The O/OREOS Mission: First Science Data from the Space Environment Survivability of Living Organisms (SESLO) Payload

Abstract

We report the first telemetered spaceflight science results from the orbiting Space Environment Survivability of Living Organisms (SESLO) experiment, executed by one of the two 10 cm cube-format payloads aboard the 5.5 kg Organism/Organic Exposure to Orbital Stresses (O/OREOS) free-flying nanosatellite. The O/OREOS spacecraft was launched successfully to a 72° inclination, 650 km Earth orbit on 19 November 2010. This satellite provides access to the radiation environment of space in relatively weak regions of Earth's protective magnetosphere as it passes close to the north and south magnetic poles; the total dose rate is about 15 times that in the orbit of the International Space Station. The SESLO experiment measures the long-term survival, germination, and growth responses, including metabolic activity, of Bacillus subtilis spores exposed to the microgravity, ionizing radiation, and heavy-ion bombardment of its high-inclination orbit. Six microwells containing wild-type (168) and six more containing radiation-sensitive mutant (WN1087) strains of dried B. subtilis spores were rehydrated with nutrient medium after 14 days in space to allow the spores to germinate and grow. Similarly, the same distribution of organisms in a different set of microwells was rehydrated with nutrient medium after 97 days in space. The nutrient medium included the redox dye Alamar blue, which changes color in response to cellular metabolic activity. Three-color transmitted intensity measurements of all microwells were telemetered to Earth within days of each of the 48 h growth experiments. We report here on the evaluation and interpretation of these spaceflight data in comparison to delayed-synchronous laboratory ground control experiments.

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“…Non-motile cells in near-weightlessness, in unagitated culture, generally grow or metabolize more slowly than those subjected to Earth gravity due to the absence of gravitationally driven thermal convection and, indeed, the SESLO experiments showed that B. subtilis had slower metabolism and growth in near-weightlessness than those in an identical control experiment on Earth. Surprisingly, the mutant strains metabolized more rapidly than the wild-type in near-weightlessness (Nicholson et al 2011). …”

“…Two B. subtilis strains were studied: a wild-type form of strain 168 and an ionizing-radiation-sensitive strain (WN1087) with a mutation that effects its DNA repair system; it is otherwise identical to the wild-type form (Nicholson et al 2011). Both strains were deposited as spores in microwells of the SELSO payload.…”

“…7). Research in low Earth orbit has contributed to our knowledge on extraterrestrial delivery processes, the responses of life to the space environment and crucial aspects of planetary protection (Guan et al 2010;Nicholson et al 2011). Some of the main facilities used both for chemical and biological applications are described in this section.…”

“…Prior to spacecraft integration and flight, bacterial cells were dried onto the walls of the sample wells and the bioblocks were sealed using a gas-permeable membrane. Using 3-color LED illumination (470, 525, and 615 nm), the growth and metabolism of the microbe Bacillus subtilis was successfully measured during the mission at 2 weeks, 3 months and 6 months after launch (Nicholson et al 2011). Results are summarized below in "O/OREOS Results" (Sect.…”

“…The Space Environment Survivability of Living Organisms (SESLO) experiment collected data on the survival and metabolic activity of microbes at 3 times during the 6-month mission (Nicholson et al 2011): t = 2 weeks, 3 months, and 6 months after orbital deployment. The biological payload includes three "bioblock" modules, one per measurement time point.…”