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A bacterium transforms into a long thread to infect cells more quickly and grow without limits

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A bacterium can mutate its shape into an endless thread and multiply by 100 times its size: in this way, it manages to infect more cells in less time. It is a virulent variant of bacterial infection that had not been identified until now.

Biologists at San Diego State University in the United States have identified a new way in which a type of bacteria invades multiple cells within a living organism. Other bacteria often transform into threads, which is called filamentation, in response to dangerous environments or damage to their DNA. But the Bordetella atropi bacterium changes its shape into a long thread, growing up to 100 times the usual size of a bacterium, within 30 hours, without dividing.

According to a press release, it does not do it to repair damage. Actually it serves to continuously grow and spread from one cell to another in a living organism, achieving quickly infect more cells and access additional nutrients for their growth. This is a never-before-seen form of bacterial “attack” on cells: the mechanism has been developed in a new study, recently published in the journal Nature Communications.

Growth in threads

Scientists know that pathogens such as bacteria and viruses face a tough challenge trying to grow intracellularly, due to the availability of limited space and resources, while replicating in a single host cell. Although mechanisms for direct invasion of neighboring host cells in cell cultures have been discovered, science has yet to fully understand how bacteria spread directly between host cells in real time and in living organisms.

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Bacteria that use filamentation to repair damage to their DNA use this method to subtly continue to grow, but delay dividing into new bacterial cells until they can repair the damage caused by stress. Instead, the new species Bordetella atropi takes filamentation or growth in threads as a way to spread from one cell to another in a living organism, but with a totally different purpose than the response to stress.

These bacteria invade host cells, sensing a rich environment and triggering filamentation to rapidly infect more cells. In other words, the research results indicate that the bacterium uses a pathway that normally regulates the size of bacterial cells to trigger filamentation within host cells, which facilitates cell-to-cell spread in the invaded organism.

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unlimited expansion

Thanks to this mechanism, they access a greater number of nutrients and can noticeably increase in size, in virtually unlimited growth. The researchers identified this new process by observing how Bordetella atropi spreads through the body of a roundworm, called Oscheius tipulae.

The bacterium infects nematodes following a fecal-oral route: its action reduces the lifespan and fecundity of the host. According to the leader of the research, Professor Robert Luallen, the study has allowed specialists to see things that no one had seen before in terms of bacterial spreadspecifically inside a living organism.

The researchers stressed that although neither the bacteria nor the roundworm studied can infect humans, it is possible that human pathogens may also employ the same mechanism of spread. In this sense, the discovered process could also be used by other bacteria to form biofilms, bacterial communities adhered to surfaces that can increase the risk of nosocomial infections, among other consequences.

Reference

Bacterial filamentation as a mechanism for cell-to-cell spread within an animal host. Tran, TD, Ali, MA, Lee, D. et al. Nature Communications (2022). DOI:https://doi.org/10.1038/s41467-022-28297-6

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