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Modelling an Extraterrestrial Epidemic
Abstract
Panspermia is the theory that life has been transported between bodies in the solar system by means of asteroid or cometary impact. Assuming that panspermia is true, and that genetically related microbial life exists outside of our planet, then it is possible that such life could pose an infectious threat to the terrestrial biosphere. We offer several assumptions of the characteristics that such life might possess and extrapolate the likely epidemiological compartment approach to be applied when attempting to model the impact of an Earthly epidemic originating from an extraterrestrial pathogen.
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We report the discovery for the first time of diatom frustules in a
carbonaceous meteorite that fell in the North Central Province of Sri Lanka on
29 December 2012. Contamination is excluded by the circumstance that the
elemental abundances within the structures match closely with those of the
surrounding matrix. There is also evidence of structures morphologically
similar to red rain cells that may have contributed to the episode of red rain
that followed within days of the meteorite fall. The new data on fossil diatoms
provide strong evidence to support the theory of cometary panspermia.
Microbiology at the high altitude atmosphere is important for assessing the chances and limits of microbial transfer from the earth to extraterrestrial bodies. Among the microorganisms isolated from the high-atmospheric samples, spore formers and vegetative Deinococci were highly resistant against harsh environment at high altitude. From limited knowledge available to date, it is suggested that terrestrial microorganisms may have had chances to be ejected and transferred to outer space. Survival of these organisms during their space travel and proliferation on other planets might be also feasible. Directed Panspermia from Earth to extraterrestrial bodies is discussed on the basis of findings reported in literatures.
Five bacterial strains have been isolated from dust samples collected from the upper troposphere and lower stratosphere during several aircraft flights. Most of them displayed much higher resistance to ultraviolet radiation (254 nm) than surface airborne isolates. The role of UV radiation combined with other conditions to determine survivability of bacterial species in the upper atmosphere is discussed. Two strains from the upper atmosphere (ST0316 and TR0125) exhibited extreme UV resistance and tend to form cell clumps or aggregates. Forming cell aggregation might be a strategy to enhance their survivability in the harsh conditions such as high dosage of UV at high altitude.
On 13 August 2004, an atmospheric sample was collected at an altitude of 20,000m along a west to east transect over the continental
United States by NASA’s Stratospheric and Cosmic Dust Program. This sample was then shipped to the US Geological Survey’s
Global Desert Dust program for microbiological analyses. This sample, which was plated on a low nutrient agar to determine
if cultivable microorganisms were present, produced 590 small yellow to off-white colonies after approximately 7weeks of
incubation at room-temperature. Of 50 colonies selected for identification using 16S rRNA sequencing, 41 belonged to the family
Micrococcaceae, seven to the family Microbacteriaceae, one to the genus Staphylococcus, and one to the genus Brevibacterium. All of the isolates identified were non-spore-forming pigmented bacteria, and their presence in this sample illustrate that
it is not unusual to recover viable microbes at extreme altitudes. Additionally, the extended period required to initiate
growth demonstrates the need for lengthy incubation periods when analyzing high-altitude samples for cultivable microorganisms.
An aerobiology sampling flight at 20km was conducted on 28 April 2008 over the Pacific Ocean (36.5° N, 118–149° W), a period
of time that coincided with the movement of Asian dust across the ocean. The aim of this study was to confirm the presence
of viable bacteria and fungi within a transoceanic, atmospheric bridge and to improve the resolution of flight hardware processing
techniques. Isolates of the microbial strains recovered were analyzed with ribosomal ribonucleic acid (rRNA) sequencing to
identify bacterial species Bacillus sp., Bacillus subtilis,
Bacillus endophyticus, and the fungal genus Penicillium. Satellite imagery and ground-based radiosonde observations were used to measure dust movement and characterize the high-altitude
environment at the time of collection. Considering the atmospheric residency time (7–10days), the extreme temperature regime
of the environment (−75°C), and the absence of a mechanism that could sustain particulates at high altitude, it is unlikely
that our samples indicate a permanent, stratospheric ecosystem. However, the presence of viable fungi and bacteria in transoceanic
stratosphere remains relevant to understanding the distribution and extent of microbial life on Earth.
KeywordsUpper atmosphere-Stratosphere-Microbiology-Pacific Ocean
Martian meteorite ALH84001 (ALH) is the oldest known igneous rock from Mars and has been used to constrain its early history.
Lutetium-hafnium (Lu-Hf) isotope data for ALH indicate an igneous age of 4.091 ± 0.030 billion years, nearly coeval with an
interval of heavy bombardment and cessation of the martian core dynamo and magnetic field. The calculated Lu/Hf and Sm/Nd
(samarium/neodymium) ratios of the ALH parental magma source indicate that it must have undergone extensive igneous processing
associated with the crystallization of a deep magma ocean. This same mantle source region also produced the shergottite magmas
(dated 150 to 570 million years ago), possibly indicating uniform igneous processes in Mars for nearly 4 billion years.
Prions are infectious proteins consisting mainly of PrPSc, a β sheet–rich conformer of the normal host protein PrPC, and occur in different strains. Strain identity is thought to be encoded by PrPSc conformation. We found that biologically cloned prion populations gradually became heterogeneous by accumulating “mutants,”
and selective pressures resulted in the emergence of different mutants as major constituents of the evolving population. Thus,
when transferred from brain to cultured cells, “cell-adapted” prions outcompeted their “brain-adapted” counterparts, and the
opposite occurred when prions were returned from cells to brain. Similarly, the inhibitor swainsonine selected for a resistant
substrain, whereas, in its absence, the susceptible substrain outgrew its resistant counterpart. Prions, albeit devoid of
a nucleic acid genome, are thus subject to mutation and selective amplification.
