COurtesy of the University of Arizona

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Scientists at the University of Arizona have discovered that some bacteria can use bundles of the minute filaments on their surface to pull on a nearby cell or other surroundings with a force equal to 100,000 times their own weight. And this force lulls a human cell into allowing infection by the bacteria.

The findings could affect both the medical and biophysics fields, those involved said, and may even lead to preventing or limiting certain infectious diseases. The research also may have commercial applications, researchers said.

"This is just the tip of the iceberg," said Dustin Higashi, a senior research specialist with the UA's Bio5 Institute.

Bacteria use their "hair-like appendages" to pull on a cell at the start of an infection, said Magdalene So, a professor of immunobiology and a member of the Bio5 Institute who headed the UA end of the bacteria research. The human cell responds by releasing certain chemicals that call the surrounding bacteria to form into one pile and all pull on the human cell together, she said.

Counterintuitively, this causes the cell to lower its defenses, and the infection proceeds.

Some of the bacteria that use this method of infection include tuberculosis, meningitis and the bacterium used in the research, gonorrhea. The filaments are properly known as Type IV pili, and the bundles formed consist of eight to 10 filaments, although there might be many bundles pulling on a cell.

The study included researchers from Columbia University at Université Paris 7.

Working in conjunction, the researchers measured the force of the pili by placing the bacteria on a network of very small elastic pillars.

When the pili pulled on the pillars, the force then could be calculated. This method was first developed in Paris, So said.

The pili also are used by bacteria to move around and to exchange genetic material with each other.

The incredible strength with which the pili can retract is a result of a nanomotor in the bacterium, the molecular process that turns energy into movement. It is "one of the strongest biomotors that's known," So said.

The study of biological nanomotors is still very new, but there have been suggestions about incorporating them into artificial devices.

"Everyone's talking about biomotors," So said.

"It was originally thought that bacteria attach statically," Higashi said.

The dramatic way in which the bacteria pili affect cells as part of the infection process was part of his work. "Bacteria need it to temporarily progress in infection," he said

"Bacteria can communicate with the human body in very surprising ways," So said.

Knowing the pull of a group of bacteria actually calms down a cell may aid the understanding of communication at the cellular level, and help fight infectious diseases including E. coli, and bacteria known for infecting burns.

"If you understand the process of infection, you can target different aspects," Higashi said. Therapies and vaccines disrupting this method of infection thus could benefit many people, although any such procedures would be somewhere in the future.

"One would think the cell would be destroyed by the pulling," So said. Submitting to the infection "encourages survival and preserves the cell," So said, which may be why it works as it does. An upcoming paper will explain some of the biochemical steps taken by a cell to help it survive infection.

Another aspect of the research of So's lab is to try to understand why some bacteria harm humans when they infect the body whereas others do no harm or even help in some way. For instance, there is a type of E. coli, closely related to the one that causes illness, that lives in human intestines and produces vitamin K.

The motor mechanism behind the pili is still little understood. So next plans on studying that mechanism and how it enables a microbe to retract with such overwhelming force, 10,000 times its' weight from a single filament. So has been working with these bacteria for more than 20 years but said a lot of this research is still "new and unexplored territory."