**5. Conclusions**

The present work provided important indications regarding the defense mechanisms of two cyanobacteria, namely, *P. ambiguum* and *L. ohadii,* to water deprivation in biocrusts and in biofilm formation. The strains showed EPS synthesis capability even in water deprived conditions, demonstrating a distinct production pattern of EPS. Particularly the production of TB-EPS was significantly increased in biocrusts after the water deprivation, suggesting the importance of this fraction in slowing down desiccation. In biofilms under water deprivation, the sheath EPS was significantly more abundant than the RPSs and G-EPS, suggesting that it may perform a crucial role in stress tolerance. The different profile of monosaccharidic composition demonstrated the plasticity of the cells to modify EPS in order to respond different stresses, as reported here by the higher concentration of deoxysugars in biocrusts compared to biofilms. For the two cyanobacteria evaluated in this work, waterdeprived biofilms and biocrusts tend to produce simpler carbohydrates and increase their dominance index. The knowledge of different cyanobacteria biological mechanisms to cope with harsh environmental conditions is important to select the best strain for the use in the restoration of dryland soils and the improvement of ecosystems services.

**Supplementary Materials:** The following supporting information can be downloaded at: https: //www.mdpi.com/article/10.3390/polym15081889/s1, Figure S1: biocrusts and biofilms control and water deprived; Figure S2: biocrust features after 4 weeks watered; Figure S3: LB-EPS and TB-EPS contents ; Figure S4: biofilm features after 4 weeks with culture medium; Figure S5: RPS, sheath and G-EPS contents; Table S1: diversity indices of the biocrusts EPS; Table S2: diversity indices of the biofilms EPS; Table S3: sugar total mols and mols of each monosaccharide in each EPS fraction for *P. ambiguum* biocrusts; Table S4: sugar total mols and mols of each monosaccharide in each EPS fraction for *L. ohadii* biocrusts; Table S5: sugar total mols and mols of each monosaccharide in each EPS fraction for *P. ambiguum* biofilms; Table S6: sugar total mols and mols of each monosaccharide in each EPS fraction for *L. ohadii* biofilms.

**Author Contributions:** Conceptualization, I.C.M. and A.A.; methodology, I.C.M., A.A., S.B.P. and P.D.; formal analysis, I.C.M.; writing—original draft preparation, I.C.M.; writing—review and editing, A.A., S.B.P., P.D. and R.D.P.; supervision, R.D.P. and A.A. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research received no external funding.

**Institutional Review Board Statement:** Not applicable.

**Data Availability Statement:** Not applicable.

**Conflicts of Interest:** The authors declare no conflict of interest.
