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Clouds and Rain Carry a Menagerie of Photosynthetic Microbes

Microbiologists identify diatoms, algae, and cyanobacteria species from samples above a mountaintop in France.

Jun 24, 2019
Chia-Yi Hou

ABOVE: Puy de Dôme, the peak where the cloud water samples were collected
© ISTOCK.COM MARGOUILLATPHOTOS

Although researchers have known that photosynthetic microbes are present in the atmosphere, research has yet to show that they are actively photosynthesizing while airborne, says Kevin Dillon, a graduate student in Donna Fennell’s lab at Rutgers University. In a talk at the American Society for Microbiology meeting in San Francisco this week, Dillon reported on the diversity of microbial species in cloud and rainwater along with evidence suggestive of active photosynthesis.

“There is a lot of life in the atmosphere,” Dillon tells The Scientist. “One of the main things we are trying to see is, Are these things in the air active? First though, to get to activity, you have to assess diversity.”

The research team based at Rutgers collaborated with Pierre Amato and Anne-Marie DeLort at the Université Clermont Auvergne and the French National Centre for Scientific Research in France collected condensed cloud water at the Puy de Dôme meteorological station in France and rainwater from a location nearby. The team sequenced the DNA and report the presence of cyanobacteria species such as Chroococcidiopsis and algae species including Trebouxia, as well as diatoms and dinoflagellates.

The team found algae were the most abundant microbes and the most dominant photosynthetic species were Cyanobacterium spp. and Chloroidium saccharophilum. The microbial species are mostly associated with terrestrial environments and are “pretty tolerant to stress,” according to Dillon. The researchers also cultured the photosynthetic microbes from the clouds, a first for these species as far as they know.

The authors sequenced the RNA and DNA from the samples and analyzed their relative ratios to estimate how active the microbes are. The RNA/DNA ratio from cyanobacteria suggests that because RNA is relatively high that cyanobacteria may be active in clouds, Dillon tells The Scientist.

This could have implications for the carbon cycle. “I’m not saying it’s actually happening, but it could potentially mean those organisms could be fixing carbon dioxide and doing photosynthesis in clouds,” says Dillon.

The microbial species in clouds may also travel long distances while aloft, and this may affect the ecosystems where they eventually land, Dillon tells The Scientist.

Clarification (June 25): The names of collaborators Pierre Amato and Anne-Marie DeLort have been added.

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