Biological complexity: bacteria have complex organelles (Introduction)

by David Turell , Sunday, May 17, 2020, 22:36 (1651 days ago) @ David Turell

Another view of this advanced degree of complexity in bacteria:

https://www.quantamagazine.org/bacterial-organelles-revise-ideas-about-which-came-first...

"In contrast to eukaryotes, which all have a suite of organelles in common, different groups of prokaryotes showcase their own specialized compartments. One kind of bacterial organelle, discovered in 1979, is essentially a little magnet wrapped in a lipid package; another hosts a series of reactions crucial for energy metabolism; still others serve as small storage units for nutrients.

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"The very existence of organelles in these bacteria, coupled with intriguing parallels to the more familiar ones that characterize eukaryotes, has prompted scientists to revise how they think about the evolution of cellular complexity — all while offering new ways to probe the basic principles that underlie it.

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"Among the best studied of the bacterial organelles are the magnetosomes, round structures that build magnetic particles within their lipid bilayer membranes. The organelles allow aquatic “magnetotactic” bacteria to navigate vertically along the Earth’s magnetic fields toward the low-oxygen depths in which they thrive.

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"Some species of planctomycetes contain a membrane-bound organelle called an anammoxosome, which sequesters a chemical reaction that produces nitrogen along with toxic intermediaries. Anammoxosomes act like energy factories for the bacteria, much as mitochondria do in eukaryotes, though anammoxosomes do not seem to be remnants of symbionts as mitochondria are.

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"Those results have been called into question — imaging seems to indicate that the compartment isn’t entirely closed, meaning it does not satisfy the definition of an organelle — but experts remain excited about these bacteria. They have the most complex internal membrane system seen in prokaryotes to date, and they contain proteins that structurally resemble those that shape and maintain eukaryotic membranes. They also seem capable of processes that were thought to be unique to eukaryotes, such as digesting nutrients inside their cells and synthesizing molecules called sterols.

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"Bacteria also seem to have a wide variety of enclosed structures that are bound not by a lipid membrane but by a protein coat. Take carboxysomes, which evolved in bacteria twice, independently, to fix carbon. They and smaller, self-assembling nanocompartments have a polyhedral structure that looks shockingly like a viral capsid, the protein shell that encloses viral genomic material.

"The catalog keeps getting longer: Komeili and his colleagues recently discovered a new lipid-bound organelle that accumulates iron, which they’ve dubbed the ferrosome.

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"No one knows whether the structures seen in bacteria represent primitive, intermediate steps in the evolution of eukaryotic organelles, or separate innovations that evolved independently of those of eukaryotes. It’s possible that the answer varies with each organelle. But even if the bacterial and eukaryotic organelles did evolve completely independently, the prokaryotic structures may be useful for understanding the eukaryotic ones. (my bold)

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"This work not only suggests that compartmentalization is more prevalent among the various branches of the tree of life than people thought; it also indicates that this kind of complexity was not the critical innovation needed to trigger eukaryotic evolution.

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"Rather, eukaryotic characteristics likely emerged as part of a long, gradual trend, just as Rout’s work on the nuclear pore complex demonstrated. “It’s showing us that stepwise evolution is possible,” Devos said, “as opposed to a big explosive change from nothing to everything.”

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"Given that all of life is connected, whether in the deep evolutionary past, this new understanding of evolutionary history can give us more clues about where we came from. At the very least, “people are recognizing that there’s more diversity out there in the environment,” Dacks said, “and that the nice clean stories just don’t cut it anymore.'”

Comment: My bold represents the key point: the evolutionary jump to eukaryote cells may have been much smaller than previously thought, and therefore original bacteria at/after the start of life may have been much more complex than previously realized, implying even more the necessity that a designer was/is required.