The horizontal axis shows the genomic proportion proteins encoding transmembrane helices. The vertical axis shows the ratio of proportions of proteins encoding Sec signal peptides estimated by SignalP-5.0 and SignalP-4.1. RT761 (red), type strains from Thermotogae (green), Dictyoglomi (orange), Caldiserica (pink), and other gram-negative type strains (gray) are plotted (3502 genomes downloadable from the Joint Genome Institute Integrated Microbial Genomes and Microbiomes database). For Thermotogae and other gram-negative type strains, 95% (green) and 99.9% (gray) confidence ellipses are shown respectively. Source data are provided as a Source Data file. (Bottom) Cell structures of select species are shown for “Ca. Atribacteria”, Thermotogae, and Dictyoglomi. The illustrations indicate the outer membrane (black), cytoplasmic membrane (blue), intracytoplasmic membrane (purple), and nucleoid (yellow). *For RT761, the shown schematic requires further investigation to conclude the identity/role of each layer.