One Man’s Poison

Years ago I wrote this poem:

       Ode to a Toad
       by George Potts
       ca. 1967

       Oh hail to thee amphibia!
       Gourmets marvel at thy tibia.
       In witches’ caustic cauldrons are thy feet.
       What is one man’s poison ... is another man’s meat.

Now life is once again imitating art. Scientists at NASA have strayed from their quest to justify anthropomorphic carbon dioxide as the bane of our future life here on Earth to discover a form of bacteria that utilizes arsenic as though it were phosphorus. In fact this element, a deadly poison to man, is a fundamental building block in its DNA. See: NASA Discovers

It has long been thought that the six essential elements to living are carbon, hydrogen, oxygen, nitrogen, sulfur and phosphorus. And these are the elements that have been exclusively focused on in our exploration of other planets (and the moon) for the possibility of the existence of life-forms. Now it appears that at least one more element needs to be added to this list … maybe even iron and copper too as they are the transporters of oxygen within higher life forms.

Why is phosphorous a building block of life? After all it was used in many wars as a deadly bomb adjunct … burning through almost anything, Well, for one thing, it forms a weak acid -- phosphoric acid, H(PO4)2, which can interact with weak bases to form many neutral salts. It is also relative plentiful in nature and a phosphate (PO4) is part of the backbone of the DNA strand.  See: DNA Thus, since arsenic is chemically similar to phosphorous in that it has the same number of valence electrons … but with 18 more protons and 26 more neutrons in its nucleus, it might well somehow substitute. See Periodic Table This chemical similarity may also account for its deadly poisonous nature to man since it might easily masquerade as phosphorous in many life-vital chemical reactions.

Now how did arsenic take phosphorous’ place in the DNA construction of this bacterium? I expect it will be discovered that the biosphere in which this bacteria evolved is deplete in phosphorous and abundant with arsenic. And so, after probably millions of false starts, this particular bacterium has found a way of using arsenic as a proxy for phosphorous in it DNA construction. Can life forms find other chemically similar proxies for the six essential elements list in this above paragraph – silicon for carbon, selenium for sulfur, and lithium for hydrogen? Possibly, but I suspect that if any or all of these six basic element to life are totally missing, the hurdles for life-form evolution are so insurmountable as to be effectively impossible.