Ramunas Stepanauskas has recently reported, in Nature publishing group’s ISME Journal, the ancient and remarkably widely distributed “living fossil” lithotroph Desulpforudis audaxviator.
A summary in the 24 April 2021 edition of The Economist (pp. 73-4) says that it "derives its energy by reacting sulphate ions with hydrogen molecules and it scavenges from the rocks it inhabits the carbon and nitrogen atoms that it requires to assemble the organic molecules from which it is built." (Also https://www.bigelow.org/news/articles/2021-04-08.html.)
It appears that this living species, probably well over 100 million years old at the very least, has diffused into what are now three separate continents, is reported to be vulnerable to oxygen and salt, and its DNA has remained remarkably stable across all three locations where is now found.
As far as my chemistry goes (PhD physical & theoretical), it would seem to be surprising if it had managed to evolve DNA from within a rock-bound environment; and if also vulnerable to oxygen, might its earliest ancestor have had to evolve before the Great Oxygenation Event? Might this suggest a possible independent origin of life on Earth?
Either the earliest ancestor of Desulpforudis audaxviator evolved from the very early DNA-based life from which we also have evolved but "soon" found a home in rocks where, presumably, its chemistry changed; or perhaps it evolved in some way independent of the mainstream Tree of Life on Earth, during the Archean?
What you are describing sounds similar to the first form of life on Earth (earliest probably around 4 b.y.ago) which appeared at the bottom of the ocean and was and still is obtaining its energy from the chemicals spewing out of the "black smokers".
It is certainly independent of the photosynthesis group of living things we know from the surface of the planet.
MIchael,
Agreed the lithotrophs and most current life close to hydrothermal vents don't rely on photosynthesis.
The idea of abiogenesis at or close to 'smokers' (e.g. the iron-sulfur world theory of Günter Wächtershäuser) is still one of a number of competing theories at present. Similarly, Tommy Gold's deep-hot biosphere proposal might be even more appropriate for lithotrophs.
If ancestors of lithotrophs like Desulpforudis audaxviator did evolve around smokers, we would then need to explain how they made the biochemical transitions required for rock 'dwelling' and away from toxic salt.
On the other hand, it's hard to see how any DNA-based life could evolve initially without a liquid medium, which near the Earth's surface would very likely be salty.
However, if life did evolve initially around smokers, and depended at first on the greater warmth close to the smokers (preventing them from rapidly spreading far and wide), then I don't see why it might not have begun at more than one such site around the world, if the process was of sufficient probability that repeated initial abiogenesis could occur faster than any one could evolve to both relocate and consume others...
https://en.wikipedia.org/wiki/Hydrothermal_vent
https://en.wikipedia.org/wiki/Abiogenesis#Gold's_deep-hot_biosphere
We have a modern example of a rift forming today in Eritrea right on the surface with many hot springs throwing gases into the air, but also supporting life inside hot pools in the absence of oxygen.
This site is given as an example of a new ocean that will split Africa into 2 or 3 pieces.
Yes - but we'd probably need to see a pattern of DNA (or a totally novel inheritance mechanism) that bears no resemblance to any others on Earth for it to be admitted as of independent origin? (And wait a few million years to see whether the anaerobes are still present as lithotrophs in the new ex-African continents ; - ( )
I expect that most extremophiles have 'relatives' elsewhere on/in Earth, probably only a relatively short distance away from themselves in most cases.
The majority of extremophiles can, I believe, be traced to LUCA.
However, in https://en.wikipedia.org/wiki/Abiogenesis the placement, in a cladogram, of extreme hyperthermophiles alongside but not linked to LUCA seems to be suggesting that they might constitute an independent abiogenesis?
I've often wondered whether DNA can survive the high temperatures in which some thermophiles seem to thrive. There don't seem to be any quick answers on the WWW, but some articles suggest that DNA ('raw' DNA as opposed to that within an organism?) denatures around 80-90 degs-C. (http://www.bioinfo.org.cn/book/biochemistry/chapt12/bio5.htm)
There's also https://en.wikipedia.org/wiki/Nucleic_acid_thermodynamics
and https://en.wikipedia.org/wiki/Denaturation_(biochemistry)
...but the first does what it says: free-energies of melting stability of base pair stacks, while the second is non-quantitative.
(I'd be glad to see a microbiologist give their views here...)
Research on the Candidatus Desulforudis audaxviator (CDa) bacterium has demonstrated a remarkably versatile metabolism. The singular metabolic strategy described for CDa in the Economist article to which you refer is only one of CDa's varied repertoire, suggesting it can also thrive in more benign environments and on more varied substrates. Unlike the extreme environments that characterize hydrothermal vents, CDa is only mildly thermophilic and has been shown to be capable of growth under both aerobic and oxygen-saturated conditions. The fact that the examples recovered at depth from both South Africa and Siberia are hosted in rocks saturated with moderately saline groundwater does not suggest salt intolerance in their natural environment.
Interestingly, the sporulating cells of CDa are associated with gas-bearing vesicles. It has been argued that these function (for example in the closely-related species Desulfotomaculum) as a buoyancy-driven dispersal mechanism which has facilitated migration from deep to active (dispersive) shallow aquifers. If a similar mechanism is involved in CDa, then it may explain the rapid, ongoing, widespread dispersal of CDa. That might also help to account for the genetic similarity of supposedly isolated CDa populations in geographically far-flung areas.
I find this more plausible than the idea that bacterial populations of a single species can become geographically isolated and then undergo minimal genetic differentiation over 100m-year timeframes. The Economist article touts the idea that this evolutionary stasis might be the function of the 'single-species ecosystem' which is presumed to be CDa's only natural habitat. But it is also clear that CDa can, and does, happily co-exist with a wide variety of other lithotrophs under deep subsurface conditions.
None of this suggests to me that CDa's origins might lie in a separate lineage which is somehow 'independent' of the broadly-accepted archaea-bacteria-eukaryota radiation mapped from genome analysis. Furthermore, it is still completely unclear whether extremophiles reflect the primordial environment to which the earliest life adapted, or whether they are derived lineages adapted through time to ever-more extreme environments from progenitors initially adapted to 'benign' environments. The former tends to get more emphasis, I think, partly because so much astrobiological arm-waving depends on it.
de Rezende, Julia Rosa, et al. "Dispersal of thermophilic Desulfotomaculum endospores into Baltic Sea sediments over thousands of years." ISME Journal 1 (2012): 13.
Karnachuk, Olga V., et al. "Domestication of previously uncultivated Candidatus Desulforudis audaxviator from a deep aquifer in Siberia sheds light on its physiology and evolution." The ISME journal 13.8 (2019): 1947-1959.
Kadnikov, Vitaly V., et al. "A metagenomic window into the 2-km-deep terrestrial subsurface aquifer revealed multiple pathways of organic matter decomposition." FEMS microbiology ecology 94.10 (2018): fiy152.
O'sullivan, Louise A., et al. "Survival of Desulfotomaculum spores from estuarine sediments after serial autoclaving and high-temperature exposure." The ISME journal 9.4 (2015): 922-933.