Abstract
One of the key conditions of the lithopanspermia hypothesis is that microorganisms situated within meteorites could survive hypervelocity entry from space through the Earth’s atmosphere. So far, all experimental proof of this possibility has been based on tests with sounding rockets which do not reach the transit velocities of natural meteorites. We explored the survival of the spore-forming thermophilic anaerobic bacterium, Thermoanaerobacter siderophilus, placed within 1.4-cm thick basalt discs fixed on the exterior of a space capsule (the METEORITE experiment on the FOTON-M4 satellite). After 45 days of orbital flight, the landing module of the space vehicle returned to Earth. The temperature during the atmospheric transit was high enough to melt the surface of basalt. T. siderophilus survived the entry; viable cells were recovered from 4 of 24 wells loaded with this microorganism. The identity of the strain was confirmed by 16S rRNA gene sequence and physiological tests. This is the first report on the survival of a lifeform within an artificial meteorite after entry from space orbit through Earth’s atmosphere at a velocity that closely approached the velocities of natural meteorites. The characteristics of the artificial meteorite and the living object applied in this study can serve as positive controls in further experiments on testing of different organisms and conditions of interplanetary transport.
Highlights
IntroductionThe transport of microorganisms in space is an important issue from theoretical (origin of life on Earth) and practical (planetary protection) perspectives
The transport of microorganisms in space is an important issue from theoretical and practical perspectives
The results of our study demonstrate that the spore-forming thermophilic anaerobic bacterium Thermoanaerobacter siderophilus survived entry into the Earth’s atmosphere within an artificial meteorite
Summary
The transport of microorganisms in space is an important issue from theoretical (origin of life on Earth) and practical (planetary protection) perspectives. One of the most feasible mechanisms of interplanetary transport is the natural transfer of organisms in rocks (lithopanspermia). This should include three main stages: ejection of the rock from a planetary surface, transit in space, and atmospheric entry [1,2,3,4,5]. The majority of species of thermophilic bacteria and archaea are anaerobic organisms and do not need oxygen for growth. Having arrived on the Earth, thermophilic anaerobes could immediately and quickly proliferate and successfully colonize the high-temperature anoxic environment prevailing at that time
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