Separation, characterization and light stability of photosynthetic pigments from Rhodopseudomonas palustris

Abstract:

[Objective] To examine the effects of light on stability of carotenoids (Cars) and bacteriochlorophyll (BChl) a of anoxygenic phototrophic bacteria. [Methods] Using Rhodopesudomonas palustris CQV97 as a reference, we used silica gel column chromatography, HPLC and absorption spectrophotometry for the separation, composition analysis and light stability of Cars and BChl. [Results] The recovery of Cars was higher than that of BChl a whereas the recovery rate of BChl a showed light-dependent fluctuation. Six Cars and trace amount of bacteriopheophytin a (<0.25%) were detected in Car separation fraction. Four intermediates of BChl a including BChl aGG, BChl aDHGG, BChl aTHGG and BChl aP were detected in BChl a fraction, and BChl aP was predominated (76.73%). In the dark, both Cars and BChl a were very stable. Under different light irradiation of 2 000 lx, Cars kept stable within 70 minutes, but it was sensitive to UV radiation and its half-life was about 11.15 min. Under incandescent lamp, fluorescent lamp, natural light and UV radiation, the photodegradation rate constants (min–1) of BChl a were 0.169 8, 0.028 9, 0.213 9 and 0.026 4, corresponding half-lives were 4.47 min, 29.68 min, 4.20 min and 26.19 min, respectively. [Conclusion] BChl a and Cars could be seperated simultaneously by one-step gel column chromatography. Cars were stable toward light irradiation, but sensitive to UV radiation. BChl a was unstable toward light irradiation, the short-term light irradiation resulted in the fluctuation of BChl a recovery rate, a stable intermediate was found in the process of BChl a photolysis. The results will be helpful for refining and functional analyzing of the photosynthetic pigments of the anoxygenic phototrophic bacteria.