## 4 Discussion
Many studies have analyzed how environmental conditions (e.g., temperature, pH, and nitrogen and phosphate levels) can increase the biochemical composition of microalgae and cyanobacteria, mainly fatty acids and lipids [48]. These compounds are essential for cyanobacteria. In cells, lipids are found mainly in the cell membranes, featuring mainly polyunsaturated fatty acids (FAs) in their structure. The unsaturated FAs play an essential role in membrane physiology, and the proportion of unsaturated and saturated FA determines membrane fluidity [95]. Several authors have been quantifying the concentration of fatty acids and lipids in cyanobacteria worldwide [17; 27; 28; 30; 36; 47; 48; 96]. Cyanobacteria exhibit high lipid production, as observed in the data collected in Table 5 (119 strains of cyanobacteria). These microorganisms, which can adapt themselves to culture conditions and exhibit high cell growth, are considered ideal lipid sources for pharmaceutical and biofuel production [97]. For example, they produce a wide variety of lipids with antibiotic and antibiotiflm activity [98]. Using these compounds in clinical treatments alone or in association with antibiotics can be considered an alternative to current treatments for human diseases. Examples of commercially important lipids produced by cyanobacteria are polyhydroxyalkanoates (PHAs) and polyhydroxybutrates (PHBs), which are considered a good alternative to synthetic plastics due to their natural origin, optical purity, thermoplasticity, and biodegradability [99]. Cyanobacteria are among the third-generation raw materials that are viable and increasingly studied for use in biodiesel production [100; 101]. Large-scale biodiesel production directly depends on the availability of interesting fatty acids in the raw material. Lipids and fatty acids' total content may depend on the species and strain studied (Tables 1-5), and their content may be altered or induced by different abiotic factors (e.g., pH, mode of operation, photobioreactor configuration, light, and temperature) [102; 103]. Some species of cyanobacteria, such as _Oscillatoria_ sp. FW01, can optimize their yield when cultivated under specific conditions. According to the study by [PERSON] et al. [17], the cultivation of this strain under controlled light and temperature showed a 12% increase in the production of lipids, as well as a 57% increase in that of fatty acids. Thus, the authors considered _Oscillatoria_ sp. FW01 as a raw material to be potentially used for the sustainable production of biodiesel [17]. According to the data gathered in Table 2, it is possible to observe quite a high content of palmitic acid (C16:0) (approximately 36.5%) in the reviewed cyanobacterial species. One of the characteristics of this acid is its small saturated carbon chain with its low oxidation and melting point [104]. These characteristics make this type of acid especially suitable for biodiesel production. The demand for lipids from microorganisms as possible substitutes for fossil fuels has stimulated research into synthetic biofuels. [PERSON] et al. [35] investigated the lipid profile of three strains of Amazonian cyanobacteria (_Cyanobium_ sp., _Limothrix_ sp., and _Nostoc_ sp. ), among which _Limotrix_ sp. showed the best lipid profile and highest amount of C16:0, which are favorable properties for biodiesel production. In addition, it also showed good values of biodiesel quality parameters, i.e., a high oxidative stability (34.9 h) and a cetane number (58.06) above the minimum established by the American Society for Tests and Materials (ASTM). In the work by [PERSON] et al. [105], the _Syntechococcus_ strains were the only ones that exhibited fatty acid profiles mainly composed of C14:0, C16:0, and C16:1 and without polyunsaturated fatty acids. [PERSON] et al. [27] also analyzed the fatty acid profile of the strains of _Mastigocladus laminosus_ (an extremophile found in hot springs), which revealed C16:0 as the main fatty acid (51-53%) and a medium length chain (from C14 to C20). _Nostoc_ sp.