Figure 1.

Schematic representation of R. capsulatus growth pathways and electron carriers involved in respiration and photosynthesis. The quinol pool (Q pool) is reduced via either the reaction center, or the respiratory NADH and succinate dehydrogenases. During photosynthesis (green), electrons are transferred from the Q pool to cytochrome bc₁ (cyt bc₁). The membrane anchored cyt c_y and soluble periplasmic cyt c₂ carry electrons from the cyt bc₁ to the reaction center. During aerobic respiration (yellow), the cbb₃-type cyt c oxidase is reduced by cyt bc₁ via the electron carrier cyts c₂ or c_y. A cyt bc₁-independent pathway also occurs in R. capsulatus, in which the cyt bd-quinol oxidase is reduced directly by the Q pool.