Study shows that rain transports marine viruses

Microbes move back and forth between the marine and atmospheric ecosystems, i.e.ocean, air and precipitation. However, until now there has been no evidence of the cycle of microbiological spread. Biologist Janina Rahlff from the Linnaeus University has succeeded in precisely this together with other researchers from Germany and Italy.

The researchers have collected seawater, sea surface film and foam, as well as rain and near-ground aerosols during four weeks at Tjärnö Marine Station (University of Gothenburg) in Bohuslän. Using metagenomics they found the same virus in all ecosystems.

“We were also able to trace an exemplary viral genome based on its mutation patterns and thus follow its path along the natural water cycle," explains Rahlff.

She describes the cycle as follows: "The so-called Neuston organisms and viruses are found in the top centimeter of the sea, including the approximately one-millimeter-thick sea surface film. They are particularly easily transmitted aerosols. Aerosols, in turn, act as nuclei for the condensation of water vapor and are essential for the formation of clouds in the atmosphere. Precipitation such as rain or snow then falls from the clouds."

The researchers concluded that marine viruses and microbial hosts were more likely to occur in the rain if the air masses had previously spent more time over the ocean. What was also striking was the high proportion of the bases guanine (G) and cytosine (C) in the DNA of many viruses in the air and especially from rain.

" These rain-derived viruses were not found in the ocean. "But the immune systems of the microbial hosts from the sea surface had already dealt with them," says Rahlff. "So the viruses from the rain had left a kind of footprint in the ocean."

These scientific findings can help better understand the emergence and spread of new viruses. 

"I am particularly interested in where the virus population with high GC bases comes from and under what conditions they occur. As heavy rainfall will increase with climate change here in northern Europe, it is important for me to know what is actually raining down upon us.”

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