CHON - DNA needs it. S - at least one essential amino acid needs it. P - cells would have no batteries without ADP! I'm interested in the minimal set, and only for known, non-extinct natural prokayotes and eukaryotes (no synthetic life!). Also, only essential for the internal biochemistry of the lifeform, not what might also be essential in its environment. Also, not only essential for the lowest level of dormancy, but also for normal metabolism and reproduction. I know there is a wide range of elements essential for multi-cellular, complex organisms, from Fe, Ca, and Mg to (maybe?) Sn, Se, and even As? So, what else is essential, beyond CHON, S, and P, for the most frugal bacterium or archaean?