One- and two-color pump/probe femtosecond and hole-burning data are reported for the isolated B800−850 (LH2) antenna complex of Rhodopseudomonas acidophila (strain 10050). The two-color profiles are interpretable in terms of essentially monophasic B800→B850 energy transfer with kinetics ranging from 1.6 to 1.1 ps between 19 and 130 K for excitation at or to the red of the B800 absorption maximum. The B800 zero-phonon hole profiles obtained at 4.2 K with burn frequencies located near or to the red of this maximum yielded a transfer time of 1.8 ps. B800 hole-burning data (4.2 K) are also reported for chromatophores at ambient pressure and pressures of 270 and 375 MPa. At ambient pressure the B800−B850 energy gap is 950 cm-1, while at 270 and 375 MPa it is close to 1000 and 1050 cm-1, respectively. However, no dependence of the B800→B850 transfer time on pressure was observed, consistent with data for the B800−850 complex of Rhodobacter sphaeroides. The resilience of the transfer rate to pressure-induced cha...