Do bacteria prefer to travel by air?

An international team of scientists has proposed that the world’s bacteria may by travelling thousands of kilometres through the air instead of hitching rides with people and animals. Their ‘air bridge’ hypothesis could shed light on how harmful bacteria share antibiotic resistance genes.

The proposal arose when a research team led by Konstantin Severinov, currently a professor of molecular biology and biochemistry at Rutgers University–New Brunswick, studied the ‘molecular memories’ of bacteria from their encounters with viruses, stored in special regions of bacterial DNA called CRISPR arrays. Cells that survive infections pass the memories — small pieces of viral DNA — to their offspring, and the order of these memories allows scientists to follow the history of bacterial interaction with viruses over time.

The researchers collected heat-loving Thermus thermophilus bacteria from hot gravel on Mount Vesuvius and hot springs on Mount Etna in Italy; hot springs in the El Tatio region in northern Chile and southern Chile’s Termas del Flaco region; and hot springs in the Uzon caldera in Kamchatka, Russia. Their work was published in the journal Philosophical Transactions of the Royal Society B.

The scientists assumed that bacteria of the same species living in hot springs thousands of miles apart — and therefore isolated from each other — would have very different memories of their encounters with viruses, because the bacteria all should have independent histories of viral infections. They also thought that bacteria should be evolving very rapidly and become different, much like the famous finches Charles Darwin observed on the Galapagos Islands.

“What we found, however, is that there were plenty of shared memories — identical pieces of viral DNA stored in the same order in the DNA of bacteria from distant hot springs,” Severinov said.

“Our research suggests that there must be a planet-wide mechanism that ensures the exchange of bacteria between faraway places.

“Because the bacteria we study live in very hot water — about 160°F — in remote places, it is not feasible to imagine that animals, birds or humans transport them. They must be transported by air and this movement must be very extensive so bacteria in isolated places share common characteristics.”

The scientists now want to test their air bridge hypothesis by sampling air at different altitudes and locations around the world and by identifying the bacteria there, Severinov said. In order to achieve this, they would need access to planes, drones or research balloons.

“Our analysis may inform ecological and epidemiological studies of harmful bacteria that globally share antibiotic resistance genes and may also get dispersed by air instead of human travellers,” he said.

Image caption: Bacteria were collected from this hot spring in the El Tatio region in northern Chile. Image credit: Yaroslav Ispolatov.

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