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Keefe, AD, Miller SL, McDonald G, Bada J.  1995.  Investigation of the Prebiotic Synthesis of Amino-Acids and Rna Bases from Co2 Using Fes/H2s as a Reducing Agent. Proceedings of the National Academy of Sciences of the United States of America. 92:11904-11906.   10.1073/pnas.92.25.11904   AbstractWebsite

An autotrophic theory of the origin of metabolism and life has been proposed in which carbon dioxide is reduced by ferrous sulfide and hydrogen sulfide by means of a reversed citric acid cycle, leading to the production of amino acids. Similar processes hale been proposed for purine synthesis. Ferrous sulfide is a strong reducing agent in the presence of hydrogen sulfide and can produce hydrogen as web as reduce alkenes, alkynes, and thiols to saturated hydrocarbons and reduce ketones to thiols. However, the reduction of carbon dioxide has not been demonstrated. We show here that no amino acids, purines, or pyrimidines are produced from carbon dioxide with the ferrous sulfide and hydrogen sulfide system. Furthermore, this system does not produce amino acids from carboxylic acids by reductive amination and carboxylation. Thus, the proposed autotrophic theory, using carbon dioxide, ferrous sulfide, and hydrogen sulfide, lacks the robustness needed to be a geological process and is, therefore, unlikely to have played a role in the origin of metabolism or the origin of life.

Kminek, G, Bada JL, Pogliano K, Ward JF.  2003.  Radiation-dependent limit for the viability of bacterial spores in halite fluid inclusions and on Mars. Radiation Research. 159:722-729.   10.1667/0033-7587(2003)159[0722:rlftvo];2   AbstractWebsite

When claims for the long-term survival of viable organisms are made, either within terrestrial minerals or on Mars, considerations should be made of the limitations imposed by the naturally occurring radiation dose to which they have been exposed. We investigated the effect of ionizing radiation on different bacterial spores by measuring the inactivation constants for B. subtilis and S. marismortui spores in solution as well as for dry spores of B. subtilis and B. thuringiensis. S. marismortui is a halophilic spore that is genetically similar to the recently discovered 2-9-3 bacterium from a halite fluid inclusion, claimed to be 250 million years old (Vreeland et al, Nature 407, 897-900, 2000). B. thuringiensis is a soil bacterium that is genetically similar to the human pathogens B. anthracis and B. cereus (Helgason et al., Appl. Environ. Microbiol 66, 2627-2630, 2000). To relate the inactivation constant to some realistic environments, we calculated the radiation regimen in a halite fluid inclusion and in the Martian subsurface over time. Our conclusion is that the ionizing dose of radiation in those environments limits the survival of viable bacterial spores over long periods. In the absence of an active repair mechanism in the dormant state, the long-term survival of spores is limited to less than 109 million years in halite fluid inclusions, to 100 to 160 million years in the Martian subsurface below 3 m, and to less than 600,000 years in the uppermost meter of Mars. (C) 2003 by Radiation Research Society.

Kminek, G, Bada JL.  2006.  The effect of ionizing radiation on the preservation of amino acids on Mars. Earth and Planetary Science Letters. 245:1-5.   10.1016/j.epsl.2006.03.008   AbstractWebsite

Amino acids are excellent biomarkers in the search for life on Mars because they are essential for biology as we know it and they are robust enough to survive for billions of years in the cold and dry Martian environment. However, amino acids and other organic compounds on Mars are exposed to the ionizing radiation from space and from the decay of radionuclides. This process and its role in the preservation of organic compounds has not been adequately addressed in the past. Based on measured radiolysis constants of amino acids and radiation dose estimates for Mars we show that the detection of an amino acid signature derived from an early Martian biosphere is not limited by its radiolytic decomposition as long as the amino acids are shielded adequately from space radiation. This indicates clearly the need to access the Martian subsurface in the search for molecular traces of an extinct Martian biosphere. (c) 2006 Elsevier B.V. All rights reserved.

