Microbes that thrive within the human body are sharing genes around and some of those genes are traveling very far without their microbial hosts.
A process called "horizontal gene transfer" takes place when a living thing transfers its DNA to a recipient that is not its descendant. It more typically occurs on microorganisms to turbocharge their evolution. It also happens at a higher rate within the human body than anywhere else in nature.
"Horizontal gene transfer is a major force of exchange of genetic information on Earth," explained Gustavo Caetano-Anollés, a professor at the Carl R. Woese Institute for Genomic Biology. "These exchanges allow microorganisms to adapt and thrive, but they are likely also important for human health."
To observe the horizontal gene transfer between the microbes inside the human body, an international team of researchers created a molecular data-mining method. The findings appear in the journal Scientific Reports.
Complicated Family Tree Of Microbes
For their research, the team created an extensive family tree featuring the tens of thousands of bacteria that colonize the human body. The new method allowed the researchers to see beyond the recent transfer of genes between microbes.
The researchers used 1,000 reference bacterial genome samples from the human gut, skin, blood, oral cavity, urogenital tract, and airways provided by the National Institutes of Health Human Microbiome Project. They calculated the rate of gene transfer and direction from the samples.
They confirmed that the rate of gene transfer between microbes in the human body is about 30 percent higher than anywhere else on the planet. They also found that only about 40 percent of gene transfer occurs between microbes living in the same sites in the body. The remaining 60 percent take place between microbes that are very far apart from each other.
However, the research revealed that the most common transfer of genes happened between microbes that are most closely related to each other regardless of whether they are in the same sites or not.
"Some of these could be very old gene transfer events that happened before the microbes colonized the human body," explained Arshan Nasir, a distinguished fellow at the Los Alamos National Laboratory in New Mexico. "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."
The Importance Of Understanding How Microbes Work
The researchers explained that understanding the horizontal gene transfer that occurs between microbes is crucial especially now that drug-resistant pathogens, which are caused by the transfer of drug-resistant genes, are threatening public health.
They said that the method can also be used by other scientists to predict which genes were inherited by individual microbes "vertically" through reproduction and trace the evolution of microbes and of humans.
