it is a remarkable model for the study of bacterial photosynthesis. R. sphaeroides is a facultative photosynthetic member of the alpha-proteobacteria. The strain can heterotrophically grow not only on aerobic respiration but also on anaerobic condition, as it has diverse metabolic pathways. 2 Although α-C18 of R. sphaeroides is believed to play a role in osmotic adaptation, 1 the exact biological function and roles of α-C18 remains obscure. Catechin discussed in this work is the major component of tea flavonoids, commonly known as a class of flavan-3-ols. The flavan-3-ols are widespread compounds in the plant kingdom and are found in various natural sources including tea leaves, grape seeds, and the wood and bark of trees such as acacia and mahogany. The flavan-3-ols are reported to possess anti-oxidation, antibiotic, anti-virus, and anti-tumor pharmacological activities and also improve the immune system, reduce blood lipids and steroids, etc. 3-8 It was reported that (+)-(2R;3S)-catechin and (−)-(2S;3R)-catechin as chiral drugs showed opposite effects on glycogen metabolism and in membrane fluidity which are responsible for their pharmacological and toxicological mechanisms. 9 It was also reported that (−)-(2S;3R)-catechin has allelopathic activity, but no antibacterial activity. However, (+)-(2R;3S)catechin showed antibacterial activity but no allelopathic activity. 10 Therefore, it is important to consider powerful analytical techniques not only for the evaluation of the total amount of catechin, but also for quantitation of each enantiomer by a rapid and reproducible procedure without tedious and time-consuming pretreatments. The chiral separation of catechin has been performed by high-performance liquid chromatography (HPLC) 11-13 and more recently by capillary electrophoresis (CE) 14-17 with native or modified cyclodextrins as a chiral selector. Recently, a microbial cyclic or noncylic oligosaccharide, produced by sinorhizobial bacteria, was successfully used as a chiral additive for chiral separation of (±)-catechin in CE. 18-21 In the present study, we purified α-C18 from R. sphaeroides