# Biomolecules from Microalgae and Cyanobacteria: Applications and Market Survey
## 2 Microalgae
### Properties, Taxonomy, and Habitats
Therefore, photosynthetic membranes of plastids of red algae strongly evoke the thylakoids of photosynthetic bacteria. In addition, the pigment equipment of Rhodophyta (Chl a) and phycobiliproteins resemble that of Cyanobacteria. Other endosymhoes have arisen during the evolution of microalgae, giving rise to organisms with secondary and even tertiary plastids. However, uncertainties relating to the order of appearances and the independence of events still persist. The secondary endosymhois took place between a red algae and a non-photosynthetic host cell and gave rise to the ancestor of all Chromalveolata supergroup: Cryptophyta, Haptopbyta, Ochrophyta (or Heterokontophyta), and Miozoa. This is the most controversial hypothesis in the literature postulated in 1999 by [PERSON] under the name of \"The Chromalveolate Hypothesis\" [33]. By a similar process, Euglenophyta, Cercozoa, and green Miozoa acquired their plastids from ancestral Chlorophyta [34; 35; 36]. Nevertheless, the work described by [PERSON] et al. [37] has shown that the differences observed within these groups cannot be fully explained by this hypothesis. For this reason, another theory called \"The Independent Acquisition Hypothesis\" explains the origin of Chromalveolates by a series of endosymbioses. Therefore, the classification of microalgae is very complex and ambiguous. As mentioned above, it could be based on various different criteria, such as the organization of photosynthetic membranes, but also other criteria such as the chemical nature of storage products and, most commonly, their pigmentation [38; 39]. In addition to the morphological basis, [PERSON] [40] and [PERSON] et al. [41] have proposed a classification of microalgae and Cyanobacteria by means of molecular biology techniques based on the sequence alignments of genes encoding the 16S and 23 SrRNAs for Cyanobacteria and 18S and 28 SrRNAs for microalgae in order to establish family ties between these microorganisms. Other methods, such as the flow cytometer, ensuring semi-automated or fully automated classification, have been recently employed to identify and classify algal species [42]. Currently, there is no specific classification used by the taxonomists since the taxonomic organization may change over the years [43; 44]. As early as their discovery, different kinds of classification of algae were proposed. For example, [5; 45; 46] classified microalgae and Cyanobacteria into 11 and 10 classes, respectively. Contrary to the classification of Frtish, where the 11 th class consists of Cyanobacteria, [PERSON] employed the Procaryota-Eucaryota concept in the classification of microalgae. Table 2 summarizes this classification by implementing the main characteristics of the different classes. Table 3 presents the classification of microalgae and Cyanobacteria, detailing their branches. Those tables show that microalgae and Cyanobacteria are a mixture of different kingdoms: Eubacteria, Protozoa, Chromists, and Plants. This classification is based on data from [PERSON] et al., published in 2015 [47], who detailed the distribution of all living organisms. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline