The ribosome is a dynamic nanomachine responsible for coded protein synthesis. Its major subsystems were essentially in place at the time of the last universal common ancestor (LUCA). Ribosome evolutionary history thus potentially provides a window into the pre- LUCA world. This history begins with the origins of the peptidyl transferase center where the actual peptide is synthesized and then continues over an extended timeframe as additional functional centers including the GTPase center are added. The large ribosomal RNAs (rRNAs) have grown over time by an accretion process and a model exists that proposes a relative age of each accreted element. We have compared atomic resolution ribosome structures before and after EF-G bound GTP hydrolysis and thereby identified the location of 23 pivot points in the large rRNAs that facilitate ribosome dynamics. Pivots in small subunit helices h28 and h44 appear to be especially central to the process and according to the accretion model significantly older than the other helices containing pivots. Overall, the results suggest that ribosomal dynamics occurred in two phases. In the first phase, an inherently mobile h28/h44 combination provided the flexibility needed to create a dynamic ribosome that was essentially a Brownian machine. This addition likely made coded peptide synthesis possible by facilitating movement of a primitive mRNA. During the second phase, addition of pivoting elements and the creation of a factor binding site allowed the regulation of the inherent motion created by h28/h44. All of these events likely occurred before LUCA.
Previous space flight experience has demonstrated that microorganisms are just as ubiquitous in space habitats as they
are on Earth. Numerous incidences of biofilm formation within space habitats have been reported; some of which were
identified only after damage to spacecraft structures and irritation to astronaut’s skin occurred. As we increase the
duration of spaceflight missions, it becomes legitimate to question the long-term effects of microgravity on bacteria. To
begin this assessment, Escherichia coli K-12 strain MG1655 was grown for one thousand generations (1000G) under
low shear modeled microgravity. Subsequently, growth kinetics and the presence of biofilm were assessed in the 1000G
strain as compared to a strain (1G) briefly exposed to LSMMG. Overall, the analysis revealed that (i) there was no
obvious difference in growth kinetics between the 1G and 1000G strains, and (ii) although biofilm formation was not
seen in the 1G strain it did in fact occur as exposure time increased. The results suggest that long-term exposure to the
space environment likely favors biofilm formation in many organisms.
Evidence pertaining to the evolutionary history of the ribosome is reviewed and is
discussed in the context of the origin of life as we know it on the Earth. The implications for the
search for life elsewhere are also discussed. If extraterrestrial life is found that has complex
protein synthesis machinery, it will be of interest to determine if it represents a second genesis of
life. It is argued that a comparison with the translation machinery of Earth life will be able to
resolve the issue. If such extraterrestrial life were concluded to have arisen from the same
genesis as Earth life, then examination of the ribosomal RNAs will provide further insight. In
particular, it would in many scenarios be possible to determine how recently an organism found
on another body such as Mars had been transferred to or from the Earth. Thus, forward
contamination could be distinguished from interplanetary transfer.
The modern ribosome is a complex biological machine that is responsible for chiral synthesis of cellular proteins
according to the genetic code as specified by a mRNA. Major portions of the ribosomal machinery were likely in place
before the last universal common ancestor (LUCA) of life. The early evolution of the ribosome has implications for the
origin of the genetic code, the emergence of chirality in peptide synthesis, and the emergence of LUCA. Although codon
assignments may remain a mystery, the history of the ribosome provides a context for dating the first usage of mRNA. In
the case of chirality, the modern ribosome suggests that a small initial chiral preference for L-amino acids in the
environment may have been greatly enhanced by a two step process in which the charging of a primitive tRNA and the
subsequent synthesis of a peptide bond both had the same chiral preference. The resulting ability to make largely chiral
peptides may have provided an advantage over other prebiotic mechanisms for making peptides. Finally, the late
addition of factors such as EF-G may have greatly accelerated the emerging ribosome's ability to synthesize proteins,
thereby allowing entities with this novel capability to emerge as the LUCA.
To prevent forward contamination and maintain the scientific integrity of future life detection missions, it is
important to characterize and attempt to eliminate terrestrial microorganisms associated with exploratory
spacecraft and landing vehicles. Among the organisms isolated from spacecraft-associated habitats, spores of
Bacillus pumilus SAFR-032 exhibited unusually high resistance to decontamination techniques such as UVradiation
and peroxide treatment. Subsequently, Bacillus pumilus SAFR-032 was flown to the International
Space Station (ISS) and exposed to a variety of space conditions using the European Technology Exposure
Platform and Experiment Facility (EuTEF). After 18 months exposure in the EuTEF facility under dark space
conditions, SAFR-032 spores showed 10 to 40% survivability, whereas a survival rate of 85 to 100% was
observed when these spores were kept aboard the ISS under dark simulated-Mars atmospheric conditions. In
contrast, when UV (>110nm) was exerted on SAFR-032 spores for the same time period and conditions using
the EuTEF, a ~7-log reduction in viability was noticed. However, the UV exposure still did not inactivate all the
spores as 19 CFUs were later isolated via cultivation. A parallel experiment was conducted on Earth with
identical samples but under simulated conditions. Spores exposed to ground simulations showed less of a
reduction in viability when compared with the "real space" exposed spores (~3-log reduction in viability for
Mars UV, and ~4-log reduction in viability for Space UV). The data generated is important to assess the
probability and mechanisms of microbial survival, microbial contaminants of risk for forward contamination, in
situ life detection, and to safeguard the integrity of sample return missions.
The Microarray Assay for Solar System Exploration (MASSE) is based on the use of immunological reactions to detect chemical compounds in samples of extraterrestrial material. In order for this technology to be useful for in situ studies on any given planet, molecules present within the material examined must be extracted and recognizable to the antibodies used in the assays. Experiments are currently being conducted on the immunological detection of agents in environmental samples, including soils and JSC Mars - 1 Martian regolith simulant and progress to date is discussed in the context of the development of the MASSE instrument.
The protein synthesis machinery is believed to have largely evolved before the last common ancestor of life on Earth as we know it. Thus, an understanding of ribosomal history will provide insight to the transition period between the last common ancestor and the RNA World. It is argued here that much of this history has been preserved in the primary sequences and three-dimensional structures of the various ribosomal components. In order to understand this history, it is necessary to identify timing insights that can provide clues to the relative age of various aspects of the ribosomal machinery. Such information can be obtained in a variety of ways. Several examples of how such information might be obtained are discussed. Finally, a tentative outline of the order of major events in ribosome history is presented.
The Microarray Assay for Solar System Exploration (MASSE) will use a microarray of antibody tests to search for biomarkers in extraterrestrial environments. In order for this technology to be useful for in situ studies on any given planet, molecules present within the material examined must be extracted and recognizable to the antibodies used in the assays. Experiments are currently being conducted on the immunological detection of agents in environmental samples, including soils and JSC Mars - 1 Martian regolith simulant and progress and results of immunological testing of material containing biomarkers for viable life will be presented and discussed in the context of the development of the MASSE instrument.