# Biomolecules from Microalgae and Cyanobacteria: Applications and Market Survey
## 2 Microalgae
### Compositions and Technologies for Photoautotrophic Production of Microalgae and Cyanobacteria
#### 2.3.3 Lipids and Fatty Acids  
Lipids from microalgae and Cyanobacteria are classified into two categories, which are: (i) storage lipids, mainly triglycerides that are non-polar lipids produced by photosynthesis and stored in cells and (ii) structural lipids, such as phospholipids and sterols, which are plastid and cell membrane polar lipids [72]. Microalgae are able to accumulate up to 20-50% of their dry weight in lipids, and this content can reach 80% in response to changes in nutritional and environmental conditions (nitrogen concentration, salinity, or temperature). Furthermore, microalgae contain very rich and diverse fatty acid profiles. The latter are the primary metabolites with 14-20 carbons, belonging to the class of storage lipids mainly used for applications focusing on the production of biodiesel. Saturated and polyunsaturated (PUFAs) fatty acids with more than 20 carbon atoms are used in food as health food supplements and in the pharmaceutical industry for docosahexaenoic(DHA) and eicosapentaenoic (EPA) acids. In addition, the lipid composition of microalgae is very rich in essential PUFAs such as \(\omega\)3, in particular eicosapentaenoic (\(\omega\)3, EPA, C20: 5) and docosahexaenoic (\(\omega\)3, DHA, C22: 6) and \(\omega\)-6 fatty acids. The fatty acid composition of microalgae and Cyanobacteria depends essentially on the species. The _Chlorella_ species are known for their high content of DHA and EPA (3.24% and 8.9% of total fatty acid methyl esters (FAMEs), respectively, in addition to saturated fatty acids). The fatty acids extracted from _Chlorella vulgaris_ are mainly composed of oleic, palmitic, and linoleic acids. The green algae _Haematococcus_ are characterized by its short-chain fatty acids profile with antimicrobial activity, while the Cyanobacterium _Arthrospira/Spirulina_ represents a good source of \(\gamma\)-linolenic acid, sterols, and fatty acids such as palmitic, lauric, oleic acids, and DHA. Diatoms are considered to be a promising source of EPA (15% to 30% of total fatty acids) but not DHA, contrary to dinoflagellates, which have a high potential for use in the commercial production of this compound, which ranges from 12% to 51% of total fatty acids [39; 72; 73; 74]. Different antimicrobial, antiviral, anticancer, and antiprotozoan compounds have been reported from Cyanobacteria. [PERSON] et al. [75; 76] mentioned that lipopolysaccharide from Cyanobacteria have cytotoxic (41%), antitumor (13%), antiviral (4%), antibiotic (12%) activities, and the remaining 18% include antimalarial and antimyctiscone activities. Some Cyanobacteria also have the potential to produce intracellular and extracellular bioactive compounds with potent antibacterial and antifungal activities against many fungi and Gram-positive and Gram-negative bacteria. However, some of the antimicrobial compounds isolated from Cyanobacteria exhibit cytotoxicity and may be ineffective for use in pharmaceuticals [77].  
Cyanobacteria are a source of value-added products such as isoprene, which is an unsaturated, energy-rich hydrocarbon widely used as a biofuel by the chemical industry. Polyhydroxyalkanoates are biodegradable and biocompatible polyesters produced in nature by numerous Cyanobacteria, including _Aphanothece_ sp., _Oscillatoria limosa_, _Arthospira_/_Spirulina_, and the thermophilic strain _Synechococcus_ sp. MA19. This polymer has gained immense attention for industrial applications, such as replacements for conventional non-biodegradable plastics, as well as in the biomedical or pharmaceutical field [78]. Additionally, Cyanobacteria produce a broad spectrum of compounds with anticancer activity. These compounds show potential benefits against cancer, including cell cycle arrest by inhibition of cell growth using apoptotic processes and mitochondrial dysfunctions. For example, some compound extracts from the genus _Arthospira_/_Spirulina_ resulted in the inhibition of homogenous leukoplakia. Others repressed chemically induced carcinogenesis in model hamster buccal pouches [76].