Light-harvesting protein complex, molecular model. Peripheral light-harvesting protein complex from the purple bacterium Rhodopseudomonas acidophila. This takes the form of an overlapping circular array of chromophores, with bonding and electron delocalisation effects giving rise to the colours observed. Purple bacteria are phototrophic bacteria that produce energy through photosynthesis. This occurs due to the presence of photosynthetic pigments (bacteriochlorophylls) together with carotenoids that produce colours ranging from purple to red, orange and brown. This complex includes bacteriochlorophyll a.