Energy transfer and charge separation in the purple non-sulfur bacterium Roseospirillum parvum

The antenna reaction centre system of the recently described purple non-sul fur bacterium Roseospirillum parvum strain 930I was studied with various sp ectroscopic techniques. The bacterium contains bacteriochlorophyll (BChl) a , 20% of which was esterified with tetrahydrogeranylgeraniol. In the near-i nfrared, the antenna showed absorption bands at 805 and 909 nm (929 nm at 6 K). Fluorescence bands were located at 925 and 954 nm, at 300 and 6 K, res pectively. Fluorescence excitation spectra and time resolved picosecond abs orbance difference spectroscopy showed a nearly 100% efficient energy trans fer from BChl 805 to BChl 909, with a time constant of only 2.6 ps. This an d other evidence indicate that both types of BChl belong to a single LH1 co mplex. Flash induced difference spectra show that the primary electron dono r absorbs at 886 nm, i.e. at 285 cm(-1) higher energy than the long wavelen gth antenna band. Nevertheless, the time constant for trapping in the react ion centre was the same as for almost all other purple bacteria: 55 +/- 5 p s. The shape as well as the amplitude of the absorbance difference spectrum of the excited antenna indicated exciton interaction and delocalisation of the excited state over the BChl 909 ring, whereas BChl 805 appeared to hav e a monomeric nature. (C) 2000 Elsevier Science B.V. All rights reserved.