# Exopolysaccharides from Cyanobacteria: Strategies for Bioprocess Development
## 3 Cyanobacterial Bioprocess (Cyano-EPS) Development
### Downstream Processes and Cyano-EPS Global Market  
Interest for cyanobacteria EPS has increased significantly during the last two decades as they offer some structural originalities compared to those extracted from marine microalgae and to hydrocolloids from macroalgae and plants [10; 50]. They have wide putative applications such as: food additives, soil (water holding capacity), wastewater treatments (removal of heavy metals), bioactive agents for nutraceutical, pharmaceutical, and cosmetic fields [101]. The development of strategies for their extraction and purification is strongly correlated with their cellular location. EPS should be employed only to reference polysaccharides excreted by microorganisms in their extracellular environment and not having covalent links with their cellular envelope. Considering the abundant literature focusing on polysaccharides from cyanobacteria they can be divided into three groups: biopolymers poorly associated with the cell surface and usually encompassed under the term of slime or released polysaccharides (RPS); polysaccharide structured as a sheath, which is a thin layer next to the outer cell membrane and containing fibers; capsular polysaccharides (CPS) intimately associated with the envelope cells [102]. The extraction and purification of these polysaccharides from cyanobacterial culture media is a major concern before the investigation of their structure and/or to find commercial applications. The main question before developing a strategy for their purification is what kind of EPS is the objective of the extraction: slime, sheath, or capsular polysaccharides? Several articles or reviews detail the processes available for the extraction of these three kinds of biopolymers, often calling them with different appellations, increasing the confusion between these different classes [102; 103; 104; 105; 35; 40]. All the protocols are summarized in Figure 1. Firstly, the extracellular medium of cyanobacteria  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Strains**} & \multicolumn{3}{c}{**Optimization Factor**} & \multicolumn{2}{c}{**EPS Tite/Productivity**} \\ \cline{2-5}  & **Culture Media** & **Process Parameters** & **/Field** & **Literature** \\ \hline \multirow{2}{*}{_Cyanothelec_ _eptiolytica_} & N source (**absence**; NaNO\({}_{3}\)); & & & \\  & **Culture Media** & **Process Parameters** & **/Field** & **Literature** \\ \hline \multirow{2}{*}{_Cyanothelec_ _eptiolytica_} & N source (**absence**; NaNO\({}_{3}\)); & & & \\  & **Saliinity (NaCI)**; & & & \\  & **Saliinity (NaCI)**; & & & \\  & **Saliinity (NaCI)**; & & & \\  & **Cyanothelec sp. CCY & (absence/  
cultures is collected generally by centrifugation, but tangential microfiltration may be an interesting alternative as described by [106] for red microalgae or by [10]. Note that [105] suggested suspending the pellet in Milli-Q water and to incubate them at 4 \({}^{\circ}\)C during 12 h before to centrifuge them again to collect, by depletion, the maximum of slime. The cyanobacteria free supernatants or permeates are then treated by polar alcohols (methanol, ethanol, or isopropanol) or acetone to precipitate the EPS. The volume ratios are different depending on studies but two or three volumes of cold ethanol (or isopropanol) is probably a good compromise. Sometimes the supernatant is concentrated under vacuum at low temperatures (50-60 \({}^{\circ}\)C) to limit the volume of used alcohol or acetone [10; 50]. This sole EPS precipitation is generally not enough to remove salts and/or low molecular weight metabolites from extracted polysaccharides as they co-precipitated during alcohol/acetone treatment. So, two protocols are generally used by authors to increase the purity level of polysaccharides, measured by Dubois assay [107]. The first one is a solubilization of dried polysaccharides in Milli-Q water before their precipitation using the same alcohol or acetone volume ratio. The second one is to dialyze them against water. Finally, the EPS are freeze-dried or dried under vacuum.