We previously reported that spaceflight (STS-90) and tail-suspension stimulated muscle protein ubiquitination and accumulated the degradation fragments. However, in space experiments the side-effects of hypergravity on samples are inevitable during the launch of a space shuttle into space or the reentry. To examine whether hypergravity also caused protein-ubiquitination in skeletal muscle cells, we exposed rat myoblastic L6 cells to various hypergravity conditions. Immunoblot analysis showed that the centrifugation at 2, 3, 30 or 100G for 10 min did not increase the amount of ubiquitinated proteins in L6 cells, whereas the centrifugation at 100G for 1 or 2 hrs significantly induced the protein-ubiquitination. In contrast, heat shock protein 70 (HSP70), another stress-responsive protein, in L6 cells was accumulated only by centrifugation at 100G for more than 10 min. Short-term (10 min) hypergravity including 3 or 100 G did not affect the proliferation and morphological changes in L6 cells. Our present results suggest that the ubiquitination of muscle proteins is less sensitive to hypergravity than the induction of HSP70, and that the effect of hypergravity on protein-ubiquitination and proliferation of skeletal muscle cells may be negligible, as far as its duration is short-term.

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Closure of the materials recycle loop for water-foods-oxygen is the primary purpose of space agriculture on Mars and Moon. A microbial ecological system takes a part of agriculture to process our metabolic excreta and inedible biomass and convert them to nutrients and soil substrate for cultivating plants. If we extend the purpose of space agriculture to the creation and control of a healthy and pleasant living environment, we should realize that our human body should not be sterilized but exposed to the appropriate microbial environment. We are proposing a use of hyper-thermophilic aerobic composting microbial ecology in space agriculture. Japan has a broad historical and cultural background on this subject. There had been agriculture that drove a closed loop of materials between consuming cities and farming villages in vicinity. Recent environmental problems regarding garbage collection and processing in towns have motivated home electronics companies to innovate "garbage composting" machines with bacterial technology. Based on those matured technology, together with new insights on microbiology and microbial ecology, we have been developing a conceptual design of space agriculture on Moon and Mars. There are several issues to be answered in order to prove effectiveness of the use of microbial systems in space. 1) Can the recycled nutrients, processed by the hyper-thermal aerobic composting microbial ecology, be formed in the physical and chemical state or configuration, with which plants can uptake those nutrients? A possibility of removing any major components of fertilizer from its recycle loop is another item to be evaluated. 2) What are the merits of forming soil microbial ecology around the root system of plants? This might be the most crucial question. Recent researches exhibit various mutually beneficial relationships among soil microbiota and plants, and symbiotic ecology in composting bacteria. It is essential to understand those features, and define how to conduct preventive maintenance for keeping cultivating soil healthy and productive. 3) Does microbial ecology contribute to building sustainable and expandable human habitation by utilizing the on site extraterrestrial resources? We are assessing technical feasibility of converting regolith to farming soil and structural materials for space agriculture. In the case of Mars habitation, carbon dioxide and a trace amount of nitrogen in atmosphere, and potassium and phosphor in minerals are the sources we consider. Excess oxygen can be accumulated by woods cultivation and their use for lumber. 4) Is the operation of space agriculture robust and safe, if it adopts hyper-thermophilic aerobic microbial ecology? Any ecological system is complex and non-linear, and shows latency and memory effects in its response. It is highly important to understand those features to design and operate space agriculture without falling into the fatal failure. Assessment should be made on the microbial safety and preparation of the preventive measures to eliminate negative elements that would either retard agricultural production or harm the healthy environment. It is worth to mention that such space agriculture would be an effective engineering testbed to solve the global problem on energy and environment. Mars and Moon exploration itself is a good advocate of healthy curiosity expressed by the sustainable civilization of our humankind. We propose to work together towards Mars and Moon with microbial ecology to assure pleasant habitation there.

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