The composition of the Bacillus subtilis aerobic respiratory chain supercomplexes

Bacillus subtilis has a bifurcated respiratory chain composed of a cytochrome branch and a quinol oxidase branch. The respiratory complexes of this bacterium have been elucidated mostly by the analysis of the genome and by the isolation of individual complexes. The supramolecular organization of this respiratory chain is not known. In this work, we have analyzed the organization of the supercomplex in membranes isolated from B. subtilis grown in aerobic conditions in a medium with 3 % succinate. We used two different native electrophoretic techniques, clear native electrophoresis (CNE) and blue native electrophoresis (BNE). Using a heme-specific stain and Coomassie blue stain with in-gel activity assays followed by mass spectrometry, we identified the proteins resolved in both the first and second dimensions of the electrophoreses to detect the supercomplexes. We found that complexes b6c and caa3 form a very high molecular mass supercomplex with the membrane-bound cytochrome c550 and with ATP synthase. Most of the ATP synthase was found as a monomer. Succinate dehydrogenase was identified within a high molecular band between F0F1 and F1 and together with nitrate reductase. The type-2 NADH dehydrogenase was detected within a low molecular mass band. Finally, the quinol oxidase aa3 seems to migrate as an oligomer of high molecular mass.