General description of the 1515 MuF proteins detected in this study. a Schematic representation of the main domain architectures of MuF proteins. MuF proteins containing a MuF domain (blue box) without a C-terminal extension (Ct_ext) are called short MuFs. MuF proteins with a Ct_ext either harbor a known toxin domain (red box) or an unknown domain (gray box). b The inner circle represents the proportion of MuF proteins without Ct_ext (in blue), with a toxin domain (in red), or with an unknown domain (in gray). The outer circle represents their distribution within bacteriophages (in light gray) and bacterial genomes (in black). c Taxonomic distribution of bacteria and of hosts of the phages encoding a MuF protein according to the aforementioned categories. There is a significant association of muf genes encoding toxin proteins with Firmicutes compared to muf genes encoding short proteins (p < 0.0001, two-tailed Fisher's exact test), and there is a significant association of muf genes encoding proteins with a C-terminal extension without known domain with Proteobacteria compared to muf genes encoding short proteins (p < 0.0001, two-tailed Fisher's exact test).
d Association of known toxin domains (red nodes) with MuF domain families (orange nodes) and with other polymorphic toxin families (blue nodes). Only known toxin domains harbored by at least five MuF proteins were reported in this network that includes 172 MuF toxins. The thickness of the edges is proportional to the abundance of the toxin and MuF domain combinations. The size of the orange (MuF families) and red (toxin domains) nodes is proportional to the number of MuF proteins. Toxin domains are described in Additional file 2: Table S7