Stinkstoff

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Stinkstoff is my own made-up name for sulfur, with Stoff being the German equivalent of the suffix "gen"  (Stinkstoff = stink begetting). The actual modern German word for sulfur is Schwefel, but there is an older germanic term related to our cognate word brimstone. Van der Krogt does better justice to the word origins here.

I thought a bit about why so many sulfur-bearing compounds smell so badly. Why have we have evolved (or were given) such astonishing olfactory sensitivity to sulfur? Is it a protective defense mechanism? Is this is why our mothers teach us to wash our hands after a number two?

Anaerobic infections are life-threatening. link  A common characteristic of anaerobic microorganisms is their use and production of sulfur-bearing compounds. Chemically, anaerobic organisms rely on sulfur instead of oxygen and use elemental sulfur or even sulfates as electron acceptors. So while aerobic metabolism reduces oxygen to water, anerobic organisms reduce sulfur, "S₂", to hydrogen sulfide, H₂S (the essence of rotten eggs). The smell is the danger signal.

Anerobic organisms are found wherever life without much oxygen is found. Sunlight and fresh air are toxic to many of them. They thrive at the bottom of the sea near hydrothermal vents, in enclosed spaces, and in our guts as E. coli. There is a theory that primitive life was sulfur-based before aerobic plants and bacteria filled the atmosphere with enough oxygen to support life. I wrote a bit about atmospheric oxygen back here.

There is an entire "shadow metabolism" which kicks in for some organisms in the absence of oxygen. Even highly complex coenzymes like vitamin B₁₂ have anaerobic counterparts: cf. S-adensylmethionine, which goes by the alias "Poor Man's B12". Some bacteria even have DNA that encodes both aerobic and anaerobic enzymes and which express them according to living conditions.