Action spectra for inhibition by light of accumulation of bacteriochlorophyll and carotenoid during aerobic growth of photosynthetic bacteria

Action spectra for the inhibition by light of the accumulation of photosynthetic pigments during the aerobic growth of a photosynthetic bacterium, Rhodobacter sphaeroides, and an aerobic photosynthetic bacterium, Erythrobacter sp. strain OCh 114, were determined over the range of wavelengths from 380 to 870 nm. The action spectra for the inhibition of accumulation of bacteriochlorophyll in both R. sphaeroides and Erythrobacter sp. strain OCh 114 indicated that the maximum inhibition occurred at approximately 400 nm and a low level of inhibition occurred at 575 and 770 nm. In R. sphaeroides, the action spectrum for the inhibition of accumulation of carotenoid paralleled that for the inhibition of accumulation of bacteriochlorophyll over the same range of wavelengths. These results indicate that in both species, grown under aerobic conditions, the same photoreceptor is involved in the inhibition. One possible candidate for the relevant photoreceptor may be the precursor(s) to bacteriochlorophyll. It is possible that the photoreceptor is decomposed by light absorbed by itself or by an unidentified photoreceptor that absorbs blue light (a photo-sensitizer). It is suggested that the accumulation of carotenoid is dependent on the stability of the bacteriochlorophyll.