carotenoid biosynthesis spirilloxanthin biosynthesis PMID:22623302 Spirilloxanthin is a carotenoid synthesized by the photosynthetic non-sulfur purple bacterium Rhodospirillum rubrum. It was shown to be aggregated in large particles (apparent MW > 600 kDa) and was not associated with a specific protein. This acyclic, methylated carotenoid, as well as spheroidene, are accessory pigments, in the light-harvesting and reaction-center complexes in Rhodospirillum rubrum. PMID:12745254 UPa:UPA01027 pathway PMID:10880364