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Very simple cells, such as Nanoarchaeum equitans, require a host to provide certain essential ingredients for life. Complex life-forms (like humans) require a whole ecosystem of other life-forms to survive (either externally, to provide food, or internally, in a symbiotic relationship).

What is the simplest cell that has been discovered so far that can live in an environment where there are no other life-forms, not even in a decomposed state? Does such an organism exist, or is all life inextricably dependent on other life?

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  • $\begingroup$ I guess one of the chemoautotrophs. $\endgroup$
    – WYSIWYG
    Commented Jul 21, 2015 at 15:23
  • $\begingroup$ What kind of environment with 'no other life-forms' are you thinking about? Amino acids are found in comets, and the oxygen in the air is biological in origin. $\endgroup$
    – Resonating
    Commented Jul 21, 2015 at 15:23
  • $\begingroup$ I'm imagining an artificial laboratory environment. I doubt that such an environment would exist naturally so long after the first proliferation of life. $\endgroup$
    – James Newton
    Commented Jul 21, 2015 at 15:31
  • $\begingroup$ @WYSIWYG I'm not sure that the word "autotrophic" is entirely accurate here. I can imagine that there are simple organisms that create their own energy but which require molecules created (and perhaps discarded) by other organisms, so they are still dependent on the other life forms. Does the word "autotroph" explicitly exclude such interdependence? $\endgroup$
    – James Newton
    Commented Jul 21, 2015 at 15:33
  • $\begingroup$ @JamesNewton yes $\endgroup$
    – WYSIWYG
    Commented Jul 21, 2015 at 18:27

2 Answers 2

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If by "simplest" you mean smallest genome, then according to Brock's Biology of Microrganisms (13th ed, p 319) the smallest autotroph is Aquifex aeolicus, a chemolithotroph bacterium. It's genome is 1.5M bases, about 1/3 of that of E.Coli, and was sequenced in 1998 (https://www.ncbi.nlm.nih.gov/pubmed/9537320).

The genome is densely packed though and still carries some 1,500 open reading frames. The authors of the genome sequencing paper states that "metabolic flexibility seems to be reduced as a result of the limited genome size", which I guess is some evidence of "simplicity".

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I'm not sure if this is exactly what you are looking for, but since I was looking for an answer to a similar question to you (what's the simplest living organism), I just found about this,

"The Simplest Living Organism Ever Has 437 Genes and Was Made in a Laboratory"

"a self-replicating bacterium invented by Venter and his team that contains just 437 genes, a "genome smaller than that of any autonomously replicating cell found in nature,"

Now I dont know if artificial organisms count in your question, and if it complies with the other requirements you were asking

https://motherboard.vice.com/en_us/article/craig-venter-created-the-simplest-living-organism-possible-in-a-laboratory

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