Action spectrum for carotenogenesis in Myxococcus xanthus.

An action spectrum was measured for photoinduction of colored carotenoids in dark-grown, early stationary-phase cells of Myxococcus xanthus. Maximum activity was observed at 405 to 410 nm with subsidiary maxima at 512, 533, 548, 585, and 635 nm. These maxima correspond closely in position and magnitude with absorption maxima of protoporphyrin IX, which had previously been isolated from M. xanthus cells and had been shown to increase during the stationary phase of the culture. Late stationary-phase, dark-grown cells undergo photolysis which had been shown to have an action spectrum resembling the absorption spectrum of protoporphyrin IX. The similarity of the action spectra of photolysis and photoinduced carotenogenesis in M. xanthus and of other photoinduced biological phenomena is discussed.