Monday, March 19, 2018
Most Viruses and Bacteria Fall from the Sky, says Study
3/8/2018 12:41:30 PM
Arthur J. Villasanta - Fourth Estate Contributor

Grenada, Spain (4E) - Almost one billion viruses and more than 20 million bacteria (including those that cause diseases) circulate in the Earth's atmosphere and are deposited in high-mountain places every day, according to an international research project led by the University of Granada that revealed this fact for the first time.

The research findings help to explain why genetically identical viruses have been found in such distant locations and diverse environments. The University of British Columbia (Canada) and San Diego State University (United States) participated in the project. The study was published recently in the ISME Journal: Multidisciplinary Journal of Microbial Ecology.

The mechanisms responsible for the dispersal of these microorganisms at the global scale are remain mostly unknown. This pioneering project, however, marks the first time researchers have quantified the amount of viruses and bacteria deposited in the high mountains of Sierra Nevada in Spain after travelling thousands of kilometers in the Earth's atmosphere. The research team was also able to determine that these viruses and bacteria are primarily transported from the Atlantic Ocean and the Sahara Desert.

Every day almost one billion viruses and more than 20 million bacteria are deposited on each square metre above the atmospheric boundary layer (above 2,500-3,000 meters) in the Sierra Nevada mountain range. The deposition rates of viruses were found to be between 9 and 461 times higher than those of bacteria.

Viruses and bacteria are normally deposited by means of atmospheric rain washout and gravity sedimentation. Rain seems to be less efficient in the removal of viruses from the atmosphere than in the removal of bacteria. This seems to be related to the size of the particles to which viruses and bacteria respectively tend to adhere.

"We have discovered that most of the viruses are of marine origin and are usually transported attached to organic particles, which are smaller than the particles to which bacteria adhere," said Dr Isabel Reche, a Lecturer at the Department of Ecology and main author of the paper.

Bacteria, meanwhile, tend to stick to mineral particles, especially those from the Sahara Desert. This means bacteria and viruses are generally deposited through rain events and dust intrusions.

"The small size of the particles to which viruses preferentially adhere and the low deposition efficiency associated with rain washout means that viruses are able to stay in the atmosphere for longer periods and, consequently, they can be transported over greater distances," said Dr. Reche.

This research helps explain why, for over 20 years, viruses that are genetically identical have been found in very distant parts of the planet and in highly disparate environments. The reason is that viruses travel through the Earth's atmosphere.

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