Survival of akinetes (resting-state cells of cyanobacteria) in low earth orbit and simulated extraterrestrial conditions.

Cyanobacteria are photosynthetic organisms that have been considered for space applications, such as oxygen production in bioregenerative life support systems, and can be used as a model organism for understanding microbial survival in space. Akinetes are resting-state cells of cyanobacteria that are produced by certain genera of heterocystous cyanobacteria to survive extreme environmental conditions. Although they are similar in nature to endospores, there have been no investigations into the survival of akinetes in extraterrestrial environments. The aim of this work was to examine the survival of akinetes from Anabaena cylindrica in simulated extraterrestrial conditions and in Low Earth Orbit (LEO). Akinetes were dried onto limestone rocks and sent into LEO for 10 days on the ESA Biopan VI. In ground-based experiments, the rocks were exposed to periods of desiccation, vacuum (0.7×10(-3) kPa), temperature extremes (-80 to 80°C), Mars conditions (-27°C, 0.8 kPa, CO(2)) and UV radiation (325-400 nm). A proportion of the akinete population was able to survive a period of 10 days in LEO and 28 days in Mars simulated conditions, when the rocks were not subjected to UV radiation. Furthermore, the akinetes were able to survive 28 days of exposure to desiccation and low temperature with high viability remaining. Yet long periods of vacuum and high temperature were lethal to the akinetes. This work shows that akinetes are extreme-tolerating states of cyanobacteria that have a practical use in space applications and yield new insight into the survival of microbial resting-state cells in space conditions.

Physiological and biochemical alterations in a diazotrophic cyanobacterium Anabaena cylindrica under NaCl stress.

Growth, morphological variation, and liquid chromatography-photodiode array detection-mass spectrometric analysis of pigments have been studied in a diazotrophic cyanobacterium Anabaena cylindrica in response to NaCl stress. The chlorophyll and cellular protein contents increased initially in response to 50 mM: NaCl. Further increment in NaCl concentration, however, resulted in a significant decrease in both chlorophyll and cellular protein. A. cylindrica cells subjected to NaCl stress also showed morphological variations by having alteration in their size and volume. A. cylindrica cells subjected to NaCl stress also exhibited altered plastoquinone and chlorophyll-a (chl a) levels in comparison to its NaCl-untreated counterpart. Furthermore, a relative increase in plastoquinone level and a subsequent decrease in chl a level were recorded in NaCl adapted cells of A. cylindrica in response to NaCl stress. These results suggest that owing to adaptation various morphological, physiological, and biochemical changes occur in the cyanobacterium A. cylindrica in response to NaCl stress.