I'm just following trails from the Mrp antiporter derived subunit of the membrane bound hydrogenase of Pyrococcus furiosus. The original Mrp antiporter is, as you would hope, among those 60-odd gene families going right back to LUCA. Excellent stuff in here:
One step beyond a ribosome: The ancient anaerobic core
The final comment in the conclusions is this
"With regard to the most primitive forms of microbial physiology, microbiologists reached the same conclusion 45 years ago , namely that methanogens and acetogens probably represent the most ancient lineages . We required 2000 genomes and powerful computers for our conclusions, while Decker et al. just thought about it. Evidently, just thinking about things can be a source of scientific progress".
That is so cool.