Hardening Stenomitos frigidus ULC029 by applying sequential stress factors

Soil degradation in warm drylands is increasing due to land-use intensification. To restore these soils, we need to develop technologies that are efficient under the extreme environmental con ditions in drylands. One strategy is the inoculation of cyanobacteria to restore soil biocrusts, be cause these communities provide multiple benefits to the ecosystem. However, after extended laboratory culturing, the cyanobacteria need to be re-adapted to natural conditions to optimize their survival, even if they were shown to be resistant to extreme stress when isolated. Here, we analyzed the genome and ecophysiological response to sequential stresses (osmotic, desicca tion and UVR) of an Antarctic cyanobacterium, Stenomitos frigidus ULC029. Chlorophyll a con centrations show that preculturing ULC029 under moderate osmotic stress improved its survival
during an assay of desiccation plus rehydration under UVR. Additionally, its sequential exposure to these stress factors increased the production of exopolysaccharides, carotenoids and scytone min. Desiccation, but not osmotic stress, increased the concentrations of the osmoprotectants, trehalose and sucrose. However, osmotic stress might induce the production of other osmopro tectants, for which the complete pathways were found in its genome. Here, we confirm that the sequential application of moderate osmotic stress and dehydration, could improve cyanobacterial hardening for soil restoration, by inducing several resistance mechanisms