## 6 Methods for Obtaining Selenium-Containing Polysaccharides
### Biotechnological Methods  
When considering the biotechnological methods to obtain Se-polysaccharides, the cultures of plants, fungi, algae, or microorganisms are grown in media enriched with soluble selenium compounds. The culture is then used to isolate selenium-enriched polysaccharide fractions from the selenium-enriched biomass of the cultivated species (cell wall polysaccharides and endo-polysaccharides) or from the culture medium (exo-polysaccharides). In order to isolate and purify Se-polysaccharides from those cultured organisms, the methods used are the same as for other natural sources. As a result of the transport into the cell and following enzymatic processes, selenium compounds supplementing the medium may be incorporated into the structure of polysaccharides, as happens with plants or fungi grown on substrates enriched with selenium compounds. However, the biotechnological methods are in many aspects advantageous over the crops cultivation [331].  
A major advantage is the shorter time of cultivation in bioreactors, which gives a significant reduction in the time needed to obtain a comparable biomass. Moreover, culturing in bioreactors is carried out under repeatable conditions, resulting in a stable composition of the grown biomass. This facilitates standardization of the preparations, for example for pharmaceutical use.  
Biotechnological processes also use optimized composition of the culture media and physico-chemical conditions of the culture. This enables regulation of the metabolism of the cultivated organism and results in a significant increase in efficiency of the biologically active compounds. Finally, the technology of the biotechnological processes provides monitoring and maintenance of the biochemical and genetic identity of the strain cultivated in a fermenter.  
However, there are also serious disadvantages of using of modern biotechnological methods when compared with crops cultivation or hydroponics. Primarily, not all species of plants and fungi are capable of growing as efficiently as cell, callus, or mycelial cultures in bioreactors. Moreover, the cultivation of plants (cell, callus, or tissue cultures) and higher fungi (mostly mycelial cultures) in bioreactors faces more challenges than the culture of single-celled organisms. Additionally, the use of biotechnological methods is mostly more expensive than crops. When using biotechnological methods of cultivation, the costs of specialized equipment and apparatus, energy, the required specific constituents of the culture media, highly specialized service, maintaining sterile conditions, etc., are relatively high. However, in the case of protected plants or fungi, plants growing slowly in crops, or hydroponic cultivation, coming from climatic zones/regions, where cropping is very difficult, the choice of the biotechnological methods is favorable. Biotechnological cultures of ginseng (_Panax ginseng_ [PERSON]) are a good example. Field cultivation of _Panax ginseng_ is a slow and laborious process; therefore, cell and tissue culture methods have been explored as potentially more efficient for ginseng biomass and its bioactive components production [332]. Regardless, the decisive factors in choosing the method of obtaining biological material, for example, for the polysaccharide isolation, are its implementability and of course the cost.  
A great number of reports have been published on the preparation of Se-polysaccharides (exo- and endo-polysaccharides) by biotechnological methods. Only a few examples will be given below.  
Selenium-containing polysaccharides were isolated from cultures of fungi, e.g., liquid cultures of _Hericium erinaceum_[13], stillage from _Cordyceps sinensis_[108], mycelia of _Catalhesima ventricosum_[246], _Poria cocos_ mycelia [247], mycelium of _Pholiota dinglunensis_[248] and _Lentinula edodes_[249], _Pleutrotus geseteranus_[333], and other microorganisms, such as _Spirulina platensis_[251], _Enterobacter cloacae_[250], _Pseudomonas_ sp. [334], _Leuconstoc mesenteroides_[335], and many others.