INHIBITION OF ACCUMULATION OF BACTERIOCHLOROPHYLL AND CAROTENOIDS BY BLUE-LIGHT IN AN AEROBIC PHOTOSYNTHETIC BACTERIUM, ROSEOBACTER-DENITRIFICANS, DURING ANAEROBIC RESPIRATION

The effects of light on the accumulation of bacteriochlorophyll and carotenoids were investigated in an aerobic photosynthetic bacterium, Roseobacter denitrificans during anaerobic respiration. Accumulation of pigments occurred in darkness but not in white light, with the growth rate being similar under both dark and light conditions. Once pigments had accumulated during growth in darkness, subsequent irradiation with white light did not result in degradation of the accumulated pigments, an indication that the pigments were stabilized in the membranes. The present results, therefore, exclude the possibility of inhibition of the accumulation of the photosynthetic pigments by the photochemical degradation of the pigments in the presence of molecular oxygen and light (blue light). The action spectrum for the inhibition of the accumulation of the pigments showed that light at 470 nm was the most effective and light at wavelengths longer than 500 nm had little inhibitory effect. Together with previous results [Shimada et al. (1992) Plant Cell Physiol. 33: 471], the present data suggest that a signal-transduction system associated with an unidentified blue pigment(s) is involved in the inhibition of the accumulation of the photosynthetic pigments in R. denitrificans.