I think it is incorrect to talk about multicellularity in most (maybe all) of these examples. I get it, you cannot really treat bacteria exclusively as organisms living in isolation with no concern about their peers, but that is not what biologists mean when they talk about multicellularity. Instead, you can simply consider that the unit of selection is not the individual but the gene, and you can explain all these behaviours very well.
You could say that I am arguing about definitions and you might be right, but calling multicellularity something that is not, erodes the original term: if everything is multicellularity nothing is.
My main reason to complain is that, in fact, there are very good examples in bacteria that meet much better the standard definition of multicellularity (i.e. organisms where different cells perform very different and specialised tasks). For example, some cyanobacteria develop a special type of cell called akinetes which specializes in fixing nitrogen. Because the enzyme that fixes nitrogen is very sensitive to oxygen, these cells lose completely the capacity to do photosynthesis (that releases oxygen and could block the enzyme) and rely on their peers for obtaining many molecules. They also cover themselves with a thick shell to isolate themselves from the atmospheric oxygen. An even cooler example is the Myxobacteria, which create complex structures called fruiting bodies. Some cells sacrifice themselves in the stem to make others (that will become spores) survive. These examples are real examples of basic multicellularity. The other examples given in this post are more related to the fact that bacteria have evolved in communities and not in isolation.
What we consider to be an individual thing should be irrelevant, except that that it tends to carry a lot of intuitive baggage with it. Like, I do find the self-sacrificial behaviors makes more sense when I think of the group of cells as an individual. Note that “what is an individual” is a framing of thought, and not a fact about the world. (Though “X can naturally be thought of as an individual” is a fact about the world.)
On the other hand, there’s the technical terminology. And you’re pointing out that “multicellular” means something specific (it is a fact about the world), that isn’t what Elmer was talking about. And this should be corrected because terminology is important! Would referring to the individual as a “bacterial colony” be more accurate? I think the post could say “colony” or “group of” instead of “multicellular”, without really changing its content.
I think this article is a nice collection of interesting facts about bacteria and I learnt a few new things, don’t get me wrong. It would be even better if it discussed the missing points I mentioned in my comment and reframed the behaviours explained here in the framework of bacteria not developing in the void, there is no need of playing loose with the technical terminology. I would refrain from using multicellularity and other terms that can trigger this knee-jerk reaction from people working on these topics like me.
Thanks for the feedback, the examples you cited are really cool. I didn’t know about akinetes but I’m reading more about them now. For the general point of the article, they might actually be too good examples of multicellularity: there is a pretty strong case that these are multicellular organism by the usual definition. What I wanted to emphasize here is that, even for species like E. coli that are most definitely not multicellular, we can still force ourselves to look at it through a multicellular lens and find interesting things. I agree that it’s awkward to change the definition of a technical term as liberally as I did, so I’ll try to see if I can come up with a better phrasing.
I think it is incorrect to talk about multicellularity in most (maybe all) of these examples. I get it, you cannot really treat bacteria exclusively as organisms living in isolation with no concern about their peers, but that is not what biologists mean when they talk about multicellularity. Instead, you can simply consider that the unit of selection is not the individual but the gene, and you can explain all these behaviours very well.
You could say that I am arguing about definitions and you might be right, but calling multicellularity something that is not, erodes the original term: if everything is multicellularity nothing is.
My main reason to complain is that, in fact, there are very good examples in bacteria that meet much better the standard definition of multicellularity (i.e. organisms where different cells perform very different and specialised tasks). For example, some cyanobacteria develop a special type of cell called akinetes which specializes in fixing nitrogen. Because the enzyme that fixes nitrogen is very sensitive to oxygen, these cells lose completely the capacity to do photosynthesis (that releases oxygen and could block the enzyme) and rely on their peers for obtaining many molecules. They also cover themselves with a thick shell to isolate themselves from the atmospheric oxygen. An even cooler example is the Myxobacteria, which create complex structures called fruiting bodies. Some cells sacrifice themselves in the stem to make others (that will become spores) survive. These examples are real examples of basic multicellularity. The other examples given in this post are more related to the fact that bacteria have evolved in communities and not in isolation.
I would separate these two things:
What we consider to be an individual
Technical terminology, like “multicellular”
What we consider to be an individual thing should be irrelevant, except that that it tends to carry a lot of intuitive baggage with it. Like, I do find the self-sacrificial behaviors makes more sense when I think of the group of cells as an individual. Note that “what is an individual” is a framing of thought, and not a fact about the world. (Though “X can naturally be thought of as an individual” is a fact about the world.)
On the other hand, there’s the technical terminology. And you’re pointing out that “multicellular” means something specific (it is a fact about the world), that isn’t what Elmer was talking about. And this should be corrected because terminology is important! Would referring to the individual as a “bacterial colony” be more accurate? I think the post could say “colony” or “group of” instead of “multicellular”, without really changing its content.
I think this article is a nice collection of interesting facts about bacteria and I learnt a few new things, don’t get me wrong. It would be even better if it discussed the missing points I mentioned in my comment and reframed the behaviours explained here in the framework of bacteria not developing in the void, there is no need of playing loose with the technical terminology. I would refrain from using multicellularity and other terms that can trigger this knee-jerk reaction from people working on these topics like me.
But the article is cool and I enjoyed it :)
Thanks for the feedback, the examples you cited are really cool. I didn’t know about akinetes but I’m reading more about them now. For the general point of the article, they might actually be too good examples of multicellularity: there is a pretty strong case that these are multicellular organism by the usual definition. What I wanted to emphasize here is that, even for species like E. coli that are most definitely not multicellular, we can still force ourselves to look at it through a multicellular lens and find interesting things. I agree that it’s awkward to change the definition of a technical term as liberally as I did, so I’ll try to see if I can come up with a better phrasing.