And its genome is encased in a membrane:
By definition, microbes are supposed to be so small they can only be seen with a microscope. But a newly described bacterium living in Caribbean mangroves never got that memo… Its threadlike single cell is visible to the naked eye, growing up to 2 centimeters—as long as a peanut—and 5000 times bigger than many other microbes. What’s more, this giant has a huge genome that’s not free floating inside the cell as in other bacteria, but is instead encased in a membrane, an innovation characteristic of much more complex cells, like those in the human body.Elizabeth Pennisi, “Largest bacterium ever discovered has an unexpectedly complex cell” at Science (February 23, 2022)
Because it “blurs the line” between prokaryote like bacteria and eukaryotes like animals, a question naturally arose:
Aside from upending ideas about how big—and sophisticated—microbes can become, this bacterium “could be a missing link in the evolution of complex cells,” says Kazuhiro Takemoto, a computational biologist at Kyushu Institute of Technology.Elizabeth Pennisi, “Largest bacterium ever discovered has an unexpectedly complex cell” at Science (February 23, 2022)
The proposed name is Thiomargarita magnifica.
Tim Standish of Loma Linda University offers us some thoughts about the question of whether magnifica is a missing link:
That was my initial thought as well, but then I put my brain into Darwinist mode and realized that from that perspective I could easily argue that because we see complexity increasing over time among eukaryotes (in reality, I’m not sure that we can), we would also expect the same thing in prokaryotes. Having done that exercise, however, the argument really doesn’t seem that persuasive, in fact it raises some problems:
1.If prokaryotes have the capacity to develop very complex cells, why didn’t they do what eukaryotes did and turn into multicellular organisms, assuming there is some sort of fitness advantage to doing so? Why would being multicellular increase fitness in eukaryotes and not bacteria or archaea? 2. It also occurred to me that when you look at eukaryotes, the most complex cells are not those that are found in what we consider to be the most complex organisms; the really complex ones seem to be single-celled protists, they also have some of the largest genomes. Thus, greater cellular and genome complexity may not be correlated with being multicellular. If that is the case, maybe the fixation on interpretation of morphological complexity–which isn’t the clearest trend anyway–among fossils is misguided. Why not see amoebas as the real triumph of evolution? 3. This raises the question of what being multicellular is really all about. If both prokaryotes and eukaryotes can evolve very complex cells with complex genomes and they thrive as single-celled organisms, why did one lead to multicellular organisms and not the other? Or, is this an example of a very hard discontinuity in biology illustrating the limits of evolution? I guess one could argue that becoming eukaryotic is how prokaryotes became multicellular, but doesn’t that sound quite teleological? I’m not uncomfortable with looking at this as an illustration of the limits of evolution. After about 4 billion years of evolution, is it reasonable to say that prokaryotes lack the potential to become multicellular via the Darwinian process? If this is true with these taxa, what other taxa are constrained in what can be achieved via evolution?