Fig. 6

A hypothetical model for the evolution of the Mtr pathway in Shewanella. a Shewanella may acquire the mtr genes from the ancestor by HGT and exchange with other bacteria. b The geographic origin of 24 Shewanella genomes used in this study. c Selection pressure of mtr genes, with each box showing the ratio of nonsynonymous (dN) over synonymous substitution (dS) rate. Red boxes represent genes that with high ratios, blue boxes represent genes that with low ratios. d Dynamic changed of mtr clusters. Gene gains and losses derived from HGT events and genes duplication. e The metal-reducing pathway of S. oneidensis MR-1 (OM outer membrane, IM inner membrane, MQH2 reduced form of menaquinone, MQ oxidized form of menaquinone). f The depiction of multiple electron transfer pathways of respiration reported in Shewanella