Light collection and harvesting processes in bacterial photosynthesis investigated on a picosecond time scale

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Abstract
Fluorescence lifetimes were determined for 4 strains of Rhodopseudomonas sphaeroides. Chromatophore samples were excited with a single ps flash, and the fluorescence was detected with a streak camera. The decay times are 100 ps in strains 2.4.1 and Ga, and 300 ps in the carotenoidless strain R-26. These times are related to the transfer of energy from the light-harvesting antenna pigment molecules to the photochemical reaction center. In strain PM-8 dpl, which lacks reaction centers, the lifetime is 1.1 ns. Curves relating the quantum yield of fluorescence to the photon density of the excitation pulse were also obtained. These curves can be fit with a simple model that relates excitonic processes to properties of the photosynthetic unit and that qualitatively describes differences between the mutant strains.