Cyanobacteria isolated from the high-intertidal zone: a model for studying the physiological prerequisites for survival in low Earth orbit

AbstractCyanobacteria are capable of surviving the adverse conditions of low Earth orbit (LEO). We have previously demonstrated thatGloeocapsastrain OU_20,Chroococcidiopsisand akinetes ofAnabaena cylindricawere able to survive 548 days of exposure to LEO. Motivated by an interest to understand how cyanobacteria can survive in LEO, we studied the strategies thatGloeocapsastrain OU_20 employs to survive in its natural environment, the upper region of the intertidal zone. Here, cyanobacteria are exposed to fluctuations in temperature, UV radiation, desiccation and salinity. We demonstrated that an increase in salinity from 6.5‰ (BG-11 medium) to 35.7‰ (similar to that of seawater), resulted in increased resistance to UV radiation (254 nm), vacuum (0.7×10−3±0.01 kPa) and cold temperatures (–20 °C). Concomitantly, biochemical analyses demonstrated that the amount of fatty acids and mycosporine-like amino acids (a UV absorbing pigment) were higher in the stressed cells. Morphological analysis demonstrated that the electron density and thickness of the mucilaginous sheath were also greater than in the control cells. Yet, the control and stressed cells both formed aggregates. As a result of studying the physiological adaptation ofGloeocapsastrain OU_20 in response to salinity, we postulate that survival in the high-intertidal zone and LEO involves a dense extracellular mucilaginous sheath and the formation of aggregates. We conclude that studying the physiological adaptation of cyanobacteria in the intertidal zone provides insight into understanding survival in LEO.

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The affect of the space environment on the survival ofHalorubrum chaoviatorandSynechococcus(Nägeli): data from the Space Experiment OSMO on EXPOSE-R

International Journal of Astrobiology ◽

10.1017/s147355041400055x ◽

2014 ◽

Vol 14 (1) ◽

pp. 123-128 ◽

Cited By ~ 20

Author(s):

R. L. Mancinelli

Keyword(s):

Survival Rate ◽

Uv Radiation ◽

Molecular Probes ◽

Low Earth Orbit ◽

Space Environment ◽

Dust Particles ◽

Most Probable Number ◽

Earth Orbit ◽

Probable Number ◽

Space Vacuum

AbstractWe have shown using ESA's Biopan facility flown in Earth orbit that when exposed to the space environment for 2 weeks the survival rate ofSynechococcus(Nägeli), a halophilic cyanobacterium isolated from the evaporitic gypsum–halite crusts that form along the marine intertidal, andHalorubrum chaoviatora member of the Halobacteriaceae isolated from an evaporitic NaCl crystal obtained from a salt evaporation pond, were higher than all other test organisms exceptBacillusspores. These results led to the EXPOSE-R mission to extend and refine these experiments as part of the experimental package for the external platform space exposure facility on the ISS. The experiment was flown in February 2009 and the organisms were exposed to low-Earth orbit for nearly 2 years. Samples were either exposed to solar ultraviolet (UV)-radiation (λ > 110 nm or λ > 200 nm, cosmic radiation (dosage range 225–320 mGy), or kept in darkness shielded from solar UV-radiation. Half of each of the UV-radiation exposed samples and dark samples were exposed to space vacuum and half kept at 105pascals in argon. Duplicate samples were kept in the laboratory to serve as unexposed controls. Ground simulation control experiments were also performed. After retrieval, organism viability was tested using Molecular Probes Live–Dead Bac-Lite stain and by their reproduction capability. Samples kept in the dark, but exposed to space vacuum had a 90 ± 5% survival rate compared to the ground controls. Samples exposed to full UV-radiation for over a year were bleached and although results from Molecular Probes Live–Dead stain suggested ~10% survival, the data indicate that no survival was detected using cell growth and division using the most probable number method. Those samples exposed to attenuated UV-radiation exhibited limited survival. Results from of this study are relevant to understanding adaptation and evolution of life, the future of life beyond earth, the potential for interplanetary transfer of viable microbes via meteorites and dust particles as well as spacecraft, and the physiology of halophiles.

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