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Living bacteria discovered in middle and upper troposphere, say researchers

Researchers from the Georgia Institute of Technology have discovered significant numbers of living microorganisms, primarily bacteria, in the middle and upper troposphere (that section of the atmosphere about four to six miles above the Earth’s surface) using genomic techniques.

For the time being, researchers aren’t sure whether the microorganisms habitually reside in this section of the atmosphere or whether they were sent into the middle and upper troposphere from the Earth’s surface. They believe that the microorganisms could play an important role in forming ice that may affect weather and climate.

The microorganisms were evidenced in air samples obtained as part of NASA’s Genesis and Rapid Intensification Process (GRIP) program to examine low- and high-altitude air masses linked to tropical storms. According to a news release from the Georgia Institute of Technology, the sampling was conducted from a DC-8 aircraft over both land and ocean. The news release notes that the sampling occurred before, during and after hurricanes Earl and Karl in 2010.

“We did not expect to find so many microorganisms in the troposphere, which is considered a difficult environment for life,” said Kostas Konstantinidis, an assistant professor in the School of Civil and Environmental Engineering at the Georgia Institute of Technology, in a statement. “There seems to be quite a diversity of species, but not all bacteria make it into the upper troposphere.”

Researchers used a filter system aboard the DC-8 aircraft to gather the microorganisms from outside air entering the plane’s sampling probes. They utilized genomic techniques like polymerase chain reaction (PCR) and gene sequencing to examine the filters. This gave the researchers the ability to identify the microorganisms and estimate their numbers without relying on conventional cell-culture techniques.

Researchers found that samples from air masses over the ocean revealed mostly marine bacteria, while samples from air masses over land showed mostly earthly bacteria. They also discovered convincing evidence that the hurricanes had a big effect on the distribution and dynamics of microorganism populations.

The study revealed that living bacterial cells described approximately 20 percent of the total particles found in the size range of 0.25 to 1 microns in diameter. The study also showed that bacteria outnumbered fungi in the samples by at least one order of magnitude. Researchers also identified 17 different bacteria taxa.

“In the absence of dust or other materials that could provide a good nucleus for ice formation, just having a small number of these microorganisms around could facilitate the formation of ice at these altitudes and attract surrounding moisture,” said Athanasios Nenes, a professor in the Georgia Tech School of Earth and Atmospheric Sciences and School of Chemical and Biomolecular Engineering. “If they are the right size for forming ice, they could affect the clouds around them.”

Researchers think that sea spray transports the microorganisms skyward.

“When sea spray is generated, it can carry bacteria because there are a lot of bacteria and organic materials on the surface of the ocean,” Nenes added

Researchers would like to conduct additional research to determine whether certain types of bacteria are better than others at surviving in the middle and upper troposphere. They also want to learn more about the microorganisms and pin down whether or not they are carrying on metabolic functions four to six miles above the Earth’s surface.

“For these organisms, perhaps, the conditions may not be that harsh,” said Konstantinidis. “I wouldn’t be surprised if there is active life and growth in clouds, but this is something we cannot say for sure now.”

The new experimental setup necessary for this type of research is still being tested in a research setting.

“We have demonstrated that our technique works, and that we can get some interesting information,” Nenes posited. “A big fraction of the atmospheric particles that traditionally would have been expected to be dust or sea salt may actually be bacteria. At this point we are just seeing what’s up there, so this is just the beginning of what we hope to do.”

The study’s findings were recently published in the journal Proceedings of the National Academy of Sciences.

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