Pigment Composition of Two Pigment-Protein Complexes Derived from Anaerobically and Semi-Aerobically Grown Rubrivivax gelatinosus, and Identification of a New Keto-Carotenoid, 2-Ketospirilloxanthin

Abstract

Pigments of two light-harvesting (LH) pigment-protein complexes, LH 1 and LH 2, isolated from the purple bacterium, Rubrivivax gelatinosus, grown anaerobically and semi-aerobically in the light were investigated. In the anaerobic culture, pigment compositions of both LH 1 and LH 2 complexes were approximately equal; OH-spheroidene was the major carotenoid accompanying spheroidene and spirilloxanthin. In the semi-aerobic culture, pigment compositions of both complexes again were approximately equal; an oxidized carotenoid, OH-spheroidenone, was the major component accompanying spheroidenone and 2,2'diketospirilloxanthin. A novel carotenoid of 2-ketospirilloxanthin, an intermediate between spirilloxanthin and 2,2diketospirilloxanthin, was found in both LH complexes from the semi-aerobic culture. Based on these results, we propose the presence of both the spheroidene and the normal spirilloxanthin pathways as the biosynthetic pathway of carotenoids in this bacterium. The oxidation procedure of spirilloxanth in by CrtA was also discussed.