INCREASES IN CELLULAR-LEVELS OF CYTOCHROME CD(1) IN ROSEOBACTER-DENITRIFICANS UPON IRRADIATION WITH GREEN LIGHT DURING AEROBIC GROWTH

The cellular level of cytochrome cd(1), the nitrite reductase of the a erobic photosynthetic bacterium Roseobacter denitrificans, increased c onsiderably when the cells were grown aerobically under white light. T he action spectrum for the increase, determined both spectroscopically and immunologically, revealed that green light at 561 nm was most eff ective, while blue light between 400 and 500 nm was fairly effective. Red and far-red light (650-900 nm) absorbed by the bacteriochlorophyll had no effect, even though bacteriochlorophyll and carotenoids were f ormed normally during the growth of cells. Diphenylamine, an inhibitor of the biosynthesis of carotenoids abolished the increase in levels o f the cytochrome, a result that suggests that a carotenoid(s) was resp onsible for this phenomenon. The bulk carotenoids seem, however, to be unlikely the candidates for the photoreceptors because they did not a ccumulate in the light-grown cells. Attempts to detect archaerhodopsin , 11-cis and all-trans retinal by immunological or HPLC analysis were unsuccessful. Although we failed to identify the photoreceptor, it is clear that R. denitrificans has a green-light signal-transduction syst em that controls the expression of cytochrome cd(1).