Report: Bacteria ‘fish’ for new DNA
Two bacteria are sitting near free-floating DNA. Suddenly, one bacterium shoots out a long appendage, latches onto a DNA fragment and reels in its catch. It happens fast, but it’s clear: this organism had just gone fishing.
Biologists at Indiana University recently captured this maneuver on camera for the first time.
Their findings, published Monday in the journal Nature Microbiology, verify the existence of a harpoon-like mechanism that scientists have been piecing together for decades.
The work also advances understanding of how bacteria take up DNA from their surroundings, which is called natural transformation. That process is key to the spread of antibiotic resistance, which has made bacterial illnesses increasingly difficult to treat with conventional drugs. Each year an estimated two million Americans become infected with antibiotic-resistant bacteria.
Researchers knew that bacteria rely on fibers called pili to capture foreign DNA. But the exact details have remained elusive because pili — more than 10,000 times thinner than human hair — are so hard to observe, said Lori Burrows, a professor of biochemistry and biomedical sciences at McMaster University in Ontario who was not involved in the study.
“It’s cool to actually see this in action,” she said.
We typically think of genes as passed down vertically, from parent to offspring. But there are also processes called horizontal gene transfer, in which DNA moves laterally between organisms that are not parent and child.
Natural transformation is one example, and it’s an important way in which bacteria, which typically reproduce asexually, introduce variation and new traits into their genetic code, said Dr. Ankur Dalia, an assistant professor of biology and an author of the new paper.
The process has mesmerized biologists since 1928, when a British bacteriologist named Frederick Griffith stumbled across it.
To his amazement, he discovered if he injected a heatkilled, virulent strain of Streptococcus pneumoniae, followed by a live, nonvirulent strain, normally innocuous bacteria would somehow become pathogenic. A “transforming principle” had to be at play, he declared.
Sixteen years later, scientists showed that the transforming principle was in fact a molecule called DNA, providing one of the first clues that DNA carried genetic material.
In their study, Dalia and his colleagues used a custom fluorescent dying process created by Courtney Ellison, a graduate student, and Yves Brun, a biology professor, to visualize natural transformation in Vibrio cholera, the bacterium that causes cholera.