the hypothetical ancestral organism from which to all living beings in earth evolved
Based on molecular studies comparing Archaea, bacteria and Eukaryotes, it is proposed that a hypothetical microbe called LUCA:( the Last Universal Common Ancestor) lived Around 4 billion years ago. By looking for genes common to Archaea and bacteria, one can find out the genome of ancestor to all surviving descendants. Unfortunately, there are only about 355 such genes, mostly for ribosome proteins, proving that LUCA at least had the genetic code. Many other LUCA genes may have been lost in various later lineages over 4 billion years of evolution(A molecular clock model suggests that the LUCA may have lived 4.477 to 4.519 billion years ago, within the Hadean eon ) which can be considered an ancestor to all living organisms.They could have lived a somewhat 'alien' lifestyle, hidden away deep underground in iron-sulfur rich hydrothermal vents (- fissures on the seafloor from which geothermally heated water discharges from underwater vulcanos).Anaerobic and autotrophic, it didn't breathe air and made its own food from the dark, metal-rich environment around it. Its metabolism depended upon hydrogen, carbon dioxide and nitrogen, turning them into organic compounds such as ammonia. Here the source of food was chemical energy. LUCA used molecular hydrogen as an energy source. Serpentinization within hydrothermal vents can produce copious amounts of molecular hydrogen. Plus, LUCA contained a gene for making an enzyme called 'reverse gyrase', which is found today in extremophiles existing in high-temperature environments including hydrothermal vents it appears to have been a small, single-celled organism. LUCA's body, is considered a particle of water in which amino acids are woven together into a living cell by the amazing structure of the DNA, the double helix.It likely had a ring-shaped coil of DNA floating freely within the cell.
If we see the proposed characters of LUCA i.e. as CO2- and N-fixing, H2-dependent, and thermophilic and needed FeS clusters and radical reaction mechanisms and cofactors depending on transition metals, flavins, S-adenosyl methionine etc., it should be confined to a small niche where all these extreme characters are present. This limits the development of LUCA and therefore two groups “Archaea” and “Bacteria” which could adapt to other environments developed further.
Let us hope further studies will unearth the original LUCA!!!!
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Mammen Daniel
