Organic solids produced from simple C/H/O/N ices by charged particles: applications to the outer solar system

Growth on Carbohydrates from Carbonaceous Meteorites Alters the Immunogenicity of Environment-Derived Bacterial Pathogens

The last decade has witnessed a renewed interest in space exploration. Public and private institutions are investing considerable effort toward the direct exploration of the Moon and Mars, as well as more distant bodies in the solar system. Both automated and human-crewed spacecraft are being considered in these efforts. As inevitable fellow travelers on the bodies of astronauts, spaceships, or equipment, terrestrial microorganisms will undoubtedly come into contact with extraterrestrial environments, despite stringent decontamination. These microorganisms could eventually adapt and grow in their new habitats, where they might potentially recolonize and lead to the infection of the human space travelers. In this article, we demonstrate that clinically relevant bacterial species found in the environment are able to grow in minimal media with sugar compounds identified in extraterrestrial carbon sources. As a surrogate model, we used carbohydrates previously isolated from carbonaceous meteorites. The bacteria underwent an adaptation process that caused structural modifications in the cell envelope that sparked changes in pathogenic potential, both in vitro and in vivo. Understanding the adaptation of microorganisms exposed to extraterrestrial environments, with subsequent changes in their immunogenicity and virulence, requires a comprehensive analysis of such scenarios to ensure the safety of major space expeditions in the decades to come.

Immune recognition of putative alien microbial structures: Host-pathogen interactions in the age of space travel

Human space travel is on the verge of visiting Mars and, in the future, even more distant places in the solar system. These journeys will be also made by terrestrial microorganisms (hitchhiking on the bodies of astronauts or on scientific instruments) that, upon arrival, will come into contact with new planetary environments, despite the best measures to prevent contamination. These microorganisms could potentially adapt and grow in the new environments and subsequently recolonize and infect astronauts. An even more challenging situation would be if truly alien microorganisms will be present on these solar system bodies: What will be their pathogenic potential, and how would our immune host defenses react? It will be crucial to anticipate these situations and investigate how the immune system of humans might cope with modified terrestrial or alien microbes. We propose several scenarios that may be encountered and how to respond to these challenges.

The Hypothesis that the Genetic Code Originated in Coupled Synthesis of Proteins and the Evolutionary Predecessors of Nucleic Acids in Primitive Cells

Although analysis of the genetic code has allowed explanations for its evolution to be proposed, little evidence exists in biochemistry and molecular biology to offer an explanation for the origin of the genetic code. In particular, two features of biology make the origin of the genetic code difficult to understand. First, nucleic acids are highly complicated polymers requiring numerous enzymes for biosynthesis. Secondly, proteins have a simple backbone with a set of 20 different amino acid side chains synthesized by a highly complicated ribosomal process in which mRNA sequences are read in triplets. Apparently, both nucleic acid and protein syntheses have extensive evolutionary histories. Supporting these processes is a complex metabolism and at the hub of metabolism are the carboxylic acid cycles. This paper advances the hypothesis that the earliest predecessor of the nucleic acids was a β-linked polyester made from malic acid, a highly conserved metabolite in the carboxylic acid cycles. In the β-linked polyester, the side chains are carboxylic acid groups capable of forming interstrand double hydrogen bonds. Evolution of the nucleic acids involved changes to the backbone and side chain of poly(β-d-malic acid). Conversion of the side chain carboxylic acid into a carboxamide or a longer side chain bearing a carboxamide group, allowed information polymers to form amide pairs between polyester chains. Aminoacylation of the hydroxyl groups of malic acid and its derivatives with simple amino acids such as glycine and alanine allowed coupling of polyester synthesis and protein synthesis. Use of polypeptides containing glycine and l-alanine for activation of two different monomers with either glycine or l-alanine allowed simple coded autocatalytic synthesis of polyesters and polypeptides and established the first genetic code. A primitive cell capable of supporting electron transport, thioester synthesis, reduction reactions, and synthesis of polyesters and polypeptides is proposed. The cell consists of an iron-sulfide particle enclosed by tholin, a heterogeneous organic material that is produced by Miller-Urey type experiments that simulate conditions on the early Earth. As the synthesis of nucleic acids evolved from β-linked polyesters, the singlet coding system for replication evolved into a four nucleotide/four amino acid process (AMP = aspartic acid, GMP = glycine, UMP = valine, CMP = alanine) and then into the triplet ribosomal process that permitted multiple copies of protein to be synthesized independent of replication. This hypothesis reconciles the “genetics first” and “metabolism first” approaches to the origin of life and explains why there are four bases in the genetic alphabet.

Energy, chemical disequilibrium, and geological constraints on Europa

Europa is a prime target for astrobiology. The presence of a global subsurface liquid water ocean and a composition likely to contain a suite of biogenic elements make it a compelling world in the search for a second origin of life. Critical to these factors, however, may be the availability of energy for biological processes on Europa. We have examined the production and availability of oxidants and carbon-containing reductants on Europa to better understand the habitability of the subsurface ocean. Data from the Galileo Near-Infrared Mapping Spectrometer were used to constrain the surface abundance of CO(2) to 0.036% by number relative to water. Laboratory results indicate that radiolytically processed CO(2)-rich ices yield CO and H(2)CO(3); the reductants H(2)CO, CH(3)OH, and CH(4) are at most minor species. We analyzed chemical sources and sinks and concluded that the radiolytically processed surface of Europa could serve to maintain an oxidized ocean even if the surface oxidants (O(2), H(2)O(2), CO(2), SO(2), and SO(4) (2)) are delivered only once every approximately 0.5 Gyr. If delivery periods are comparable to the observed surface age (30-70 Myr), then Europa's ocean could reach O(2) concentrations comparable to those found in terrestrial surface waters, even if approximately 10(9) moles yr(1) of hydrothermally delivered reductants consume most of the oxidant flux. Such an ocean would be energetically hospitable for terrestrial marine macrofauna. The availability of reductants could be the limiting factor for biologically useful chemical energy on Europa.

Radiolysis of aqueous formaldehyde relevant to cometary environments

The radiation chemistry of aqueous solutions of formaldehyde was studied in order to obtain an insight into the possible role of ionizing radiation on cometary environments. Aqueous solutions of 1.0 mol dm-3 formaldehyde were exposed to gamma-radiation in the dose range from 0.01 to 1200 kGy at 298 K. The radiation chemical yield of decomposition of formaldehyde was determined to be: G(-CH2(OH)2)-26.3 +/- 1.2. The high radiation chemical yield of decomposition was explained by a chain reaction initiated by the radical CH(OH)2 with formaldehyde. Computer fitting of the experimental data gives k(CH(OH)2 + CH2(OH)2)- 8.0xl0(1) dm3 mol-1 s-1. In the computer treatment of experimental findings we used 54 equations to consider the radiolysis of water and 11 reactions for the radiolysis of aqueous formaldehyde. Based on previous estimates of the total dose of ionizing radiation that comets have accumulated over 4.6 billion years, we predict a radiation damage-depth curve of formaldehyde in comet nuclei.