# Sustainable Microalgae and Cyanobacteria Biotechnology
## 2 Applications of Biotechnology on Microalgae and Cyanobacteria Utilization
### High Valuable Compounds from Microalgae
#### 2.1.2 Superoxide Dismutase  
To maintain the balance of reactive oxygen species, microalgae and cyanobacteria have an effective protective mechanism against highly reactive species produced during the electron harvest-transport chain (ROS). A high accumulation of ROS causes an imbalance in ROS production, resulting in oxidative stress. Some enzyme activities involved in cyanobacteria photosynthesis are mentioned to share a protective mechanism against ROS but act in different ways [45].  
Superoxide dismutase (SOD) is an enzyme found in plants, algae, microalgae (including the Antarctic marine microalgae Chaetoceros brevis), and cyanobacteria that catalyzes the disproportionation of the anion radical to molecular oxygen and hydrogen peroxide. This enzyme protects cells, at least in part, from reactive oxygen species formed during photosynthesis; under normal conditions, the enzymatic protection mechanism maintains the balance of reactive species. ROS are either free radicals, reactive anions containing oxygen atoms, or molecules containing oxygen atoms that can either produce or be chemically activated by free radicals. The main cause of cell damage is the alteration of macromolecules caused by ROS, such as polyunsaturated fatty acids in membrane lipids, essential proteins, and DNA (Figure 1).  
SOD expression is highly regulated, with specific metalloforms acting as inducible protectors in specific cellular compartments. SOD works efficiently during photosynthesis, but little is known about its response to irradiance and oxygen accumulation stresses when these microorganisms grow in photobioreactors. When SOD has maximum accumulation into the cell, SOD accumulation during growth requires a stress event because SOD expression is highly regulated and inducible. Okamoto et al. [46] discovered a significant increase in SOD activity when the microalgae _Tetraselnis gracilis_ was exposed to high cadmium levels. CCAP 19/18 was also reported in another study on the enhancement of SOD production from _Dunaliella salina_. The study found that cultivating these microalgae under high light intensity and nitrogen-depleted conditions resulted in a higher level of SOD than the control condition [47]. There are few reports on the production of SOD in photobioreactors, whether an environmental stress is required, such as increasing light irradiance to the culture, or whether oxygen accumulation in the PBR is required. Microalgae and cyanobacteria grown in photobioreactors under stress conditions could be a good alternative for producing this valuable fine product.  
Extracts of cyanobacteria and eukaryotic algae (red, green, and brown algae, diatoms, _Euglena_, and _Charoophyta_) have been found to contain SOD [48; 49; 50]. In general, these SOD were resistant to cyanide and antibodies against Cu, Zn, indicating the presence of Fe- and/or Mn-enzymes and the absence of Cu, Zn-SOD enzymes, although an aerial green alga lacks Cu, Zn-superoxide dismutase, aquatic angiosperms and ferns, such as other  
been shown to have antimicrobial activity [56; 57]. Other metabolites found in microalgae include astaxanthin, violaxanthin, squalene, lutein, and sulphate polysaccharides, which have been shown to have high antioxidant and antimicrobial activity. Table 3 summarizes metabolites from different microalgal biomass.