# Biomolecules from Microalgae and Cyanobacteria: Applications and Market Survey
## 2 Microalgae
### Properties, Taxonomy, and Habitats  
Microscopic in size and giant in their properties, eukaryotic microalgae and Cyanobacteria have a huge assortment of colors and different types of cell organization, e.g., unicellular, colonial, and filamentous. They possess different shapes: spherical (_Porphyridium_), droplet (_Chlamydomonas_), filament (_Oscillatoria_), spiral (_Arthospira/Spirulina_), and even star shape (_Staurastrum_). With a diameter or length of approximately 3 to 10 \(\upmu\)m and a size ranging from 0.2 to 2 \(\upmu\)m, they could be classified into picophytoplankton (0.2-2 \(\upmu\)m), nanoplankton (2-20 \(\upmu\)m), microplankton (20-200 \(\upmu\)m), and mesoplankton (200 \(\upmu\)m-5 mm) [20]. A microalgal cell contains within its cytoplasm many organelles necessary for sound functioning and metabolism. A single cell may contain one or more chloroplasts. They store their \"food\" as starch and fats (Table 1). Due to their simple reproduction, their cell growth systems, and their genetic adaptation amenability, they can quickly proliferate by forming phytoplankton \"blooms\" and survive long term in various harsh environmental conditions (e.g., higher temperature, light intensity, ultraviolet radiations, CO\({}_{2}\) levels, and salinity). They can survive short-term environmental stress by physiological acclimatization triggered by modifying their gene expression. Nevertheless, when environmental stress exceeds their physiological limits, adaptation will be acquired through the selection of several mutations with minor effects [21; 22; 23]. Diverse groups of microalgae have generated the remarkable wealth production of primary and secondary metabolites. These compounds, sometimes with high added value, are synthesized by several metabolic pathways such as photosynthesis, carotenogenesis, lipogenesis, and glycerol synthesis. Efficient coordination and regulation of the different metabolic pathways have been demonstrated, depending on the conditions and depth of culture in marine and freshwater environments. These autotrophic organisms are responsible for 40% of photosynthesis on earth [24]. They transform inorganic matter and light energy into chemical energy and different forms of reserve molecules: \(\alpha\)-(1-4)-d-glucans (such as starches)/ \(\beta\)-(1-3)-d-glucan, fructans, carbohydrates (such as floriodside and triacylglycerors [20]. They have three modes of reproduction: sexual by the union of gametes, vegetative by the division of a single cell or by fragmentation of a colony, and, finally, asexual by the production of mobile spores. Cyanobacteria show enormous biodiversity, and a minority of the described species have been sequenced [25]. They can be either unicellular (_Cluroococcus_) or multicellular (_Arthospira_), with coccoid (_Chroococcus_) or branched filaments (_Anabaena_), singly or grouped into colonies, nearly colorless or intensely pigmented, autotrophic or heterotrophic, psychrophilic or thermophilic, acidophilic or alkalophilic, planktonic or barophilic, dwelling in fresh water or marine environments, including hypersaline environments (salt pans). They are found both free-living and as endosymbionts [26; 27; 28]. They constitute a phylogenetically coherent group of evolutionarily ancient phototrophic Gram-negative bacteria [13] that show a great deal of variety in size, ranging from small forms called picoplankton (less than 2-3 \(\upmu\)m) to larger forms. Cyanobacteria do not contain chloroplast in the cells and keep their energy in reserve in the form of starch or lipids (Table 1). Cyanobacteria are also