Carotenoids and related compounds. Part XXIII. Occurrence of 7,8,11,12-tetrahydrolycopene, spheroidene, 3,4,11′,12′-tetrahydrospheroidene, and 11′,12′-dihydrospheroidene in Rhodospirillum rubrum
Four carotenoids isolated from diphenylamine-inhibited cultures of Rhodospirillum rubrum have been identified by light absorption spectroscopy and mass spectrometry as 7,8,11,12-tetrahydrolycopene (IV), spheroidene (IX), 3,4,11′,12′-tetrahydrospheroidene (VII), and 11′,12′-dihydrospheroidene (XII). The recognition of 7,8,11,12-tetrahydrolycopene (IV) suggests the need for a modification of the Porter-Lincoln series in these photosynthetic bacteria, and the presence of the other three pigments indicates that alternative pathways of spirilloxanthin biosynthesis may be operating.