PLANT AND MICROBIAL RESEARCH

Plant and microbial research on the ISS fulfills two major goals: (1) to increase basic knowledge of how these organisms sense and respond to their environment, especially gravity-related phenomena, and (2) to provide the underpinning for enabling sustained human habitation in space.

There has not been a comprehensive program dedicated to analyzing microbial populations and responses to spaceflight. This represents a critical gap in our knowledge because microbial populations play significant roles in positive and negative aspects of human health and in the degradation of their environment through, for example, food spoilage and biofouling of equipment. At present there is little information on how long-term contact with the combination of factors imposed during spaceflight, such as chronic exposure to cosmic radiation and altered physical parameters associated with microgravity such as reduced convection, could lead to changes in microbial populations or provide sufficient selective pressures to drive microbial evolutionary processes. Also, the degree to which such changes reflect physiological responses to the spaceflight environment versus genomic changes remains undefined. Continued access to the ISS coupled to the technological maturity, low cost, and speed of genomic analyses, plus the rapid generation time of microbes, makes monitoring of the evolution of microbial genomic changes induced by extended growth in space a highly feasible short-term goal. Since samples could be taken from the surfaces of the ISS and the crew on board and returned for analysis on the ground, the on-orbit portion of this research could largely be accomplished using the already-existing microbial air and surface sampler kits. This research would allow a comprehensive analysis of microbial population changes in response to the factors present in the spaceflight environment that impact the rates of reproduction or survival of microbes, using both experimentally established populations and samples of microbes colonizing the surfaces and the crew of the ISS.

In contrast, a series of experiments on the ISS with a focus on plants has provided an initial, limited characterization of plant responses ranging from the developmental and molecular changes elicited by spaceflight to changes in photosynthesis, phototropism, and gravisensing in this environment.1,2

One aim of this research has been to acquire basic knowledge to enable the use of plants for long-term life support in extraterrestrial habitats by capitalizing on plants’ ability to provide fresh food and to aid in the recycling of air, water, and waste products. Establishing the robust elements of such a bioregenerative life support system, which will likely incorporate a combination of biological systems and physico-chemical technologies, requires extended research now that carefully integrates ground- and ISS-based work. Levels and quality of light, atmospheric composition, nutrient levels, and availability of water are all critical elements shaping plant growth in space, where each needs to be optimized in a rigorously tested technology platform designed to maximize plant performance during spaceflight. Although such a research program will be enabled by access to the unique environment of the ISS, it is fundamentally aimed at enabling the long-term human presence in space. Developing a sustained research program combining ground- and ISS-based design and validation of components will be critical to establishing the dynamic integrated intramural and extramural research community necessary to support this area. Food plants will be a cornerstone of this effort because they alone can synthesize nutritious, edible biomass from carbon dioxide (CO2), inorganic nutrients, and water while revitalizing the atmosphere using the energy of light. However, microbial reactors will likewise require attention to ensure that they can reliably and efficiently process the solid, liquid, and gaseous wastes of habitation. The ISS provides a key enabling resource for beginning to test the efficacy of each component of a long-

1

C. Wolverton and J.Z. Kiss, An update on plant space biology, Gravitational and Space Biology 22(2):13-20, 2009.

2

C.A. Evans, J.A. Robinson, J. Tate-Brown, T. Thumm, J. Crespo-Riche, D. Baumann, and J. Rhatigan, International Space Station Science Research Accomplishments during the Assembly Years: An Analysis of Results from 2000-2008, NASA/TP-2009-213146–Revision A, NASA, Washington, D.C., 2009.



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