Effect of inoculated cyanobacteria on the structure and development of inducedbiological soil crust

Cyanobacteria are feasible eco-friendly candidates to trigger soil improvement andenrichment. According to several studies, cyanobacteria could be employed as inoculants in differentcontexts, from agricultural to arid and hyper-arid systems. Successful soil inoculation withcyanobacteria leads to the development of cyanobacterial crusts, which are recognized as the firstlevel of development of biological soil crusts, the latter being a key natural and ecologicallyfundamental component in many stressed ecosystems on Earth. Much of the success as inoculants isowed to the productivity and the characteristics of extracellular polysaccharides (EPSs) which arecomplex heteropolymers, which contribute to soil conglomeration and biolayer stability. In order toinvestigate the role of EPSs in cyanobacterial crust development during the first stages of the process,we employed different strains isolated from natural desert biological soil crusts and inoculated them,alone or combined, on fine sand in a microcosm (indoor) experiment. Besides monitoring the growthparameters and the development of the crusts, we evaluated EPS productivity during developmentand we investigated their composition and molecular weight distribution using ion-exchangechromatography and size-exclusion chromatography. Both loosely-bound (less condensed) andtightly-bound EPS fractions were considered in the investigation. In addition, some soil chemo-physical and hydrology-related soil parameters potentially affected by EPS excretion were monitored,at regular intervals, during crust development. The results obtained showed how the use of theselected strains led to the development of stable cyanobacterial crusts in very short times. This study prominently points out at the paramount role of EPSs in determining the observed variations in someof the parameters observed during the experiment duration.