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Revolutionary Discoveries in Bacterial Growth in Polymer Solutions
Researchers from Caltech and Princeton University have uncovered a significant phenomenon regarding how bacteria behave in polymer-rich environments, such as mucus. Their research shows that bacteria can create intricate, long structures resembling fibers that twist and intertwine, resembling living gelatinous forms.
This insight has critical implications for understanding diseases like cystic fibrosis, where thick mucus accumulates in the lungs, fostering potentially life-threatening bacterial infections. Additionally, it sheds light on biofilms, which consist of bacteria surrounded by a polymer matrix and can cause equipment failures and health complications across various settings.
The findings are detailed in a study published on January 17 in the journal Science Advances.
According to Sujit Datta, a professor at Caltech and the study’s corresponding author, the research revealed that when multiple bacterial cells multiply in polymer-infused fluids, they develop entwined, cable-like structures much like living gels. He noted that there are intriguing parallels between these biological formations and the physical properties of nonliving gels, such as those found in hand sanitizer or desserts like Jell-O.
Datta transitioned to Caltech from Princeton, where graduate student Sebastian Gonzalez La Corte took the lead on this investigation. The duo was interested in the alterations in mucus concentration seen in cystic fibrosis patients, where the presence of polymers is heightened. Utilizing mucus samples provided by colleagues at MIT, Gonzalez La Corte cultivated E. coli bacteria in both standard liquids and cystic fibrosis-like samples, observing the growth patterns of the bacteria through a microscope.
Gonzalez La Corte concentrated on bacteria that can no longer swim, a common characteristic in various environments. Typically, when bacteria divide, they disperse from one another. However, the experiments demonstrated that in a polymeric solution, the new cells remained interconnected, forming cables as they continued to divide.
“As these cells replicate and stay attached, they create elegant, elongated structures we term cables,” explains Gonzalez La Corte. “Eventually, they start bending and intertwining, forming a complex, entangled network.”
The team observed that as long as the bacteria receive the necessary nutrients, these cables persist in growing, forming chains composed of thousands of bacterial cells.
Additional experiments indicated that the specific bacterial species or types of organic polymer did not significantly impact this phenomenon. Once the bacteria are surrounded by ample polymer, the cable formation is consistent. Interestingly, the same results were seen with synthetic polymers as well.
While the study initially aimed to understand bacterial infection growth in cystic fibrosis patients, the findings have broader implications. Mucus plays essential roles in various human systems, including the lungs, intestines, and reproductive tract. Datta underscores the relevance of this work in exploring biofilms, which are bacterial clusters that deposit their own polymer matrix. Such biofilms are prevalent in the human body as dental plaque and are also common in various industrial contexts, where they can lead to equipment damage and pose health risks.
“The tough polymer matrix formed by biofilms makes them particularly challenging to remove from surfaces or treat with antibiotics,” Datta states. “Insights into how bacteria grow within these matrices could be crucial for developing strategies to manage biofilms more effectively.”
Examining the Physics of Bacterial Cable Formation
The research team designed rigorous experiments to reveal that the force exerted by the surrounding polymers is key in holding the bacteria together as they divide. This attractive interaction, driven by external pressure, is identified in physics as a depletion interaction. Gonzalez La Corte employed this theory to construct a model predicting the conditions necessary for bacterial cable growth in polymer-rich environments.
“We can now utilize established theories from polymer physics, originally developed for different applications, to quantitatively forecast when these cables will emerge in biological contexts,” Datta affirmed.
Exploring the Motivations Behind Cable Formation
The discovery has opened a window into intriguing questions regarding the biological implications of cable formation. Datta points out that there are two potential explanations: bacteria might cluster together within these networks to enlarge themselves, making immune destruction more challenging. Conversely, the presence of protective cables may actually render them more vulnerable, as mucus is dynamic, often being moved by cilia in the lungs. “Could it be that when bacteria are aggregated in cables, they are expelled from the body more easily?” he speculated.
Ultimately, the true reasons behind this phenomenon remain unanswered, signaling a continuing journey for the researchers. “Now that we have documented this occurrence, it enables us to pose new questions and devise further experiments to validate our theories,” Datta concluded.
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