Bacteria are constantly evolving resistance to antibiotics, and it is estimated that over 23,000 people have died from resistant infections in the US. The multiple methods that bacteria use to acquire antibiotic resistant genes are not well understood. However, for the first time a ‘harpoon’ mechanism that bacteria use to gain resistance has been caught on camera.

A new technique enables the bacteria to be stained glowing green. A long thin appendage, known as a pili, can be seen extending out from the bacteria. The pili harpoons a piece of DNA and brings it back to the bacterial body. The process by which bacteria harvest foreign DNA and incorporate it into their genome is termed horizontal gene transfer.

Although hypothesized for decades, this is the first time that horizontal gene transfer has been observed on camera; as the pili is 10,000 thinner than a human hair visualising the process has proved challenging. One of the study authors, Courtney Ellison, says the film demonstrates that gene transfer would not be possible without the pili:

“The size of the hole in the outer membrane is almost the exact width of a DNA helix bent in half, which is likely what is coming across. If there weren’t a pilus to guide it, the chance the DNA would hit the pore at just the right angle to pass into the cell is basically zero.”

It was determined that the tip of the pilus binds to the free ring of DNA – effectively like threading a needle. When the proteins at the tip of the pilus were altered to disrupt DNA binding, the bacteria struggled to take up the DNA. Once bound, the DNA is reeled in by the pilus as it disassembles, resembling a scaffold. Researchers were able to disrupt this process to prevent gene transfer.

Horizontal gene transfer is used by bacteria to spread antibiotic resistance genes throughout the population. By understanding how this process happens, the transfer of resistant genes can be prevented.