A schematic diagram illustrating the prokaryotic ring of life. The actinobacterial genome donor, at the left (blue), and the clostridial genome donor, at the right (yellow), transfer their genomes to form the doublemembrane prokaryotes at the top of the ring (green). The protein family data identify the Actinobacteria and the Clostridia as donors, and the doublemembrane prokaryotes as the fusion organism.