Cytochrome c reductase is a key enzyme involved in the extracellular electron transfer pathway towards transition metal complexes in Pseudomonas putida

Mediator-based extracellular electron transfer (EET) pathways can balance the redox metabolism of microbes. However, such electro-biosynthesis processes are constrained by the unknown underlying EET mechanisms. In this paper,Pseudomonas putidawas studied to systematically investigate its EET pathway to transition metal complexes (i. e., [Fe(CN)(6)](3-/4-)and [Co(bpy)(3)](3+/2+); bpy=2,2 '-bipyridyl) under anaerobic conditions. Comparative proteomics showed the aerobic respiratory components were upregulated in a bioelectrochemical system without oxygen, suggesting their potential contribution to EET. Further tests found inhibiting cytochrome c oxidase activity by NaN(3)and NADH dehydrogenase by rotenone did not significantly change the current output. However, the EET pathway was completely blocked, while cytochrome c reductase activity was inhibited by antimycin A. Although it cannot be excluded that cytochrome c and the periplasmic subunit of cytochrome c oxidase donate electrons to the transition metal complexes, these results strongly demonstrate that cytochrome c reductase is a key complex for the EET pathway.