around and building cities and talking on podcasts? And

What we proposed as a hypothesis in one of those early papers was it's likely that as growth rate gets faster and faster, eventually the basic biochemistry just can't keep up, right? So... if I have some chemical reaction that can only go at some maximum rate or I have some molecular device that can only work at some maximum rate, eventually it can't keep up with my overall growth rates.

What we proposed as a hypothesis in one of those early papers was it's likely that as growth rate gets faster and faster, eventually the basic biochemistry just can't keep up, right? So... if I have some chemical reaction that can only go at some maximum rate or I have some molecular device that can only work at some maximum rate, eventually it can't keep up with my overall growth rates.

So it just can't keep up with how fast I'm trying to move. I could pump more and more energy into it and it just can't turn over quickly enough. And we were very used to thinking about that with macroscopic machines where they all have an upper threshold where you're just trying to push them too quickly.

So it just can't keep up with how fast I'm trying to move. I could pump more and more energy into it and it just can't turn over quickly enough. And we were very used to thinking about that with macroscopic machines where they all have an upper threshold where you're just trying to push them too quickly.

And so we said, let's look at all of now the detailed biochemistry, all of the macromolecules, all of these different components of the cell, and ask how they change as cells scale up from very small sizes to very large sizes. And as we do that, we see, uh-oh, there's this one component, the ribosome, which again is this device that's sort of the center of biosynthesis.

And so we said, let's look at all of now the detailed biochemistry, all of the macromolecules, all of these different components of the cell, and ask how they change as cells scale up from very small sizes to very large sizes. And as we do that, we see, uh-oh, there's this one component, the ribosome, which again is this device that's sort of the center of biosynthesis.

It's turning genetic information into functional proteins. It's actually building the functional proteins. And we realized for it to keep up with this runaway growth rate, eventually you would need more of that device than you have cell. So you would need to pack more. You need more of this machine that can actually fit inside the cell. We call this the ribosome catastrophe.

It's turning genetic information into functional proteins. It's actually building the functional proteins. And we realized for it to keep up with this runaway growth rate, eventually you would need more of that device than you have cell. So you would need to pack more. You need more of this machine that can actually fit inside the cell. We call this the ribosome catastrophe.

And it sets the largest possible cell size. What's really happening there is that the ribosome is making more ribosomes. So it actually makes some of its own components. And so you reach, it has its own replication rate. So it's a machine that replicates itself with one rate. And eventually the cell growth rate starts to push up against that ribosome replication rate. And that is an impossibility.

And it sets the largest possible cell size. What's really happening there is that the ribosome is making more ribosomes. So it actually makes some of its own components. And so you reach, it has its own replication rate. So it's a machine that replicates itself with one rate. And eventually the cell growth rate starts to push up against that ribosome replication rate. And that is an impossibility.

And so that's where you get one of these, something goes off to infinity. You need infinitely many ribosomes. That can't happen. You overpack the cell. And so we think there's this upper size limit there. Yeah.

And so that's where you get one of these, something goes off to infinity. You need infinitely many ribosomes. That can't happen. You overpack the cell. And so we think there's this upper size limit there. Yeah.

Exactly. And so we did that. So we said, okay, we know where this asymptote is, and let's look at the data. And so interestingly, what you see is that you get less and less species, less and less known species of bacteria as you get closer and closer to this wall. And then we said, well, what's the world record holder bacteria?

Exactly. And so we did that. So we said, okay, we know where this asymptote is, and let's look at the data. And so interestingly, what you see is that you get less and less species, less and less known species of bacteria as you get closer and closer to this wall. And then we said, well, what's the world record holder bacteria?