Fig. 4. (A) The proposed Metal-reducing (Mtr) extracellular electron transfer pathway of S. oneidensis MR-1 which is similar to bacterial metal nanoparticles synthesis outside the bacterial cell surface. CymA, MtrA, MtrC and OmcA are multiheme c-type cytochromes, while MtrB is a porin-like trans-outer membrane protein [this figure has been adapted from ref. 124 with permission from Frontiers]; (B) proposed mechanistic scheme of the biomineralization of gold ions by pullulan exopolysaccharide [this figure has been adapted from ref. 135 with permission from Elsevier].
