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Tuesday, April 20, 2021
Baum cell

Eukaryotic cell has origins questioned

This article is dedicated to Charles Darwin and David Baum. To Charles Darwin because his birthday is this week, February 12th, and to David Baum who exemplifies the humility and cleverness that Darwin himself possessed.

There is a common misconception that science is immutable. Perhaps it is because people believe that once you introduce a scientific theory that works, that’s the end of the road and there’s nothing else to discover. Perhaps it is because the phrase “doing science” is rather allusive: where do scientists get their ideas? How do they do research to test said ideas?

But science really isn’t absolute. Ideas are always evolving, whether due to recent research or improved technology. Sometimes an accepted idea, even the one that’s taught in your Biology 101 lecture, is really just that: accepted. And somewhere out there, possibly in a lab right on campus, somebody is challenging that accepted idea.

That certainly is the case for Dr. David Baum. Baum works in the Botany Department, but he is the first to admit that his work is highly collaborative and extends far past the borders of botany. Professor Baum’s work falls under the category of “the origin of life,” though he’s always studied in other areas of evolution of biology. Baum began thinking about the origin of life when he was an undergraduate and then a graduate student, but he didn’t call it his area of study until recently.

As an undergraduate, Baum had an idea about the origin of the eukaryotic cell. However, Baum’s idea contradicted the proposed “outside-in” theories at the time. Today, the accepted theory for the origin of the eukaryotic cell is called the endosymbiotic theory. It was indeed the theory of the origin of eukaryotes taught in my Biology 101 course two years ago. Lynn Margulis published the theory in the late 1960s. The theory states that a prokaryotic cell, perhaps a large, anaerobic bacterium engulfed a small, aerobic bacterium and formed a symbiotic relationship with it. From this relationship, the aerobic bacterium removed oxygen from the cell and received protection from the bigger bacterium. Eventually, the engulfed bacterium evolved into a mitochondrion and this was the first eukaryotic cell.

However, when David Baum compared a eukaryotic cell to a bacterium, he saw that the bacterium was much more similar to the nucleus of the cell than the whole cell. If the endosymbiotic theory were true, the entire cell should resemble the bacterium.

“Really, what I was trying to do was to go through the logical alternatives. I think it’s good when you have a problem and you think through every possible orientation and direction. It seemed there was a missing hypothesis that hadn’t been proposed. Topologically, it worked to go outwards,” said Baum. “At the time, I didn’t think it was true, but it seems like as any good scientist, we should consider all possible hypotheses before we decide we have the right one.”

In other words, both theories were “outside-in” theories of eukaryotic evolution and Baum wanted to investigate the opposite idea: could eukaryotes have evolved “inside-out”? What if the nucleus was actually the oldest part of the eukaryotic cell? Baum wrote his first essay based on this idea and he recently found the article. “I scanned it and sent it to people. It’s pretty weird; it’s funny how memory is. I thought I had a better argument than I actually did,” said Baum.

Baum’s idea did not come to the fore of his academic investigations until much later. In the intervening years, Baum spent some time in the aforementioned Lynn Margulis’s lab at Boston University. During this time he wrote a second paper. “The second one was much better than the first one,” said Baum.

But the second paper was how far the idea went until recently when Baum began to do research on the origin of life. “When you enter a new field, you don’t have much credibility and much funding. It’s hard to be taken seriously. Were I to finally publish this idea, it would give me a little more credibility to the early evolution of life,” said Baum.

“So, two summers ago, I wrote an essay and I did a lot of reading. The theory sounds a lot better now than it does then,” Baum said. He sent the essay to his cousin, Buzz Baum, a microbiologist from the University College London who, according to Baum, got really excited about it. They spent time editing and supplementing the paper before sending it off to publishers. The fourth journal took the article. The abstract of the article summarizes Baums’ theory: “In brief, we propose that eukaryotes evolved from a prokaryotic cell with a single bounding membrane that extended extracellular protrusions [called blebs] that fused to give rise to the cytoplasm and endomembrane system.”

Since Baum first developed his idea, two major things happened that were really important for supporting their inside-out model. Firstly, scientists recently discovered Archaea. Archaea have the ability to form extracellular protrusions as described in the clip from the Baums’ paper. Thus, based on this knowledge, it is possible that the eukaryote originated from Archaea, rather than bacteria. The second piece of evidence that supported Baum’s hypothesis was the lipids found in eukaryotic membranes. Eukaryotes have some Archaea membranes and some bacterial membrane. How did this happen? In the traditional theories, the larger bacterium swallowed the smaller bacterium, but swallowing a bacterium by phagocytosis is probably not possible with an Archaeal type membrane. In light of the Baums’ theory, the eukaryote cell has bacterial membrane due to passive interactions with bacteria that later became mitochondria and it has Archaeal membranes because the original, larger prokaryote was indeed an Archaea.

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When Lynn Margulis proposed her theory of endosymbiosis, she received scathing criticisms from the science community. However, it seems that the Baums’ theory received more positive responses. “So far, we’ve had lots of really nice emails. We got one from a colleague of Buzz’s who wrote to us that it’s the best paper I’ve read in years. People have been really encouraging, said Baum.

So is it true? “I would give it a greater than fifty-fifty chance that it’s correct, I would say sixty-forty. Buzz is convinced, he’s sure of it, I don’t quite know why. More likely than the alternative,” said Baum. After a moment, he added, “But I still think, it doesn’t matter. Science gets stimulated. It gets people looking at things that people haven’t looked at.”

Indeed, one of the best pieces of advice David Baum has ever received echoes that sentiment. “A colleague that I greatly admired once told me that science is about being wrong and we should always be happy to admit that we were wrong. Because if we’re after the truth, we give it our best shot, and we have to be willing to look at it objectively and say we were wrong, said Baum.

As for David Baum’s current work, it aligns nicely with Darwin Day this Thursday, February 12. He’s working on the origin of life with a motley crew of scientists, with researchers from bacteriology, geosciences, chemistry and, of course, botany. Baum and his colleagues believe that natural selection works on unbounded entities and that it spontaneously happens more frequently than previously believed. In other words, “We’re imposing pre-biotic selection with chemical mixes to tell us how life-like chemistry has arisen,” said Baum.

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