The whip-like flagella that stream off the ends of some bacteria are typically given credit for motoring microbes forward as they explore their surroundings. But bacterial flagella have another, seemingly contradictory job, a team of researchers has discovered: The tails can help the microbes stick to surfaces when they need to stay put, by wedging into crevasses that the rest of the bacteria can’t fit into. The findings, which appear in a new PNAS Early Edition paper, could help engineers design materials that better resist the accumulation of bacteria on their surfaces.
In fact, the team of MIT and Harvard-based researchers who published the paper was studying such “antifouling” surfaces when they made the discovery. In the human body, bacteria that can attach to surfaces often form massive aggregates called biofilms. Such collections can build up on natural surfaces within the body, or on urinary catheters or other implanted devices, and lead to hard-to-treat infections. Understanding how to break up these biofilms—or how to create materials that resist them in the case of implantable devices—can help treat or prevent these infections.
“We were interested in developing antifouling surfaces that bacteria can’t adhere to,” says first author Ronn Friedlander. “And we noticed that some bacteria actually adhered better to certain bumpy surfaces.”
The observation was a surprise, he says; they expected cracks and bumps to make it harder for bacteria to attach to a surface. To figure out how the bacteria were sticking to the rough material so well, Friedlander et. al. used a scanning electron microscope to zoom in on the microbes—in this case, E. coli cells. They could see filaments extending into the cracks in the surface, even though the bodies of the bacteria couldn’t fit into the spaces. When they repeated the experiments with bacteria lacking flagella, the bacteria no longer attached as well, and no parts of the cells extended into the divots in the surface. Additional experiments confirmed that for bacteria with flagella (which includes E. coli, but not every pathogenic bacteria), the flagellar tails were sticking into cracks.
“When a cell is already adhered to a surface, the flagella tend to keep moving,” says Friedlander. “If the cell is up on a bump and there are some valleys nearby, it will move around and reach into those valleys.”
Once it finds a spot to attach, flagella likely use the same adhering proteins to stick to the surface that the rest of the cell uses—the researchers are planning more studies to understand the adherence mechanism.
Friedlander and his colleagues hope that their discovery could lead to the development of surfaces that prevent flagellar attachment, either through specially designed contours that don’t allow flagella to wedge into cracks, or chemical treatments that prevent adherence. Either way, it’s a new direction forward for those studying biofilms.
“It’s interesting to see how bacteria interact with surfaces that aren’t flat, because in the body you have lots of surfaces that aren’t flat,” says Friedlander. “And the other side of it is that, knowing that, it gives us a little more insight into how we can design new antifouling surfaces.”