Kolber, Z, S, MBARI, Moss Landing, USA, zkolber@mbari.org
Haffa, A, , MBARI, Moss Landing, USA, ahaffa@mbari.org
Klimov, D, , MBARI, Moss Landing, USA, klimov@mbari.org

MEASURING EXCITATION ENERGY TRANSFER IN AEROBIC PHOTOHETEROTROPHIC BACTERIA

Energy transfer in aerobic anoxygenic photosynthetic bacteria (AAP) was studied by steady-state fluorescence measurements and ground state absorbance measurements obtained within the cavity of an integrating sphere. A method of data correction based on Beer's Law total incident light permits the detection of the absorbance of the Qy transition of bacteriochlorophylls in the IR. The sphere can be used to obtain information about the biophysical status, i.e. photosynthetic versus respiratory metabolism, of the cultures under different conditions. Here this method is used to demonstrate that the ratio of pigment to protein is dictated by light conditions. Under high light more absolute biomass is found based on protein absorbance at 280 nm, but less photosynthetic pigments are present. The loss of spectral properties in cultures that are actually more productive suggests that their numbers in the marine environment may be underestimated using standard fluorescence-based measures. High light also induces an absorbance increase near 250 nm indicative of down-regulation of photosynthetic pigmentation by a flavin-based transcription factor (Aap1) and may be useful in enumerating AAP in natural environments.