A large number of microbes actually live in the Earth’s upper atmosphere, thriving eight to 15 kilometers above the planet’s surface, according to a new study published today in Proceedings of the National Academy of Sciences (1). The authors now believe these tropospheric microorganisms may be playing a significant role in the planet’s hydrological cycle, cloud formation, and climate.
Using the National Aeronautics and Space Administration (NASA) DC-8 aircraft, Nenes and colleagues collected particle samples before, during, and after tropical storm hurricanes Earl and Karl in both cloudy and cloud-free air masses.
The team collected air particles outside the DC-8 aircraft using a special sample tube and filter system. Once deposited on the filters, the particle samples were frozen and brought back to the team’s lab where the group analyzed the samples using microscopy, PCR, and DNA sequencing to determine the number and species of bacteria in the sample.
The group found that bacteria averaged about 20% of the total particles in the 0.25–1-m diameter range. Overall, the researchers identified 17 different bacterial taxa, some of which are known to metabolize organic compounds present in the atmosphere that affect cloud chemistry. In addition, more than 60% of the bacteria studied were alive. “We were definitely not expecting that,” said Nenes.
His team is currently using metagenomics to understand which genes allow these bacteria to survive at such high altitudes. “We’re looking into the metagenome, and trying to see all the genes that are present and detect whether there is a strong presence of anti-stress genes like the ones that are used to fight UV exposure or the ones that help combat the stress of low humidity,” explained Nenes.
For now, Nenes says there are still many more tests to be done to measure the effect of the bacterial particles on the clouds and climate. “We still haven’t quantified their impact on ice nucleation, but we do know for sure that whenever you have particles that are insoluble in water—and bacteria do not dissolve in water spontaneously—they would interact with water when they form ice at those high altitudes. But quantitatively we just need to carry out some experiments in the lab.”
1. DeLeon-Rodriguez, N., T.L. Lathem, L.M. Rodriguez-R, J.M. Barazesh, B.E. Anderson, A.J. Beyersdorf, L.D. Ziemba, M.Bergin, A. Nenes, and K.T. Konstantinidis. Microbiome of the upper troposphere: Species composition and prevalence, effects of tropical storms, and atmospheric implications. PNAS. Published online January 28, 2013.