Fluorescence characteristics of cyanobacteria (blue-green algae)

The fluorescence characteristics of the cyanobacteria Synechocystis aquatilis Sauv., Microcystis firma (Breb. et Lenorm.) Schmidle and Synechococcus leopoliensis (Racib.) Kom. and the green alga Scenedesmus quadricauda (Turp.) Breb. were examined. In the three cyanobacteria, phycocyanin is the main accessory pigment. Phycoerythrin is not present in our investigated strains of cyanobacteria. The highest excitation of the chlorophyll a (Chl a) fluorescence of cyanobacteria resulted from light with wavelengths of 620–630 nm. A definite ‘Kautsky’ effect is also evident at this wavelength. However, excitation with blue light (420–520 nm) produced only very slight fluorescence. The Kautsky effect is not evident at these wavelengths, even at high photon flux densities. For Scenedesmus, fluorescence characteristics typical of green algae were found. The fluorescence excitation of cyanobacteria at 620 nm corresponds to a photosynthesis peak in the action spectrum measured in terms of O2 production. The results underline the necessity of fluorescence measurements at several wavelengths whenever mixed populations are involved. Such measurements also present possibilities for more accurate estimation of biomass and potential photosynthetic production in mixed populations.