Effect of nitrogen starvation on desiccation tolerance of Arctic Microcoleus strains (cyanobacteria).

Daria Tashyreva,Josef Elster

doi:10.3389/fmicb.2015.00278

Abstract

Although desiccation tolerance of Microcoleus species is a well-known phenomenon, there is very little information about their limits of desiccation tolerance in terms of cellular water content, the survival rate of their cells, and the environmental factors inducing their resistance to drying. We have discovered that three Microcoleus strains, isolated from terrestrial habitats of the High Arctic, survived extensive dehydration (to 0.23 g water g-1 dry mass), but did not tolerate complete desiccation (to 0.03 g water g-1 dry mass) regardless of pre-desiccation treatments. However, these treatments were critical for the survival of incomplete desiccation: cultures grown under optimal conditions failed to survive even incomplete desiccation; a low temperature enabled only 0–15% of cells to survive, while 39.8–65.9% of cells remained alive and intact after nitrogen starvation. Unlike Nostoc, which co-exists with Microcoleus in Arctic terrestrial habitats, Microcoleus strains are not truly anhydrobiotic and do not possess constitutive desiccation tolerance. Instead, it seems that the survival strategy of Microcoleus in periodically dry habitats involves avoidance of complete desiccation, but tolerance to milder desiccation stress, which is induced by suboptimal conditions (e.g., nitrogen starvation).

Highlights

Terrestrial cyanobacteria are often considered to be desiccation tolerant organisms
Cyanobacterial Strains The experiments were conducted with strains Microcoleus sp. 816 CCALA isolated from a stream in the vicinity of a glacial moraine (Northern Sweden, Lapland, Abisko, 69◦21 N 18◦49 E); Microcoleus vaginatus 858 CCALA isolated from a small pool in a moraine (Svalbard archipelago, 77◦00 N 15◦20 E); and Microcoleus sp. 845 CCALA isolated from a stream with moss carpets (Svalbard archipelago, 77◦00 N 15◦20 E)
All experiments were run in triplicate, i.e., pre-cultivation and cultivation in biofilms, subsequent predesiccation treatments, desiccation at both regimes, and viability tests were run three times separately for each of the strains

Summary

Introduction

Terrestrial cyanobacteria are often considered to be desiccation tolerant organisms. Some taxa of cyanobacteria have evolved a remarkable ability to resist desiccation stress (Caiola et al, 1996; Potts, 1999). Most of the studies evaluated the survival and stress response of Phormidium and Microcoleus at the population level, e.g., ‘bulk’ measurement of respiration/photosynthesis measured by oxygen evolution/uptake, recovery of photosynthesis, or growth tests (Davey, 1989; Hawes et al, 1992; Chen et al, 2003; Harel et al, 2004; Šabacká and Elster, 2006; Rajeev et al, 2013). Such an approach often overlooks the number of cells that survive and their physiological state upon rehydration. We endeavored to determine: (1) whether desiccation tolerance is a constitutive property or if it is inducible by suboptimal conditions, i.e., low temperature and nitrogen depletion, (2) whether the strains are able to tolerate complete desiccation defined as water content below 0.1 g H2O g−1 dry biomass (Alpert, 2005) and/or incomplete (85% RH) desiccation regimes, and (3) which proportion of cells survives desiccation and what their physiological state upon rehydration is

Materials and Methods

Results

Discussion