# Cyanobacterial Potential for Restoration of Loess Surfaces through Artificially Induced Biocrusts
## 4 Discussion
### Production of Toxin, Biomass and Polysaccharide by the Cyanobacterial Strains
#### 4.1.3 Production of Polysaccharides  
The presence of nitrogen can influence the EPS production summarized in [65, 97], which does not necessarily follow the pattern of biomass production, as observed in this study (Table 3). The lowest yield of total polysaccharides was observed in _Nostoc_ sp. L5 with the highest biomass production after seven weeks of cultivation in BG11 N+ medium. The highest yield of total polysaccharides was observed in _Chroococcidipsis_ sp. L1 strain cultivated in BG11 N\(-\) medium. Nevertheless, even in the stationary phase, the strain had one of the lowest observed biomass (Table 2). A few studies have shown that EPS production is enhanced upon entering the stationary growth phase [66, 98, 99], which could explain the higher total polysaccharide yield by our strain. In addition, _Chroococcidipsis_ strains can produce larger amounts of capsular polysaccharides when exposed to nitrogen deficiency [95], to create microaerobic conditions and protect the enzyme nitrogenase from being inactivated by O\({}_{2}\)[96]. Statistical analyses (Table 4) further verified that the medium composition has an influence on the polysaccharide production in the analyzed strains.  
For most of the strains, the RPS yield was in a positive correlation with the total polysaccharide yield, which indicates the importance of N in RPS synthesis. The RPS yields observed in this study (Table 3) are generally in agreement with the values observed by [PERSON] et al. [100], even though their strains were cultivated under different cultivationconditions: permanent light, higher temperatures, aeration, and mechanical agitation. Numerous studies showed that permanent light duration and intensity, higher temperatures and aeration could significantly enhance the production of RPSs [98, 101, 102, 103], thus further optimization of cultivation conditions could result in a higher RPS yield than observed in this study.  
The production of RPS in cultures causes a progressive increase in medium viscosity [66]. The viscosity of the cell-free medium examined in this study did not show a strict positive correlation with the yield of RPSs produced. The highest viscosity was observed in BG11 N+ medium of the strain _Chroococcidopsis_ sp. L1, although the yield of RPSs produced by this strain was significantly higher when cultivated in BG11 N\(-\) medium. The high viscosity of the cell-free medium of another strain, _Nostoc_ sp. L5, was observed, although the strain had the lowest yield of RPSs among all examined strains. In contrast, the lowest viscosity of the cell-free medium was measured in the strain _Nostoc_ sp. L6 cultivated in BG11 N+ medium, which had the second-highest RPS yield. The observed results suggest that it may not be the amount of RPSs produced that play a critical role in a medium viscosity, but their structure. [PERSON] and [PERSON] [104] showed that polysaccharides of higher molecular weights and of the more linear structure have a higher viscosity, and cyanobacteria are known to produce exopolysaccharides of high molecular weights [97]. Viscosity is also affected by the presence of charged groups and the presence of protein moieties in the RPS structure [66]. Thus, even though the RPS yield was lower, the quality of RPSs in terms of molecular weight, monosaccharide content, and abundance of charged groups and proteins in their structure might have contributed to viscosity. The statistical analysis (Table 4) showed no statistically significant influence of the media composition on the viscosity, indicating that the structure of the produced polysaccharides, which is primarily a genetic characteristic of the production strain, contributes to the increase of the viscosity of the medium.