Abstract

This study investigated the properties of antioxidants produced by Rhodobacter (R.) sphaeroides, a purple, non-sulfur photosynthetic bacterium. R. sphaeroides was fractionated into water-soluble and ethanol-soluble fractions, and the ethanol-soluble fraction showed stronger activity. Light irradiation significantly decreased the antioxidant activity of the ethanol fraction. The absorption spectra of the ethanol fraction showed that the peaks of bacteriochlorophyll (BChl) and spheroidene decreased after light irradiation. BChls and carotenoid compounds, which are photosynthetic pigments, were believed to be among the antioxidants in the ethanol fraction. Therefore, BChl a was obtained from R. sphaeroides and evaluated its antioxidant activity. BChl a scavenged DPPH radicals in a concentration-dependent manner. The absorption spectra of the reaction solution showed a decrease in the peak of the DPPH radical at 500 nm, and a decrease in the peak of BChl a at 760 nm and a shift in wavelength, suggesting that BChls exhibit antioxidant activity through their own oxidation and destruction. Therefore, this study suggests that R. sphaeroides produces antioxidants, which include photosynthetic pigments, and thus highlights the potential of photosynthetic bacteria as a source of antioxidants.

Key words: Rhodobacter sphaeroides, Photosynthetic bacteria, Bacteriochlorophyll, Antioxidant, Physiological Functions.