# Exopolysaccharides from Cyanobacteria: Strategies for Bioprocess Development
## 3 Cyanobacterial Bioprocess (Cyano-EPS) Development
### Production and Optimization
#### 3.2.2 Process Conditions  
Process conditions and respective control are important to assure the reproducibility and feasibility of the bioprocess. Nevertheless, these settings can possibly influence the desired outcome of the process. Cyanobacteria can grow in pH ranging from 6-12, while the initial pH was shown to affect the number of EPS produced [47; 48]. CO\({}_{2}\) is thought to increase EPS production in planktonic cyanobacteria [71]. Setting a pH range to control the cultivation period either through injection of CO\({}_{2}\) or the use of acid/basic solutions avoids the limitation of growth before light, which is the ultimate limiting factor for photoautotrophic cultures like cyanobacteria [49; 53; 54; 70; 72]. The growth rate of cyanobacteria has been observed to increase with shear stress, probably by promoting orientation and increasing the contact area of the microorganisms and nutrients [73; 74]. For the Cyano-EPS a certain degree of shear stress will be necessary once the rheology of the medium is altered and the mass and gas transfers become less efficient throughout the time. The evolution of culture medium rheology combined with shear stress highly affects the bacterial EPS production at the industrial scale [55]; however, reports have shown a variety of shear stress applied most of the times by default, single aeration [33; 58] or agitation [47; 59; 60; 69], aeration with CO\({}_{2}\) supplementation [53; 54; 64; 70; 75; 76], simultaneous aeration, and agitation [49; 56; 57]. Optimization studies demonstrated a low number of reports studying the effect of shear stress on EPS production [54; 56; 65; 70], whereas the majority of them found it highly relevant. Temperature is also reported to have a positive effect on growth and EPS production [56; 57; 65; 70], though others have reported a dissimilitude [75; 76]. When combining the effect of temperature and light intensity the settings for EPS enhancement are antagonists [75]. A petri dish work using crossed gradients of temperature and light intensity have found the optimal range for growth and EPS for _Scytonema topyotrichoides_ and _Tolyotthrix bouteillei_. These two strains from the same microhabitat had different light and temperature optima, supporting, even more, the strain specificity on Cyano-EPS control. Moreover, the temperature was shown to be the most significant parameter [77]. Light/Dark (L/D) cycles highly affected the production of insoluble carbohydrates per cell [78]. The optimization studies found positive correlation by applying L/D cycles [54; 56; 60; 64], while continuous illumination was found favorable for EPS production in _Anabaena_ genus [54]. Much work has been done on _Nostoc flagelliforme_[11; 61; 63; 79; 80; 81; 82; 83; 84]. This strain is an edible terrestrial cyanobacteria that is used as food in China for more than 2000 years. The EPS from _N. flagelliforme_ are reported to be bioactive and possess interesting physico-chemical properties. Light quality experiments have shown that _N. flagelliforme_ has a higher growth rate and EPS production under monochromatic light, namely red and blue light when compared to white light [79; 80]. However, no relationship between monosaccharide composition and the quality of light applied was found [80]. The same was found for another _Nostoc_ sp. [85]. Culture medium optimization was found to enhance the antioxidant activity of CPS fraction [67]. Different light intensities of red light induced photoinhibition which possibly stimulated the protection of the cell by the production of EPS, namely CPS [80]. Optimization of carbon, nitrogen source, and light quality reinforced the fact that growth and EPS have their own requirements. In addition, these culture conditions also affected the EPS-associated enzymes, showing a correlation with the number of EPS produced [63]. More recently, a transcriptomic analysis revealed that light quality regulated EPS biosynthesis via the intracellular reactive oxygen species (ROS) level directly other than oxidative stress of _N.