© N.Leys, C.Paille
© Государственный музей истории космонавтики им. К.Э. Циолковского, г. Калуга
Секция "К.Э. Циолковский и проблемы космической медицины и биологии"
2008 г.

A closed regenerative life support system for manned bases on the Moon or Mars cannot be conceived without biological processes. Microbes are essential for human well-being, for waste and water recycling, oxygen and food production. The «MELiSSA» system, is a regenerative life support system under development by ESA to support a human life in space based on bacterial waste recycling in which 4 bacterial compartments play a key role. In the first compartment, the bacterium such as Clostridium thermocellum are needed to degrade organic polymer fibers (e.g. cellulose) in smaller organic compounds. The purple non-sulfur α-proteobacterium Rhodospirillum rubrum S1H is a key organism in the second «MELiSSA» compartment to convert anaerobically (no consumption of oxygen) organic compounds (volatile fatty acids VFA) to carbon dioxide. Nitrosomonas and Nitrobacter are responsible for the conversion of nitrate to nitrogen in the third compartment. And in the fourth compartment a cyonabacterium such as Arthrospira sp. will photosynthetically convert carbondioxide to produce oxygen and could be used as food supplement by the crew.

Based on this selected concepts (i.e. carbon and/or nitrogen cycles, microbial organisms and/or higher plants) mathematical models have been studied and built. Unfortunately, to our knowledge these robust models do not take into account the effects of the space environment. In recognition of the well-advanced results of the project on ground, precursor missions are now required to validate this engineering approach in the presence of non-terrestrial conditions, such as space micro-gravity or reduced gravity and space ionizing radiation. From previous flight and ground simulation experiments we have shown that space flight conditions can alter the physiology and the metabolism of these individually selected bacteria.

Here we propose to test in flight a very simplified concept of an ecosystem: two-species model, with one being a oxygenic photosynthetic autotrophic oxygen producer (by photosynthesis using sunlight) and the other a aerobic heterotrophic oxygen consumer. We propose to couple two microbial cultures on their gas phases (O2/CO2 exchanges) and to remain in batch conditions for the liquid phases. We propose to inhibit the micro-organisms before the launch and to reactivate them after landing. The objectives of this mini-ecosystem, which are compatible with a non-pressurized mission, are on one hand to quantify microbial kinetics and on the other hand to demonstrate the validity of several technologies and technical concepts. It will allow to investigate several technical points, such as: thermal control, radiation and cosmic rays protections, inhibition and reactivation of microbial processes, as would be necessary for a Moon lander.

Therefore we propose several space flight experiments to further investigate the physiological and metabolic response and genetic adaptation of MELiSSA bacteria and a 2 species mini ecosystem to space flight conditions. The strains will be grown in designated culture chambers providing the necessary conditions for growth (temperature, light, medium) during short and longer periods in space on board the FOTON or BION vehicles. In-flight recording of radiation, temperature, pressure and optical density will allow monitoring the kinetics of the cultures during flight. If sample return is possible, additional post flight analysis of the substrates and metabolome will allow evaluating the conversion kinetics and 'space' optimization of the mathematical model describing the metabolic kinetics. Post flight analysis of the cells by flowcytometry and electron microscopy will discover changes in physiology and biofilm structures. Also the DNA, RNA and protein content of the cells will be analyzed post flight to study in detail the molecular response and adaptation of the cells to space flight conditions. Any changes could be of importance for the technological development of microbial monitoring and life support systems.

In this presentation we explain the guidelines of the experiment, we shortly review the biological and technical constraints, and we propose a preliminary design of experiment.