As a non-biologist, I assume that there are certain elements that occur in all life forms as we know them. Examples might be carbon, hydrogen, oxygen and so forth. There are also elements that are rarely, if ever, required for life on earth. My question is not about what elements might be required for life (although such information might be interesting for me and other readers). Rather it is about what the minimum possible number of elements that any life form on earth has, if we know the answer to that question. Also, if it is known, (how) does this differ between the plant, animal and other kingdoms?

You are far more likely than me to know what tags might be appropriate here. Please feel free to edit.

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    $\begingroup$ Prions are self-replicating proteins that can turn other proteins into more prions, they cause diseases like Creutzfeldt-Jakob disease (vCJD is also known as "mad-cow disease"), they replicate, evolve etc... don't worry, they aren't really alive, but then neither are viruses technically, which can't replicate themselves independently of another organism and always need some part of that organisms replication machinery to function. However, if you accepted prions as life, the minimum would be C, H, O, N, S I think. $\endgroup$ – bob1 May 13 at 4:51
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    $\begingroup$ I think I would add P to the list provided by @bob1 (ATP/NAD) $\endgroup$ – user338907 May 13 at 11:18
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    $\begingroup$ Hmmm. Four downvotes, but no constructive comments to explain how to ask a better question. Sigh ... $\endgroup$ – Araucaria May 13 at 21:21
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    $\begingroup$ @Araucaria - The reason for the down-votes is likely that it is impossible to define because there is such a variety of life that there will be no 1 magic number of elements. The most we can do is list a minimum of elements that are found in all life-forms, which would presumably make life possible, but that is specifically not what you asked for. $\endgroup$ – bob1 May 13 at 23:27
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    $\begingroup$ minimum to have any life or life as earth currently has? $\endgroup$ – John May 14 at 2:45

If we change the question to "what is the minimum number of elements common to every form of life?", my lists would be as follows. (I am not considering either viruses or prions to be 'alive').

The following elements are surely common to all forms of life (List 1):

H (1), C (6), N (7), 0 (8), Mg (12), P (15), S (16) [#7].

In addition, the following elements are very likely to be common to all forms of life (List 2):

Na (11), Cl (17), K (19), Ca (20), Fe (26), Cu (29), Zn (30) [#7].

If we broaden things to include elements occurring in any form of life I would add (List 3):

B (5), F (9), Si (14) [!Seemingly], V (23), Cr (24), Mn (25), Co (27), Ni (28), Se (34), Mo (42), Cd (48), Sn (50) [!Maybe], I (53) , W (74) [#14].

  • No element in either list has an atomic number greater than 74 (Tungsten). (In the list given by Frieden (1972), the highest is I (53)).

  • For List One (and as pointed out by @bob1), H (1), C (6), N (7), 0 (8), S (16) are all present in proteins. P (15) is present in ATP and NAD. We must surely also include Mg (12), as the true substrate of almost all ATP-requiring enzymes is a complex of Mg++ and ATP. I can't see that any element can be removed from this list, but it could be argued that we need to add some from List 2.

  • For List 2, Fe (26) is present as haem in haemoglobin and the cytochromes, and (not necessarily complexed to heme) in other components of the electron transport chain. It might be possible that anaerobic life is possible without iron, in which case Fe (26) needs to be demoted to List 3 (but I doubt it). Zn (30) occurs in many enzymes (including yeast and liver alcohol dehydrogenase). It might be possible for a life form to exist without requiring Zn, but I don't know of any examples.

  • If we restrict consideration to plants, then Mn (25) needs to be promoted to List 1 (Mn is an essential component of Photosystem II, the enzymic system responsible for the 'splitting' of water in photosynthesis). As life as we know it would be impossible without PS, Mn (25) should possibly be in List 1 without qualification.

List 3 will probably always be contentious, but here are my thoughts:

This, I think, justifies B being included in List 3: required for some forms of life (but not a minimum requirement for life).

I think The chemical elements of life by E.Frieden, published in Scientific American in 1972, is still relevant, and I have relied heavily on the table on p55 of this publication in compiling the above lists

I haven't considered Sr (38), Nb (41), Ba (56) or Ta (73) but from Tungsten in biological systems it appears that there is a case for these elements to be included in List 3

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    $\begingroup$ Should I take it, then, that there may be life forms that have only around 14 elements (list 1 + list 2)? $\endgroup$ – Araucaria May 14 at 1:29
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    $\begingroup$ Note boron is important in cyanobacteria. plantphysiol.org/content/plantphysiol/94/4/1554.full.pdf and there a few notable organoboron compounds. www2.chem.wisc.edu/areas/reich/OrgMet/boron.htm $\endgroup$ – John May 14 at 2:42
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    $\begingroup$ I think you can safely move Fe into list 1, even if heme (or haem) had never existed, Iron-Sulfur cluster proteins are ubiquitous among all cellular life, including obligate anaerobes. I can only think of one synthetic biology experiment in which E. coli was engineered to grow (very slowly) without making new Fe-S clusters, but they didn't even attempt to show growth in iron-limiting conditions. You're also probably right about being able to move Mn and Zn up to list 1 without further qualification. $\endgroup$ – MikeyC May 14 at 18:21
  • $\begingroup$ @MikeyC Thanks. I agree with all you say, especially about non-heme iron. (Will update again over the weekend) $\endgroup$ – user338907 May 14 at 19:24

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