PARENT SESSION
Posters P5D Emerging techniques and systems. Abstracts (731-741)

Spectral properties and energy transfer efficiencies in cell cultures of photosynthetic bacteria. Arlene Haffa^*,1, Denis Klimov¹, Zbigniew Kolber¹, ¹ Monterey Bay Aquarium Research Institute (MBARI), Moss Landing, CA, USA

ABSTRACT- Excitation energy transfer in intact cells of marine aerobic anoxygenic photosynthetic (AAP)bacteria was studied by steady-state fluorescence and ground state absorption measurements obtained within the cavity of an in-house constructed integrating sphere. As expected, direct excitation of any of the bacteriochlorophyll transitions resulted in 900 nm fluorescence. Efficient energy transfer was also found between the S2 states of a subpopulation of carotenoids in the AAPs, which also housed a large population of carotenoids that could be extracted with acetone without altering the basic shape of the fluorescence excitation spectrum indicating that they serve another biological purpose. The existence of these species in open ocean habitats suggests a photoprotective role. Measurements in the purple non-sulfur bacteria Rhodobacter sphaeroides 2.4.1 were taken for comparison. This method also yields absolute extinction coefficients for the photosynthetic units by integrating over all wavelengths or at discreet wavelengths. It can be used to obtain information about the biophysical status, i.e. photosynthetic versus respiratory metabolism, of the cultures under different conditions without breaking the cells or extracting the pigment/protein complexes.

KEY WORDS: in vivo absorption, fluorescence, bacteriochlorophyll a, carotenoids