Crucial Role of Extracellular Polysaccharides in Desiccation and Freezing Tolerance in the Terrestrial Cyanobacterium Nostoc commune

Abstract

The cyanobacterium Nostoc commune is adapted to the terrestrial environment and has a cosmopolitan distribution. In this study, the role of extracellular polysaccharides (EPS) in the desiccation tolerance of photosynthesis in N. commune was examined. Although photosynthetic O 2 evolution was not detected in desiccated colonies, the ability of the cells to evolve O 2 rapidly recovered after rehydration. The air-dried colonies contained approximately 10% (wt/wt) water, and field-isolated, natural colonies with EPS were highly water absorbent and were rapidly hydrated by atmospheric moisture. The cells embedded in EPS in Nostoc colonies were highly desiccation tolerant, and O 2 evolution was not damaged by air drying. Although N. commune was determined to be a mesophilic cyanobacterium, the cells with EPS were heat tolerant in a desiccated state. EPS could be removed from cells by homogenizing colonies with a blender and filtering with coarse filter paper. This treatment to remove EPS did not damage Nostoc cells or their ability to evolve O 2 , but O 2 evolution was significantly damaged by desiccation treatment of the EPS-depleted cells. Similar to the EPS-depleted cells, the laboratory culture strain KU002 had only small amount of EPS and was highly sensitive to desiccation. In the EPS-depleted cells, O 2 evolution was also sensitive to freeze-thaw treatment. These results strongly suggest that EPS of N. commune is crucial for the stress tolerance of photosynthesis during desiccation and during freezing and thawing.

Desiccation induced changes in osmolytes production and the antioxidative defence in the cyanobacterium Anabaena sp. PCC 7120

“…PCC 7120 cells desiccated for 1 h seemed to be interlinked. Reduced O 2 evolution during 1 h of desiccation and an increased Chl a content are in line with those reported for Nostoc commune (Tamaru et al 2005). Phycocyanin is the predominant energy collectors of PS II, and once degraded, energy transfer to PSII gets impaired, as can be evident from decreased O 2 evolution in present study.…”

“…Cyanobacterial cells were desiccated for pre-determined durations and the dried biomass (10 mg) used to measure oxygen evolution as described by Tamaru et al (2005). Rehydration of biomass was done in an oxygen electrode chamber (Rank Brothers, Cambridge, U. K.) with 25 mM HEPES-NaOH buffer (pH 7.0) supplemented with 10 mM NaHCO 3 .…”

Cyanobacterial metabolites as a source of sunscreens and moisturizers: a comparison with current synthetic compounds

“…Cyanobacteria such as Chroococcidiopsis and Nostoc species are able to survive with minimal water by synthesizing both internal and external polysaccharides (Warren-Rhodes et al, 2013;Smith et al, 2014). Tamaru et al (2005) indicated that the desiccation tolerance of Nostoc commune is strongly associated with extracellular polymeric substances (EPS). They removed the EPS from N. commune cells by homogenizing colonies with a blender and filtering through a coarse filter paper, and showed that cells depleted in EPS were highly sensitive to desiccation.…”

“…They removed the EPS from N. commune cells by homogenizing colonies with a blender and filtering through a coarse filter paper, and showed that cells depleted in EPS were highly sensitive to desiccation. The hydrophilic/hydrophobic characteristics of EPS enable it to trap and accumulate water, and retard water loss during periods of desiccation (Tamaru et al, 2005). Li et al (2011) showed that Nostoc commune EPS has strong moisture-absorption and retention capacities compared with chitosan (a hygroscopic agent) and urea (a humectant).…”

Mutations Stabilize Small Subunit Ribosomal RNA in Desiccation-Tolerant Cyanobacteria Nostoc

“…Nostoc cells experience extremes of desiccation, of which the water content is 0.02 to 0.05 g water cell solid -1 , approximately one order of magnitude lower than that of eubacterial spores (0.21 to 0.58) [27]. The mechanisms involved in the desiccation tolerance of Nostoc have been investigated using ecophysiology, biochemistry, and molecular biology [13,30,31,36]. However, the stability and biophysical properties of macromolecules inside desiccated cells are still poorly understood.…”