a1 Department of Molecular Biology and Biotechnology, University of Sheffield, S10 2TN, UK e-mail: firstname.lastname@example.org
a2 Department of Botany and Microbiology, King Saud University, Riyadh, Saudi Arabia e-mail: email@example.com
Recent studies confirm that bacteria exist in the stratosphere. It is generally assumed that these bacteria are exiting from Earth, although it is possible that some are incoming from space. Most stratospheric bacterial isolates belong to the spore-forming genus Bacillus, although non-spore formers have also been isolated. Theoretically, the smaller a bacterium is, the more likely it is to be carried from Earth to the stratosphere. Ultrasmall bacteria have been frequently isolated from Earth environments, but not yet from the stratosphere. This is an anomalous situation, since we would expect such small bacteria to be over represented in the stratosphere-microflora. Here, we show that ultrasmall bacteria are present in the environment on Earth (i.e. in seawater and rainwater) and discuss the paradox of why they have not been isolated from the stratosphere.
(Received July 01 2010)
(Accepted August 09 2010)
(Online publication September 14 2010)