After their return from the ISS almost all samples developed into new populations. The green alga (top 2 rows) also developed orange-coloured resting stages, whilst typically blue-green pigmented colonies were developed by the cyanobacterium (bottom 2 rows).

The many different organisms from all participating partners were all mounted in such trays and then exposed to space on the outside of the ISS for one and a half years.

They’re alive! Two algae survived 16 months on the exterior of the International Space Station ISS despite extreme temperature fluctuations and the vacuum of space as well as considerable UV and cosmic radiation. That was the astonishing result of an experiment conducted by Dr. Thomas Leya at the Fraunhofer Institute for Cell Therapy and Immunology IZI in Potsdam in cooperation with German and international partners. This labor-intensive experiment was part of the large-scale Biology and Mars Experiment (BIOMEX), a project coordinated by Dr. Jean-Pierre de Vera at the German Aerospace Center (DLR) in Berlin. Dr. Leya himself had isolated the green algal strain CCCryo 101-99 of Sphaerocystis sp. on Svalbard, a Norwegian archipelago, and prepared it together with the cyanobacterium Nostoc sp. (CCCryo 231-06), a blue-green alga from Antarctica. CCCryo stands for Culture Collection of Cryophilic Algae. Nostoc sp. and Sphaerocystis sp. are examples of cold-loving, or cryophilic, strains. They have special adaptation strategies to oppose cold and desiccation, allowing them to survive even under extreme conditions.

Dr. Leya heads the Extremophile Research & Biobank CCCryo Working Group at Fraunhofer’s Bioanalytics and Bioprocesses IZI-BB branch in Potsdam. For the past 18 years, the group has been studying the survival strategies of cryophilic algae, cyanobacteria, mosses, fungi and bacteria found in polar regions. Researchers had already ascertained in the laboratory that algae are largely unsusceptible to long-term desiccaton stress, extreme temperatures or UV radiation. Yet the extreme conditions of near-Earth orbit cannot be fully simulated in labs.

“We slightly desiccated the algal strains in preparation for their time in space,” explains Dr. Leya. A Progress spacecraft transported the organisms into space on July 23, 2014, and a Soyuz capsule returned the algal cultures to Earth. All in all, they had to endure some 16 months on the outside of the ISS – with only neutral-density filters reducing the effects of radiation. Sensors measured and logged temperature changes and amounts of cosmic radiation.