Excitation energy flow in a photosynthetic bacterium lacking B850. Fast energy transfer from B806 to B870 in Erythrobacter sp. strain OCh 114

Abstract

Excitation energy flow in the aerobic photosynthetic bacterium Erythrobacter sp. strain OCh 114 was investigated at physiological temperature by the time-resolved fluorescence spectroscopy in the picosecond time range. This bacterium has two forms of bacteriochlorophyll (Bchl) on separate antenna complexes absorbing around 806 nm (B806) and 870 nm (B870); however, B850 is not detected in this species. Upon selective excitation of B806, the fluorescence from B870 was dominant even in the initial time, indicating that energy transfer from B806 to B870 complexes occurred within the time resolution of the apparatus (6 ps). This fast transfer was confirmed by the fact that no rise term was resolved by the kinetic analysis of the fluorescence from B870. The fast energy transfer suggests tight association between the different classes of antenna complexes. The antenna pigment with energy level lower than that of reaction center was also found in this species (B888) as in some purple photosynthetic bacteria. Its content was estimated to be at most 3 Bchl per reaction center, which is significantly less than that in Rhodobacter sphaeroides.