Three novel bacterial strains, PVAS-1(T), B3W22(T) and B8W22(T), were isolated from cryotubes used to collect air samples at altitudes of between 27 and 41 km. Based on phenotypic characteristics, chemotaxonomic features, DNA-DNA hybridization with the nearest phylogenetic neighbours and phylogenetic analysis based on partial 16S rRNA gene sequences (PVAS-1(T), 1196 nt; B3W22(T), 1541 nt; B8W22(T), 1533 nt), the three strains were identified as representing novel species, and the names proposed are Janibacter hoylei sp. nov. (type strain PVAS-1(T) =MTCC 8307(T) =DSM 21601(T) =CCUG 56714(T)), Bacillus isronensis sp. nov. (type strain B3W22(T) =MTCC 7902(T) =JCM 13838(T)) and Bacillus aryabhattai sp. nov. (type strain B8W22(T) =MTCC 7755(T) =JCM 13839(T)).
Evidence of biogenic activity on Mars has profound scientific implications for our understanding of the origin of life on Earth and the presence and diversity of life within the Cosmos. Analysis of the Martian meteorite Allan Hills 84001 (ALH84001) revealed several lines of evidence that has led some investigators to suggest that microbial life existed on Mars approximately 4 billion years ago (45). One of the strongest lines of evidence is the presence of tens-of-nanometer-size magnetite (Fe3O4) crystals found within carbonate globules and their associated rims in the meteorite (57, 58). Approximately one-quarter of these magnetites have remarkable morphological and chemical similarities to magnetite particles produced by magnetotactic bacteria, which occur in aquatic habitats on Earth. Moreover, these types of magnetite particles are not known or expected to be produced by abiotic means either through geological processes or synthetically in the laboratory. We have therefore argued that these Martian magnetite crystals are in fact magnetofossils (57, 58). If this is true, such magnetofossils would constitute evidence of the oldest life forms known. In this respect, we note there is now considerable uncertainty concerning when the earliest terrestrial life forms existed. Until recently, results from the ~3.5-billion-year-old Apex cherts of the Warrawoona group in western Australia held this record (52), although this work is now in question (12).
It is nearly 30 years since the first decisive evidence of microbial morphologies in carbonaceous chondrites was discovered and reported by Hans Dieter Pflug. In addition to morphology, other data, notably laser mass spectroscopy, served to confirm the identification of such structures as putative bacterial fossils. Recent examinations of cometary dust collected in the stratosphere and further studies of carbonaceous meteorites reaffirm the presence of putative microbial fossils. Since carbonaceous chondrites (particularly Type 1 chondrites) are thought to be extinct comets the data reviewed in this article provide strong support for theories of cometary panspermia.
Theories and hypotheses in science are continually subject to verification, critical re-evaluation, revision and indeed evolution, in response to new observations and discoveries. Theories of the origin of life have been more constrained than other scientific theories and hypotheses in this regard, through the force of social and cultural pressures. There has been a tendency to adhere too rigidly to a class of theory that demands a purely terrestrial origin of life. For nearly five decades evidence in favour of a non-terrestrial origin of life and panspermia has accumulated which has not been properly assessed. A point has now been reached that demands the serious attention of biologists to a possibly transformative paradigm shift of the question of the origin of life, with profound implications across many disciplines.
A joint effort between the U.S. Geological Survey's (USGS) Global Desert Dust and NASA's Stratospheric and Cosmic Dust Programs identified culturable microbes from an air sample collected at an altitude of 20,000 m. A total of 4 fungal (Penicillium sp.) and 71 bacteria colony-forming units (70 colonies of Bacillus luciferensis believed to have originated from a single cell collected at altitude and one colony ofBacillus sphaericus) were enumerated, isolated and identified using a morphological key and 16S rDNA sequencing respectively. All of the isolates identified were spore-forming pigmented fungi or bacteria of terrestrial origin and demonstrate that the presence of viable microorganisms in Earth's upper atmosphere may not be uncommon.
The following idea is analysed. Given that evolution on Earth seems to have passed through protocellular evolutionary stages of progenotes, this would appear to be incompatible with the panspermia theory because this observation would imply that the infection bringing life to the Earth started in these protocells, for which a low or null infective power is generally expected.
Lasting commitment to cosmic chemistry and an awareness of the fascinating role of comets in that study was a consequence of an association with Harold Urey early in my astronomical career. Urey's influence on cometary research spread as colleagues with whom I was associated, in turn, developed their own programs in cometary chemistry. One phase of the Chicago research shows that Whipple's icy nucleus would be below about 250 K. This property, combined with their small internal pressure, means cometary interiors remain essentially unchanged during their lifetime. Observations of cometary spectra indicate that they are rich in simple organic species. Experiments on comet-like ice mixture suggests that the extensive array of interstellar molecules also may be found in comets. The capture of cometary debris by the earth or the impact of comets would have been an early source of biochemically significant molecules. Recent hypotheses on radiogenic heating and melting of water ice in the central zone of nuclei do not seem consistent with recent observations or ideas of structure. Thus comets are not a likely place for life to develop.
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