In vivo fluorescence of phycocyanin in combination with multispectral chlorophyll fluorescence spectroscopy - a powerful tool for the analysis of cyanobacteria and algae

Abstract

New approaches for investigation of the photosynthetic apparatus of cyanobacteria are presented. These greatly enhance multispectral and monochromatic methods for the quantitative and qualitative analysis of phytoplankton. The additional usage of the phycocyanin fluorescence signal in combination with our recently developed approach for phytoplankton analysis with chlorophyll fluorescence spectroscopy allows a more detailed study of cyanobacteria and other phytoplankton in-vivo and in-situ. The photosynthetic apparatus of cyanobacteria has a unique composition compared with of other phytoplankton. This is most obvious in the structure of the light-harvesting antennae ¿ the phycobilisomes. All phycobilsomes contain phycocyanin as a pigment. Phycocyanin is therefore a very useful marker pigment for cyanobacterial abundance. Phycocyanin is a fluorescent pigment with an emission wavelength at 650 nm. Fluorescence of cyanobacterial phycocyanin was measured with a new fluorometer at seven excitation wavelength ranges and at three emission channels (650 nm, 685 nm and 720 nm) in vivo. Energy state transitions of phycobilisomes were been observed using variable fluorescence (fv) . No influence on the emission signal at 650 nm has been observed during energy state transitions. An energy distribution model describing energy pathways in the cyanobacterial photosynthetic apparatus was evolved. The model was tested for cyanobacteria grown under various environmental conditions. The influence of yellow substances on pigment determination was measured and minimised. Measurements of phycocyanin concentration were carried out in the presence of other phytoplankton. Correlation of fluorometric results to photometric phycocyanin analysis was calculated. The use of this method for natural phytoplankton communities is discussed.