The fact that bacteria can share genes with each other is fascinating and a little alarming – after all, that's how they're developing resistance to antibiotics so quickly. It's easy to assume that the bugs need to be in close proximity to teach each other, but unfortunately that might not be the case. A new genetic study of bacteria from around the world has found that isolated populations share incredibly similar "molecular memories," suggesting they're basically flying around the world to spread their genes.
When bacteria are infected by viruses known as bacteriophages, they snip small segments of DNA from their attackers and store them, in order to remember how best to resist them in future. These snippets can be passed down to later generations, allowing the microbes to rapidly evolve to cope with new environments and threats.
These molecular memories make a pretty convenient record of all the viruses that a given colony of bacteria have ever encountered. For the new study, scientists from Russia, France, Chile and Israel set out to investigate and compare the genetic histories of isolated bacteria populations.
The team gathered multiple samples of a bacteria species called Thermus thermophilus, which as its name suggests thrives in hot environments. These were sourced from places thousands of miles apart: Mount Vesuvius and Mount Etna in Italy, two hot springs in northern and southern Chile, and hot springs in Kamchatka, Russia.
The researchers then analyzed the stored DNA sequences of these different populations. They expected the colonies to have wildly different genetic histories from each other – logic says that different viruses would show up in these environments, starting the bacteria down different evolutionary paths over time. But to their surprise, there was a strange amount of agreement between them all.
"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," says Konstantin Severinov, senior author of the study. "Our analysis may inform ecological and epidemiological studies of harmful bacteria that globally share antibiotic resistance genes."
The next question is obvious: exactly how are isolated groups of bacteria able to share these genes over such long distances? The researchers hypothesize that the bugs are taking to the skies.
"Our research suggests that there must be a planet-wide mechanism that ensures the exchange of bacteria between faraway places," says Severinov. "Because the bacteria we study live in very hot water – about 160° F (71° C) – 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."
It's not as far-fetched as it sounds. Bacteria and viruses are thought to hitchhike on airborne particles that are swept up into the sky, before raining back down to the surface potentially thousands of miles away from home. Last year a study quantified that amount, and found that every day, hundreds of millions of microbes rain down per square meter.
The researchers plan on investigating the idea further by taking samples of air at different altitudes and locations, and seeing what species of bacteria they find.
The research was published in the journal Philosophical Transactions of the Royal Society B.
Source: Rutgers University
