Exopolysaccharide Features Influence Growth Success in Biocrust-forming Cyanobacteria, Moving From Liquid Culture to Sand Microcosms

Sonia Chamizo; Alessandra Adessi; Giuseppe Torzillo; Roberto De Philippis

doi:10.3389/fmicb.2020.568224

Exopolysaccharide Features Influence Growth Success in Biocrust-forming Cyanobacteria, Moving From Liquid Culture to Sand Microcosms

Front Microbiol. 2020 Oct 27:11:568224. doi: 10.3389/fmicb.2020.568224. eCollection 2020.

Authors

Sonia Chamizo^{1

2}, Alessandra Adessi³, Giuseppe Torzillo^{4

5}, Roberto De Philippis³

Affiliations

¹ Department of Agronomy, University of Almería, Almería, Spain.
² Research Centre for Scientific Collections from the University of Almería (CECOUAL), Almería, Spain.
³ Department of Agriculture, Food, Environment and Forestry (DAGRI), University of Florence, Firenze, Italy.
⁴ CNR -Institute of BioEconomy, Sesto Fiorentino, Italy.
⁵ Centro de Investigación en Ciencias del Mar y Limnología, Universidad de Costa Rica, San José, Costa Rica.

Abstract

Land degradation in drylands is a drawback of the combined action of climate change and human activities. New techniques have been developed to induce artificial biocrusts formation as a tool for restoration of degraded drylands, and among them soils inoculation with cyanobacteria adapted to environmental stress. Improvement of soil properties by cyanobacteria inoculation is largely related to their ability to synthesize exopolysaccharides (EPS). However, cyanobacterial EPS features [amount, molecular weight (MW), composition] can change from one species to another or when grown in different conditions. We investigated the differences in growth and polysaccharidic matrix features among three common biocrust-forming cyanobacteria (Nostoc commune, Scytonema javanicum, and Phormidium ambiguum), when grown in liquid media and on sandy soil microcosms under optimal nutrient and water, in controlled laboratory conditions. We extracted and analyzed the released EPS (RPS) and sheath for the liquid cultures, and the more soluble or loosely-bound (LB) and the more condensed or tightly-bound (TB) soil EPS fractions for the sandy soil microcosms. In liquid culture, P. ambiguum showed the greatest growth and EPS release. In contrast, on the sandy soil, S. javanicum showed the highest growth and highest LB-EPS content. N. commune showed no relevant growth after its inoculation of the sandy soil. A difference was observed in terms of MW distribution, showing that the higher MW of the polymers produced by P. ambiguum and S. javanicum compared to the polymers produced by N. commune, could have had a positive effect on growth for the first two organisms when inoculated on the sandy soil. We also observed how both RPS and sheath fractions reflected in the composition of the soil TB-EPS fraction, indicating the role in soil stabilization of both the released and the cell attached EPS. Our results indicate that the features of the polysaccharidic matrix produced by different cyanobacteria can influence their growth success in soil. These results are of great relevance when selecting suitable candidates for large-scale cyanobacteria applications in soil restoration.

Keywords: EPS molecular weight distribution; EPS monosaccharidic composition; cyanobacteria liquid culture; sand inoculation; sandy soil microcosms; semiarid soil.