Geometry of life: Physicists determine what co | newswise

From the line: selena langner

Newswise – From plaque stuck on teeth to pond scum, biofilm can be found almost everywhere. These colonies of bacteria grow in implanted medical devices, our skin, contact lenses, and in our intestines and lungs. They can be found in sewers and drainage systems, on the surface of plants, and even in the ocean.

“Some research says that 80% of infections in the human body may be caused by bacteria growing in biofilms.” voice pokharel They say, Georgia Institute of Technology PHD. student and lead author of a groundbreaking new study that uses physics to investigate how these biofilms grow.

paper, “Biophysical basis of bacterial colony growth,” Posted in nature physics this week, and shows that the fitness of a biofilm – its ability to grow, expand, and absorb nutrients from the medium or substrate – is largely influenced by the contact angle that the edge of the biofilm makes with the substrate. The study also found that this geometry has a bigger impact on fitness than anything else, including the rate at which cells reproduce.

“That was a big surprise for us,” says the corresponding author. peter yunkerAn associate professor at Georgia Tech Physics School, “We expected that geometry would play an important role, and we thought that finding out what the geometry actually is would be important for understanding why the boundary expansion rate is, for example, (the rate at which biofilms expand over time) ) is constant. But we did not start the project thinking that geometry would be the single most important factor.

Understanding how biofilms grow – and what factors contribute to their growth rates – can yield important insights on controlling them, with applications to human health, such as slowing the spread of infection or creating cleaner surfaces. Might be possible. “This opportunity to use physics to learn about complex biological systems excited me,” Pokhrel said. Who is Ph.D. are also. student in yunker’s laboratory, adds up. “Especially on a project that has a lot of applications. The combination of importance to human health and exciting research was really interesting to me.

a new method

While biofilms are ubiquitous in nature, they have proven difficult to study. Because these “microbial cities” are made up of tiny individuals, scientists have struggled to successfully image them.

That changed in 2015, when Juncker began wondering whether interferometryImaging techniques commonly used in physics and materials science can be applied to biofilms. Yunker recalls, “Given my background in physics, I was familiar with its use in materials applications.” “I thought it might be interesting to apply this technique more widely, because we know from decades of physics that surface interfaces contain a lot of information about the processes that form them.”

This technique proved to be simple, effective, and time-efficient, providing nanometer-scale resolution of bacterial colonies. “This allows us to essentially get a picture of the topography – the shape of the surface of the bacterial population – with super-resolution,” says Yunker.

Taking advantage of interferometry, the team began conducting new biofilm experiments, examining how the shapes of colonies changed over time. co-first author gabby steinbachFormerly a postdoctoral scholar in Yunker’s laboratory and now a scientific research coordinator at the University of Maryland, he observed that when each colony was small it had a distinctive shape: a spherical cap, a slice off the top of a sphere, or the shape of a drop. Kind. Of water. It’s a shape that appears frequently in physics, and it piqued the team’s interest.

“A spherical cap is very interesting in physics, because it’s a surface-minimizing shape,” says Pokhrel. “I was curious why a biological material was growing to this size, and we started wondering if there was some physics to it – perhaps geometry involved. And that made us think maybe we could develop a model. And that got me really excited.”

a mathematical mystery

However, the researchers soon encountered a hurdle. “While we could see that the colonies were spherical at first, as they grew, they deviated from that shape,” says Pokhrel. “And the shape they evolved into was difficult to describe with existing spherical cap geometry.”

“The central portion did not grow as fast as it should have to maintain the spherical cap shape,” says Yunker, “and we wanted to connect all of this to range expansion (the rate at which the colony spreads over the surface) ” “But we knew that somehow, geometry was playing a very important role.”

At the end, thomas dayA former graduate student in Yunker’s laboratory, now a postdoctoral fellow at the University of Southern California, and one of the authors of the paper, suggested a strange problem of geometry called Napkin ring problem.

“As soon as we started thinking about the napkin ring problem, we were able to start developing a mathematical toolkit,” says Yunker, “although the solution was not easy.” “We couldn’t find anyone who had ever seen a circular hat napkin ring before, because its application is so rare.”

Pokharel, along with two co-authors, was responsible for the work on the geometry. They found that cells grew faster at the edge of the shape, spreading further towards the medium, while cells in the middle grew upwards, creating a shape unlike that of an egg in a frying pan – if the egg white were spread out. While the yolk was only getting longer.

This was an important discovery: because the cells in the middle were only contributing to the height of the biofilm, the team only had to tell how many cells there were at the edge of the biofilm, and what size they needed to be in order to grow and spread.

After incorporating their findings into a mathematical model, the team found that the contact angle was the most important factor: the angle that the very edge of the biofilm made when it touched the surface on which it was growing. That single geometric quality is even more important for the growth of the biofilm than the rate at which it can regenerate cells.

physics-biology relationship

Overall, the project took more than three years from conception to publication. ,Awaaz has really made an incredible effort in bringing this work to fruition,” says Yunker. “It was many years and many, many experiments. But, the finished product is 100% worth it.

The team hopes the research will pave the way for future studies that could lead to applications such as controlling biofilm growth to help prevent infections.

“Moving forward, there are still a lot of avenues of research,” says Pokharel. For example, looking at competition experiments between biofilms – do longer colonies change their contact angle so they can spread faster? “What role does this geometry play in competition?”

“Biology is complex,” Yunker says. In nature, the surface on which a biofilm is growing may not be as consistent as a laboratory surface, and colonies may contain different mutations or contain more than one species. “But we first need to understand what happens when temperature and nutrient availability are stable.” And while the model is based on how biofilms behave in controlled laboratory environments, it is an important first step in understanding how they might behave in nature.

Citation: Pokhrel, A.R., Steinbach, G., Krueger, A. et al. Biophysical basis of bacterial colony growth. net. Physical. (2024). https://doi.org/10.1038/s41567-024-02572-3

Funding Information: This research was funded by the NIH National Institute of General Medical Sciences and NSF Biomaterials