Kminek, G, Bada JL, Botta O, Glavin DP, Grunthaner F.  2000.  MOD: an organic detector for the future robotic exploration of Mars. Planetary and Space Science. 48:1087-1091.   10.1016/s0032-0633(00)00082-9   AbstractWebsite

Searching for extinct or extant life on Mars is part of the future NASA surveyor class missions. Looking for key organic compounds that are essential for biochemistry as we know it or indicative of extraterrestrial organic influx is the primary goal of the Mars Organic Detector (MOD). MOD is able to detect amino acids, amines and PAHs with at least 100 times higher sensitivity than the Viking GCMS experiment. MOD is not capable of identifying specific organic molecules but can assess the organic inventory of amines and PAHs on the planet. MOD can also quantify adsorbed and chemisorbed water and evolved carbon dioxide in a stepped heating cycle to determine specific carbon-bearing minerals. All that comes with no sample preparation and no wet chemistry. The organics can be isolated from the carrier matrix by heating the sample and recovering the volatile organics on a cold finger. This sublimation technique can be used for extracting amino acids, amines and PAHs under Mars ambient conditions. The detection of amino acids, amines and PAHs is based on a fluorescence detection scheme. The MOD concept has functioned as a laboratory breadboard since 1998. A number of natural samples including shells, clays, bones, lambda -DNA and E.-coli bacteria have been used and organic molecules have been extracted successfully in each case. The first prototype of MOD is operational as of early fall of 1999. MOD has been selected for the definition phase of the NASA-MSR 2003 mission. (C) 2000 Elsevier Science Ltd. All rights reserved.

Kminek, G, Botta O, Glavin DP, Bada JL.  2002.  Amino acids in the Tagish Lake meteorite. Meteoritics & Planetary Science. 37:697-701. AbstractWebsite

High-performance liquid chromatography (HPLC) based amino acid analysis of a Tagish Lake meteorite sample recovered 3 months after the meteorite fell to Earth have revealed that the amino acid composition of Tagish Lake is strikingly different from that of the CM and Cl carbonaceous chondrites. We found that the Tagish Lake meteorite contains only trace levels of amino acids (total abundance = 880 ppb), which is much lower than the total abundance of amino acids in the Cl Orgueil (4100 ppb) and the CM Murchison (16 900 ppb). Because most of the same amino acids found in the Tagish Lake meteorite are also present in the Tagish Lake ice melt water, we conclude that the amino acids detected in the meteorite are terrestrial contamination. We found that the exposure of a sample of Murchison to cold water lead to a substantial reduction over a period of several weeks in the amount of amino acids that are not strongly bound to the meteorite matrix. However, strongly bound amino acids that are extracted by direct HCl hydrolysis are not affected by the leaching process. Thus even if there had been leaching of amino acids from our Tagish Lake meteorite sample during its 3 month residence in Tagish Lake ice and melt water, a Murchison type abundance of endogenous amino acids in the meteorite would have still been readily detectable. The low amino acid content of Tagish Lake indicates that this meteorite originated from a different type of parent body than the CM and CI chondrites. The parent body was apparently devoid of the reagents such as aldehyldes/ketones, HCN and ammonia needed for the effective abiotic synthesis of amino acids. Based on reflectance spectral measurements, Tagish Lake has been associated with P- or D-type asteroids. If the Tagish Lake meteorite was indeed derived from these types of parent bodies, our understanding of these primitive asteroids needs to be reevaluated with respect to their potential inventory of biologically important organic compounds.

Kua, J, Bada JL.  2011.  Primordial Ocean Chemistry and its Compatibility with the RNA World. Origins of Life and Evolution of Biospheres. 41:553-558.   10.1007/s11084-011-9250-5   AbstractWebsite

We examine the stability of three key components needed to establish an RNA World under a range of potential conditions present on the early earth. The stability of ribose, cytosine, and the phosphodiester bond are estimated at different pH values and temperatures by extrapolating available experimental data. The conditions we have chosen range from highly acidic or alkaline hydrothermal vents, to the milder conditions in a primordial ocean at a range of atmospheric CO2 partial pressures.