On the utilization in vivo of lycopene and phytoene as precursors for the formation of carotenoid glucoside ester and on the regulation of carotenoid biosynthesis in Myxococcus fulvus.

During th logarithmic phase of growth of the myxobacterium Myxococcus fulvus the specific carotenoid content and the molar ratio of the two main carotenoids keto-torulene (3',4'-didehydro-beta,psi-caroten-4-one, 15%) and myxobacton ester (1'-glucosyloxy-3',4'-didehydro-1',2'-dihydro-beta,psi-caroten-4-one ester, 80%) are highly constant. When the formation of these carotenoids was prevented by an inhibitory block at the level of phytoene desaturation, the normal specific content is rapidly reached after release of this block by a two-three-fold enhanced rate of synthesis. The experimentally accumulated phytoene molecules however, are not used as a precursor pool for the formation of the coloured carotenoids. The absolute amount of phytoene does not decrease, although a considerable molecule exchange between this pool and the pathway occurs. Furthermore, experimentally accumulated lycopene is only converted into myxobacton ester when the carotenogenic pathway is blocked at an earlier step, at the level of phytoene desaturation. Without this blockage the lycopene pool remains unaffected. The results are discussed in terms of arrangement of the carotenogenic enzymes in a sort of assembly line in association with the cytoplasmic membrane. Four sites of control are suggested in this pathway.