The Cyanophyta is a unique group of prokaryotic microorganisms and a member of a large group of photosynthetic organisms [28]. In contrast to purple and green bac­teria, the photosynthetic mechanism of cyanobacteria is oxygenic and similar to the photosynthesis mechanism in plants and algae. Several filamentous blue-green algae are able to form heterocysts, which contain the enzyme nitrogenase and fix atmospheric nitrogen [29]. Cyanobacteria possess chlorophyll a and phycobilipro — teins as part of their light harvesting antennae [30] . But cyanobacteria lack mem­brane-bound cell organelles (nucleus, mitochondria, chloroplast), which are defining characteristics of the Eukaryotic Kingdom [31]. Cyanobacteria are found elsewhere in marine, brackish water, freshwater, and terrestrial habitats with a variety of mor­phological forms: unicellular and colonial non-motile, colonial, and filamentous [32, 33]. The characteristics of Cyanophyta are presented in Table 2.

Table 2 Cyanophyta species major organic matter characteristics

Characteristic Description References

Nutrient reserves Cyanophycean starch (a-1,4-glucan) as carbon and [31, 492-496]

energy; cyanophycin (arginine and asparagine polymer) as nitrogen storage; polyphosphate as phosphorus storage; poly(hydroxyalkanoate)

Cell wall organization Multiple-layered. Envelope consists of cytoplasmic [497-504]

membrane and cell wall. Optional outer membrane, s-layer, sheath, capsule, and slime. Four-layered peptidoglycan (murein) is principal component.

Consists of glycan backbone with peptide cross linkages

Cyanobacteria are used for a variety of purposes including as a food and feed supplement due to their high protein (Table 3) and vitamin content, as a good source of fiber, and for their good digestibility. Other current and prospective applications of cyanobacteria include the production of pharmaceuticals (antiviral, antibacte­rial, antifungal, and anticancer compounds), enzymes, wastewater treatment, and use as a biofertilizer [34, 35]. Cyanobacterial species are characterized by high productivity (Table 4).