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How do microorganisms reach the stratosphere?

Wainwright, M., Alharbi, S. and Wickramasinghe, N.C. (2006) How do microorganisms reach the stratosphere? International Journal of Astrobiology, 5 (1). pp. 13-15. ISSN 1473-5504


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A number of studies have demonstrated that bacteria and fungi are present in the stratosphere. Since the tropopause is generally regarded as a barrier to the upward movement of particles it is difficult to see how such microorganisms can reach heights above 17 km. Volcanoes provide an obvious means by which this could be achieved, but these occur infrequently and any microorganisms entering the stratosphere from this source will rapidly fall out of the stratosphere. Here, we suggest mechanisms by which microorganisms might reach the stratosphere on a more regular basis; such mechanisms are, however, likely only to explain how micrometre to submicrometre particles could be elevated into the stratosphere. Intriguingly, clumps of bacteria of size in excess of 10 μm have been found in stratospheric samples. It is difficult to understand how such clumps could be ejected from the Earth to this height, suggesting that such bacterial masses may be incoming to Earth.

We suggest that the stratospheric microflora is made up of two components: (a) a mixed population of bacteria and fungi derived from Earth, which can occasionally be cultured; and (b) a population made up of clumps of, viable but non-culturable, bacteria which are too large to have originated from Earth; these, we suggest, have arrived in the stratosphere from space. Finally, we speculate on the possibility that the transfer of bacteria from the Earth to the highly mutagenic stratosphere may have played a role in bacterial evolution.

Item Type: Article
Copyright, Publisher and Additional Information: © 2006 Cambridge University Press. Reproduced in accordance with the publisher's self-archiving policy.
Keywords: aerobiology, evolution, exobiology, panspermia, stratosphere
Institution: The University of Sheffield
Academic Units: The University of Sheffield > Faculty of Science (Sheffield) > School of Biological Sciences (Sheffield) > Department of Molecular Biology and Biotechnology (Sheffield)
Depositing User: Repository Assistant
Date Deposited: 03 Jan 2007
Last Modified: 04 Jun 2014 16:12
Published Version: http://dx.doi.org/10.1017/S1473550406002825
Status: Published
Publisher: Cambridge University Press
Refereed: Yes
Identification Number: 10.1017/S1473550406002825
URI: http://eprints.whiterose.ac.uk/id/eprint/1556

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