Energy Transfers in the B808–866 Antenna from the Green Bacterium Chloroflexus aurantiacus

Abstract

Energy transfers within the B808–866 BChl a antenna in chlorosome-membrane complexes from the green photosynthetic bacterium Chloroflexus aurantiacus were studied in two-color pump-probe experiments at room temperature. The steady-state spectroscopy and protein sequence of the B808–866 complex are reminiscent of well-studied LH2 antennas from purple bacteria. B808→B866 energy transfers occur with ∼2 ps kinetics; this is slower by a factor of ∼2 than B800→B850 energy transfers in LH2 complexes from Rhodopseudomonas acidophila or Rhodobacter sphaeroides. Anisotropy studies show no evidence for intra-B808 energy transfers before the B808→B866 step; intra-B866 processes are reflected in 350–550 fs anisotropy decays. Two-color anisotropies under 808 nm excitation suggest the presence of a B808→B866 channel arising either from direct laser excitation of upper B866 exciton components that overlap the B808 absorption band or from excitation of B866 vibronic bands in nontotally symmetric modes.