Harpoon for DNA
Scientists have seen for the first time how bacteria gain resistance to antibiotics
Sergey Vasiliev, Naked Science
The spread of new traits among bacteria is possible not only "vertically", from parents to offspring, but also by horizontal transfer – between cells in the population. This happens due to genetic transformation, absorption by the cell of random free DNA chains from the external environment and embedding them into its own genome. Antibiotic resistance can also be transmitted in this way, which makes the study of this mechanism especially relevant.
Scientists from Indiana University for the first time managed to see this process directly, using a microscope and a new method of observation. Ankur Dalia and his co-authors write about this in an article published in the journal Nature Microbiology (Ellison et al., Retraction of DNA-bound type IV competence pili initiates DNA uptake during natural transformation in Vibrio cholerae).
At any moment, only a small part of the bacterial population is capable of "perceiving" someone else's DNA, but these so-called competent cells play a crucial role in survival. Their shells become more permeable, and pili – specialized growths on the surface are used to absorb DNA. Scientists have stimulated this state of competence in cholera vibrions. A specialized set of fluorescent dyes made it possible to visualize both cells, pili, and DNA.
In separate frames, you can see how the cell pulls out the saw and, capturing a fragment of DNA, pulls it inside.
According to the authors, the saws act like miniature harpoons – tens of thousands of times thinner than a human hair, stretching out from a pore in the cell wall, capturing DNA and retracting back. And the pores are so small that the DNA twists to squeeze into the hole. "It's like sewing with thread," explains Courtney Ellison, one of the authors of the work. – The width of the hole in the outer shell is almost equal to the DNA helix folded in half. If they hadn't been drinking, the chances that the DNA, having pushed into the cell, would pass at the right angle, are practically zero."
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