Origin of life and heat loving bacteria


SHS=Submarine hydrothermal system

In the last post, i discussed briefly about SHS, here i will be posting some details on why SHS is suitable for life to start. I will be going one by one to help sell the idea on why SHS is good for origins and will show their shortcoming as well

Some of the accepted hypothesis on hyperthermophilles phylogenetic tree. The positions are based on 16S/18S rRNA phylogenic positions29. The root for trees A and B are placed in the bacterial branch30, hence making LUCA a hyperthermophile. In C, the root is placed under the eukaryotic branch making the hyperthermophile a last common prokaryotic ancestor (LCPA)31. D is unrooted, making the LCPA a mesophile.  Adapted from DeLong, E.F, Wu, K.Y, Prezelin, B.B and Jovine, R.V.M (1994) Abundance of Archaea in Antarctic Marine Picoplankton. Nature 371, 695–697
Some of the accepted hypothesis on hyperthermophilles phylogenetic tree. The positions are based on 16S/18S rRNA phylogenic positions29. The root for trees A and B are placed in the bacterial branch30, hence making LUCA a hyperthermophile. In C, the root is placed under the eukaryotic branch making the hyperthermophile a last common prokaryotic ancestor (LCPA)31. D is unrooted, making the LCPA a mesophile.
Adapted from DeLong, E.F, Wu, K.Y, Prezelin, B.B and Jovine, R.V.M (1994) Abundance of Archaea in Antarctic Marine Picoplankton. Nature 371, 695–697

One of the biggest reason associated with origins and SHS, is related to hyperthermophiles. They are microorganism that strive at extreme heat. These organism cultivated from the vents areas could strive at 110 ℃ of heat, which could flourish at temperature up to 110℃. Several authors1,2,3, have proposed that these microbes could have close relation to LUCA. This hypothesis derives from the construction of archaeal and bacterial phylogenetic trees based on 16S rRNA sequence comparisons4. Hyperthermophiles are clustered at the base of these trees and many of their branches are short, suggesting that they have conserved ancestral phenotypic characters3. However, there are also contradicting studies, which indicate that these microbes posses  “missing” enzymes, that uses other energy co-factors, instead of conventional ATP molecule. In other words, this finding shows that these enzymes have adapted to function at high temperature thus indicating that these microbes are more recent than suggested5.

A limitation to this finding is that it assumes that ATP have existed long in time; this argument can be refuted if one also imagine that ATP is also a recent and high adapted energy co-factor in life. This hyperthermophiles, was the first hint which made SHS suitable for origins; however the theory is not limited to this reasons only.

  1. Baross, J.A, and Hoffman, S.E (1985) Submarine hydrothermal vents and associated gradient environments as sites for the origin and evolution of life. Origins of Life and biosphere 15, 327–345.
  2. Pace, N.R (1991) Origin of life–Facing up to the physical setting. Cell 65, 531–533.
  3. Forterre, P (1996) A hot topic: the origin of hyperthermophiles. Cell, 85(6), 789–792.
  4. Stetter, K.O (1994) In Early Life on Earth, S. Bengston, ed. (New York: Columbia University Press), pp. 143–151
  5. Siebers, B and Hensel, R (1993) Glucose catabolism of the hyperthermophilic archaeum Thermoproteus tenax Microbiology Letters. 111, 1–8.
  6. Forterre, P, Confalonieri, F, Charbonnier, F and Duguet, M (1995) Speculations on the origin of life and thermophily: review of available information on reverse gyrase suggests that hyperthermophilic procaryotes are not so primitive. Origins of Life and biosphere. 25, 235–249.
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