2. Thioautotroph Bacteria

Pre-endosymbiont – “I have to work so hard to scrape together a few HS-, O2 and CO2 molecules just to eek out a living in this undersea vent neighborhood!”
Pre-tube worm host – “ Why don’t you take a load off in my tube chamber? I could use a few extra ergs of ATP from you.”
And the ultimate codependent relationship was born!