April 11 (UPI) -- Microbes in the human body are swapping genes with one another, according to a new study. Some bacteria genes can even travel across tissue barriers without their microbial hosts.
Scientists were able to identify instances of "horizontal gene transfer" using a new molecular data-mining method.
"Horizontal gene transfer is a major force of exchange of genetic information on Earth," Gustavo Caetano-Anollés, a professor of crop sciences and genomic biology at the University of Illinois, said in a news release. "These exchanges allow microorganisms to adapt and thrive, but they are likely also important for human health. There are some bacteria that cannot live outside our bodies and some without which we cannot live."
Because horizontal gene transfer has enabled the proliferation of antibiotic resistance among pathogens, an improved understanding of the phenomenon has public health implications.
For the new study, scientists constructed family trees of the thousands of microbes that colonize the human body. Powerful computers and sophisticated algorithms helped scientists analyze the relationships among the different trees and differentiated between genes that were shared via inheritance and genes that were acquired via horizontal gene transfer.
"Most current methods for determining horizontal gene transfer compare DNA features or statistical similarity between genomes to identify foreign genes," said Arshan Nasir, researcher at COMSATS University in Pakistan. "This works fairly well for relatively recent gene transfers, but often fails to identify transfer events that occurred millions or billions of years ago."
The new analysis method allowed Caetano-Anollés and Nasir to overcome this problem. Their work -- detailed this week in the journal Scientific Reports -- showed microbes in the human body exchange genes very freely.
"The horizontal exchange between microbes in our bodies is about 30 percent higher than what you'll find on the rest of the planet," Caetano-Anollés said. "This implies that our bodies provide a niche that is unique and facilitates innovation at the microbe level."
Scientists determined the majority of gene transfer activity, 60 percent, occurs between microbes living in different parts of the body -- microbes in gut sharing genes with bacteria living in the blood, for example.
"Some of these could be very old gene transfer events that happened before the microbes colonized the human body," Nasir said. "It also could be that some bacteria colonize different human body sites at different time points in an individual's lifespan. The others could be the result of the transfer of bacterial DNA from one site to another, perhaps through the blood. We need further experimental evidence to test this tantalizing possibility."
By teasing out which portions of microbial genomes were inherited and which were transferred, scientists can gain new insights into the evolutionary histories of different bacteria strains, as well as their evolutionary relationships with the human body.