# Biomolecules from Microalgae and Cyanobacteria: Applications and Market Survey
## 2 Microalgae
### Properties, Taxonomy, and Habitats
\begin{table}
\begin{tabular}{c c} \hline \hline
**Reserve Form** & **Microalgae** \\ \hline Floridian starch (amylolectin subunits) & Red microalgae \\ Myxophyccal starch & Blue-green microalgae \\ (amylolectin or glycogen-like subunits) & Cross-linked amylose-amylolectin starch \\ Fractans (insulin-like fructose oligosaccharides) & Green microalgae \\ \(\alpha\)-(1-4)-glucan & Cryptophyceae and Dinoflagellate \\ Oil or chrysydaminarin & Chrysophycae \\ Chrysolaminarin & Bacillariophyceaee \\ Paramylon: \(\beta\)-(1-3)-d-glucan & Euglenophyta and Pymnesiophyceaeae \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Reserve molecules from photosynthesis products [20]. called blue-green algae due to the presence of Chl a and phycocyanin located in membrane vesicles called thylakoids, which give the cells a bluish color when present in sufficiently high concentrations. Phycerythrin, a red accessory pigment, can be found as well in these organisms [27]. Cyanobacterial biomass can be estimated at around a thousand million tons (\(10^{15}\) g) of wet biomass; therefore, they are considered among the most important organisms on Earth. Discovered as putative microfossils 2000-3500 million years ago, they are also considered among the oldest organisms in evolution and are believed to be ultimately responsible for the oxygenation of Earth's atmosphere during the episode of the \"Great Oxidation Event\" at the end of the Archean Aeon [13; 28]. Thought to be amongst the first organisms to colonize the earth, these bacteria are predicted to be the photosynthetic ancestors of chloroplasts in eukaryotes such as plants and algae. In addition, Cyanobacteria have the ability to perform photosynthesis, aerobic respiration, and CO\({}_{2}\) and (sometimes) nitrogen fixation. They perform oxygenic photosynthesis like plants and algae, utilizing solar energy and water to generate chemical energy (ATP) and reducing power (NADPH) to fix atmospheric CO\({}_{2}\) and synthesize carbohydrates [13; 29]. [PERSON] (2001) noted that photosynthesis and respiration in Cyanobacteria can take place simultaneously in the same compartment, represented by the thylakoid membrane, thus making this combination a bit unique for them [28]. During photosynthesis, Cyanobacteria use water as an electron donor and produce oxygen as a coproduct. Some filamentous Cyanophyceae are characterized by the presence of specialized cells called heterocysts, which allow the fixation of atmospheric N\({}_{2}\) in anaerby and, therefore, give Cyanobacteria the possibility of growth in inorganic nitrogen-depleted environments [30]. In the dark or under anoxic conditions, Cyanobacteria can perform fermentations for energy generation [31]. It may be due to this flexibility of metabolic pathways that these organisms are able to grow under a wide range of conditions. Unlike eukaryotic organisms, the Cyanobacteria reproduce by vegetative, asexual processes, and sexual reproduction is completely absent. The commonest mode of reproduction among them is undergoing a binary split. Moreover, there have certain specialized structures such as akinetes, hormogonia, hormocysts, and spores, which are partly involved in the process of reproduction [25]. Microalgae and Cyanobacteria are extremely heterogeneous groups gathered around a common characteristic: oxygenic photosynthesis [32]. Among these groups, which exhibit significant taxonomic diversity, the evolution of microalgae was based on the theory of endosymbiosis, according to the characteristics of their mitochondria and plastids [7]. It was proposed that mitochondria originated from the endosymbiosis of \(\alpha\)-proteobacteria by a proteoukaryote, which thereby developed the complex eukaryote cell. The chloroplast, in turn, takes its origin through the primary endosymbiosis of a Cyanobacterium by this heterotrophic eukaryote, also called \"protist\". Endosymbiosis may be the origin of the Plantae kingdom, with primary plastids (formed with only two membranes) comprising phyla of Chlorophyta, Glaucophyta, and Rhodophyta.