**3. Examples of fluorescent microscopic spectroscopy application**

The detailed description of the morphology, structure, chemical and optical properties of light-harvesting complex of cyanobacteria, phycobilisomes and phycobilins can be found in numerous publications [55–72]. On the other hand, the fluorescence properties of the intact living cyanobacterial cells differ drastically from the properties of the detached phycobilisomes and its components and originate from the efficiency of the energy transfer between all components of the energy transfer chain included the final step, the delivery to PSII or PSI. Each transfer step result in the spectrum shape as a peak or shoulder. Moreover, fluorescence of photosynthetic pigments in the intact cells is affected by physicochemical and physiological processes that occur within and across the thylakoid membranes. Here we demonstrate on several examples how these peculiarities can be used for investigation of physiological state and biological diversity of cyanobacteria.

The correct identification of cyanobacterial cultures and estimation of their physiological state are quite important in the environmental monitoring and industrial applications. The ability to detect small variations in the physiological state of cyanobacterial culture under weak external treatments is quite desirable in both field and laboratory experiments. The fluorescent CLSM technique is a very powerful tool that can support any on-line field, laboratory and technological study. In addition, the results of single-cell spectroscopic analysis are much more suitable for further statistical and analytical calculations then the conventional optical methods of investigations. In this chapter, we present several examples of practical application of the described CLSM technique.
