Detailed studies of the properties of carotenoids isolated from diphenylamine-inhibited cultures of Rhodospirillum rubrum have revealed a number of novel structures that indicate new features of carotenoid biosynthesis in the photosynthetic bacteria. Both neurosporene and 7,8,11,12-tetrahydrolycopene undergo hydration, methylation and dehydrogenation to yield spheroidene and 11′,12′-dihydrospheroidene respectively; all the intermediates in these pathways have been identified. These pathways represent alternative routes of anhydrorhodovibrin and spirilloxanthin biosynthesis.
