Japan Astrobiology Mars Project (JAMP): Search for Microbes on The Mars Surface with Special Interest in Methane-Oxidizing Bacteria

抄録

Liquid water is considered to be critical for life. Gibbs free energy is another factor that is important to sustain life for long durations. Gibbs free energy is obtained by reactions between reductants and oxidants, or from any other non-equilibrium state of matter. As an example, aerobic organisms use carbohydrates and oxygen to obtain energy. Many types of chemoautotrophic mechanisms are known for this process as well. On the surface of Mars, methane and oxidative compounds such as ferric oxide, sulfate and perchloride, which could provide redox-derived Gibbs free energy, have been detected. Iron-dependent methane oxidizing bacteria have been found in marine environments on Earth. This finding suggests the possible presence of methane-oxidizing bacteria on the Mars surface, if the local thermal environment and other resources permit proliferation and metabolism of bacteria. Our project aims to search for methane-oxidizing microbes on the Mars surface. Martian soil will be sampled from a depth of about 5 - 10 cm below the surface, where organisms are expected to be protected from the harsh hyper-oxidative environment of the Mars surface. Small particles less than 0.1 mm or 1 mm will be sieved from the sample, before being transferred to the analysis section by a micro-actuator. The particles will be stained with a cocktail of fluorescent reagents, and examined by fluorescence microscopy. A combination of fluorescent dyes has been selected to identify life forms in samples. A membrane-specific dye or a combination of dyes will be used to detect membranes surrounding the "cell". An intercalating fluorescent dye such as SYBR Green will be used to detect genetic compounds such as DNA. A substrate dye that emits fluorescence upon cleavage by a catalytic reaction will be used to detect the catalytic activity of the "cell". A combination of staining reagents has been chosen based on the definition of life. A membrane separating a cell from the ambient environment may lead to identification of an "individual". DNA or genetic material is required for "replication" of the life form. Catalytic reactions carried out by enzymes drive "metabolism". This combination of strategies will also be useful for detecting pre-biotic organic material as well as remnants of ancient life. Hydrolysis of the polymers in the "cell" followed by HPLC or soft ionization MS for amino acid analysis will be effective for examining whether Martian life is identical to or different from terrestrial life. The number and type of the amino acids as well as their chirality will be analyzed to distinguish whether the polymers are contaminants from Earth.