Increases in Cellular Levels of Cytochrome cd1 in Roseobacter denitrificans upon Irradiation with Green Light during Aerobic Growth

The cellular level of cytochrome cd₁, the nitrite reductaseof the aerobic photosynthetic bacterium Roseobacter denitrificans,increased considerably when the cells were grown aerobicallyunder white light. The action spectrum for the increase, determinedboth spectroscopically and immunologically, revealed that greenlight at 561 nm was most effective, while blue light between400 and 500 nm was fairly effective. Red and far-red light (650–900nm) absorbed by the bacterio-chlorophyll had no effect, eventhough bacteriochlorophyll and carotenoids were formed normallyduring the growth of cells. Diphenylamine, an inhibitor of thebiosynthesis of carotenoids abolished the increase in levelsof the cytochrome, a result that suggests that a carotenoid(s)was responsible for this phenomenon. The bulk carotenoids seem,however, to be unlikely the candidates for the photoreceptorsbecause they did not accumulate in the light-grown cells. Attemptsto detect archaerhodopsin, 11-cis and all-trans retinal by immunologicalor HPLC analysis were unsuccessful. Although we failed to identifythe photoreceptor, it is clear that R. denitrificans has a green-lightsignal-transduction system that controls the expression of cytochromecd₁. (Received April 19, 1993; Accepted July 12, 1993)