Cyanobacterial crust induction using two non-previously testedcyanobacterial inoculants: crusting capability and role of EPSs

The use of cyanobacteria as soil improvers and bio-conditioners (a technique often referred to as algalization) hasbeen studied for decades. Several studies proved that cyanobacteria are feasible eco-friendly candidates to triggersoil fertilization and enrichment from agricultural to arid and hyper-arid systems. This approach can be successfulto achieve stabilization and rehabilitation of degraded environments.Much of the effectiveness of algalization is due to the productivity and the characteristics of extracellularpolysaccharides (EPSs) which, among their features, embed soil particles and promote the development of a firststable organo-mineral layer (cyanobacterial crusts). In natural settings, cyanobacterial crust induction represents afirst step of a succession that may lead to the formation of mature biological soil crusts (Lan et al., 2014).The aim of this research was to investigate the crusting capabilities, and the characteristics of excreted EPSsby two newly tested non-heterocystous cyanobacterial inoculants, in microcosm experiments carried out usingoligothrophic sand collected from sand dunes in Negev Desert, Israel. The cyanobacteria tested were SchizothrixAMPL1601, originally isolated from biocrusts collected in Hobq Desert, Inner Mongolia (China) and Leptolyng-bia ohadii, originally isolated from biocrusts collected in Negev Desert, Israel.Inoculated microcosms were maintained at 30 ◦C in a growth chamber under continuous illumination and minimalwater availability. Under such stressing conditions, and for a three-months incubation time, the growth and thecolonization of the strains in the microcosms were monitored. At the same time, EPSs production and theirchemical and macromolecular characteristics were determined by applying a methodology optimized for thepurpose. Notably, EPSs were analyzed in two operationally-defined fractions, one more dispersed in the crustmatrix (loosely bound EPSs, LB-EPSs) and one more condensed and stable (tightly bound EPSs, TB-EPSs),which were deemed having different functions (Chen et al., 2014).The results demonstrated how differently (and complementarily in some ways) these two strains behave whenapplied on a poor sandy substrate, producing cyanobacterial crusts having different morphology. The outcomesof this study suggest the potential of Schizothrix AMPL1601 and Leptolyngbia ohadii as valid biotechnologicaltools for improving the properties of poor arid soils, allowing to design proper rehabilitation or restoration models.In addition, this study provided new insight on the characteristics of the cyanobacterial EPSs, secreted under aconstrained condition, compared to a non-nutrient limited and optimal one. Chen, L., Rossi, F., Deng, S., Liu, Y., Wang, G., Adessi, A., De Philippis, R., 2014. Macromolecular andchemical features of the excreted extracellular polysaccharides in induced biological soil crusts of different ages.Soil Biology and Biochemistry 78, 1–9. doi:10.1016/j.soilbio.2014.07.004 Lan, S., Zhang, Q., Wu, L., Liu, Y., Zhang, D., Hu, C., 2014. Artificially Accelerating the Reversal of Desertifica-tion: Cyanobacterial Inoculation Facilitates the Succession of Vegetation Communities. Environmental Science &Technology 48, 307–315. doi:10.1021/es403785j