SUMMARY: Biosynthetic precursors of carotenoids and hydroxylated carotenoids were substituted for sterol in growth experiments with two representative sterol-requiring mycoplasmas, , strain 07 and avian sp., strain J. Only C dihydroxyl compounds but not biosynthetic precursors supported growth of . These results suggested that all enzymes in the biosynthetic pathway to carotenoids were lacking in this organism. A slight response to phytoene and neurosporene indicated that this species may be capable of hydroxylation of C compounds. Certain precursors of carotenoids and C dihydroxyl carotenoids supported growth of avian strain J. The phosphorylated mevalonic acids did not support growth of this organism, while isopentenyl pyrophosphate produced a response. These results indicated that an enzymic block occurs between mevalonic acid and isopentenyl pyrophosphate. Phytoene, phytofluene, 7ζ-carotene, and neurosporene supported growth of this organism indicating that enzymes probably are present for the conversion of certain C intermediates to dihydroxyl C compound(s). Lycopene and β-carotene did not support growth probably due to the lack of hydro-xylating enzymes for these carotenoids. Monohydroxyl C carotenoids produced a negligible growth response with both organisms. The growth response of both organisms to sarcinaxanthin and lutein indicated that the presence of two hydroxyl groups in the 3,3′-positions is essential for growth. That the carotenol of strain B supported growth is further proof that a dihydroxyl C compound is required for growth (the exact locations of the hydroxyl groups are unknown). Since earlier work has suggested analogous functions for sterol and carotenol the sterol requirement of certain mycoplasma species appears to be the result of the inability of these organisms to effect biosynthesis of carotenols.


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