Origin of Life in Hydrothermal Vents?

[lpetrich]

Here are some more features that point to hydrothermal vents as origin-of-life sites.

When rocks lay the groundwork for the origin of life
noting journal paper
A hydrogen-dependent geochemical analogue of primordial carbon and energy metabolism | Nature Ecology & Evolution

Hydrothermal vents contain minerals that can catalyze the combination of hydrogen and carbon dioxide to make organic molecules. These minerals are fairly common ones: greigite (Fe3S4), magnetite (Fe3O4) and awaruite (Ni3Fe), and the hydrogen is formed by water reacting with hot rock and oxidizing it, a process called serpentinization:
2FeO + H2O -> Fe2O3 +H2

An international collaboration of researchers in Germany, France and Japan investigated the catalytic activities of minerals found in deep-sea hydrothermal vents. The results suggest that mineral-driven chemical reactions might be closely mapped onto microbial carbon metabolism.

Life on Earth could not have started without metabolism. Alkaline hydrothermal vents have been proposed as a possible environment where a primitive form of metabolism (protometabolism) predating cellular life could have emerged. The first steps of metabolism, which would have started as geological chemistry, might still be conserved in biochemical pathways that evolutionary biologists have identified as being ancient. One of them is the acetyl-CoA pathway. Microorganisms use it to convert carbon dioxide (CO2) to acetate and pyruvate, serving as an entry point to a more complex carbon metabolism. Interestingly, it is the only known biological carbon fixation route that uses hydrogen (H2) as a source of electrons, and H2 is very abundant in alkaline hydrothermal vent systems. Still, geochemically realistic CO2fixation leading to higher-carbon biomolecules under biologically relevant deep-sea vent conditions has been challenging.

They found:

• formate: HCOOH
• acetate: CH3-COOH
• pyruvate: CH3-CO-COOH
• methanol: CH3OH
• methane: CH4

What might this tell us about the origin of life?

The physiology and habitat of the last universal common ancestor. - PubMed - NCBI
The last universal common ancestor between ancient Earth chemistry and the onset of genetics

The Last Universal Common Ancestor is inferred to have gotten its energy from something called the  Wood-Ljungdahl pathway, a pathway that combines H2 and CO2 to make acetic acid. It's also called the reductive acetyl-CoA pathway, on account of where the acetic acid is assembled, on molecules of coenzyme A. In the process, it does carbon fixation, capturing the carbon in CO2 and making acetic acid with it.

From  Carbon fixation, there are six carbon-fixation pathways known: that one, the Calvin cycle (cyanobacteria/chloroplasts, purple bacteria), the reductive citric-acid/tricarboxylic-acid cycle, and three variants of the 3-hydroxypropionate bi-cycle. The oldest ones are likely the W-L one and the TCA one.

The LUCA is also inferred to have been a thermophile, liking places like hydrothermal vents. Places with these minerals, and places that can catalyze the formation of these biomolecules. So the first organisms' metabolism could simply have taken over from this prebiotic chemistry. Thus supporting Gunter Wächtershäuser's metabolism-first hypothesis.

There would still have been a long way to go to the LUCA, however. It was roughly comparable to some present-day free-living prokaryotes like methanogens, and it likely had a lot of evolution before it. The farthest back that can be plausibly inferred is the RNA world, and that had some complexity of its own, like modifying RNA nucleobases for various functions. It also has the problem that the ribose part of RNA is difficult to make prebiotically, so RNA may have had some predecessor with some alternative to ribose.

But this work helps close the gap between the prebiotic world and the RNA world.

 

[lpetrich]

The LUCA had DNA and proteins, and of these two, DNA is a simple modification of RNA. Proteins are more complicated, and they are assembled by a rather complicated system, but that system uses RNA in all its components.

Scientists have discovered the origins of the building blocks of life - its author seems to have misunderstood a lot, and that's why I'm reluctant to recommend it. It is from
Small protein folds at the root of an ancient metabolic network | PNAS

But it is interesting enough for me to give a better explanation of it. It involved comparing several enzymes involved in electron-transfer and redox metabolism (redox = reduction-oxidation, involving electron transfer), important in biosynthesis and energy metabolism. A result of this comparison was the inference of an ancestral structure, and that gives us a look at a very early protein.

It's not quite the origin of life, however, since in the RNA-world hypothesis, proteins came after the RNA world.