The bacteria in the polymer form cable-like structures and grow into a living gel.

Scientists at the California Institute of Technology and Princeton University have found that bacterial cells growing in a slime-like polymer solution form long cables that twist and twist around each other, building a kind of “living Jello.” I discovered that.

This discovery could be particularly important for research and treatment of diseases such as cystic fibrosis. In cystic fibrosis, the mucus lining the lungs becomes more concentrated, often leading to life-threatening bacterial infections that colonize the mucus. The discovery also has implications for the study of polymer-secreting collections of bacteria known as biofilms (for example, the slippery slime found on river rocks) and for industrial applications that can cause equipment failure and health hazards. It is possible to give

The research is described in a paper published January 17 in the journal Science Advances.

“We found that when many bacteria grow in fluids containing spaghetti-like molecules called polymers, such as mucus in the lungs, they form cable-like structures that intertwine like a living gel,” said Professor of Chemical Engineering. says Sujit Datta. Department of Biotechnology and Biophysics at the California Institute of Technology and corresponding author of the new paper. “And interestingly, there are similarities between the physics of how these structures form and the microscopic physics underlying many inanimate gels like Purell and Jell-O.”

Datta recently moved to Caltech from Princeton University. Sebastián González La Corte, a graduate student at Princeton University, is the paper’s lead author. He and Datta were interested in how mucus concentrations change in the lungs and intestines of cystic fibrosis patients, where more polymers are present than normal. Dr. Gonzalez-La Corte used mucus samples provided by colleagues at MIT to grow E. coli (commonly used in laboratory research) in normal fluids and cystic fibrosis-like samples. They then observed the specimens under a microscope to see how the bacterial cells grew. In each case.

He focused on cells that had lost the ability to swim, as is the case with many bacteria in nature. Under normal circumstances, when such a cell divides into two, the resulting cells separate and spread out from each other. But Gonzalez-La Corte found that in a polymer solution, the copied cells remained attached end-to-end.

“As the cells divide and continue to attach to each other, they begin to form beautiful long structures called cables,” Gonzalez-La Corte says. “At some point, they actually fold into each other and form an intertwined network.”

The researchers found that as long as the cells had the nutrients they needed, the cables continued to stretch and grow, eventually forming chains thousands of cells long.

Subsequent experiments showed that it doesn’t seem to matter which bacterial species is introduced, nor does the type of organic polymer solution. When enough polymer surrounds the bacterial cell, a cable grows. The researchers confirmed the same results with bacteria in synthetic polymers.

Although the initial motivation for this study was to better understand the progression of infection in cystic fibrosis patients, the results have broader relevance. Mucus plays an important role in the human body, not only in the lungs but also in the intestines and cervicovaginal canal. And Dutta says the research is also important from the perspective of biofilms, groups of bacteria that grow their own encapsulating polymer matrices. Biofilms such as dental plaque exist on the human body, but they are also very common in soil and industrial environments, where they can damage equipment and pose health risks.

“The polymer matrix they secrete makes it very difficult to remove the biofilm from the surface or treat it with antibiotics,” Datta says. “Understanding how cells grow within that matrix may be the key to finding ways to better control biofilms.”

Understand the physics behind cables

Through carefully designed experiments, the research team discovered that the external pressure exerted by the polymers surrounding dividing cells is what forces them together and holds them in place. In physics, such attractive forces under the control of external pressure are called depletion interactions. Gonzalez La Corte used the theory of depletion interactions to create a theoretical model of bacterial cable growth. This model can predict when a cable will survive and grow in a polymer environment.

“Now we can actually use well-established theories in polymer physics, developed for completely different purposes, in these biological systems to quantitatively predict when these cables will occur. ,” says Dutta.

Why do bacteria form these cables?

“We discovered this interesting, rare and very unexpected phenomenon,” Dutta says. “We can also explain why it happens in terms of mechanisms and physics. The question is: What are the biological effects?”

Interestingly, there are two possibilities. Bacteria may cluster together to form a network of living gels to make themselves larger and more difficult for immune cells to engulf and destroy. Alternatively, it’s possible that cable formation is actually harmful to bacteria. After all, secretions from the host cause the bacteria to build the cables. “Mucus is not static; in the lungs, for example, it is constantly scraped up and propelled upward by tiny hairs on the surface of the lungs,” Datta says. “Does that mean that with all the germs stuck inside these cables, it’s actually easier to remove them, to get them out of the body?”

For now, no one knows which possibility is correct, but Dutta says that’s what keeps the project interesting. “Now that we have discovered this phenomenon, we can frame these new questions and design further experiments to test our suspicions,” he says.