Viewing a microcosm through a physics lens
Serratia marcescens biofilms grown on soft (left) and stiff (right) polyacrylamide (PAA) hydrogels. These images reveal the conclusion that biofilms grow faster as substrate stiffness increases. Credit: Syracuse University

This was how Alison Patteson, assistant professor in the College of Arts and Sciences physics department and also a faculty member in the BioInspired Institute began the explanation of why her physics lab was studyingbacteria.

In a paper published by PNAS Nexus, a new journal from Oxford Academic, she and graduate student Merrill Asp, along with the collaboration of Professor Roy Welch of the biology department, describe the surprising findings from their recent work with bacterial colonies that has potential to help shape further understanding.

Patteson and her team wanted to investigate what makes a colony of organisms bond together and grow on different surfaces.

Scientists used to grow colonies on gels made from agar, an extract of red algae.

Instead, Patteson's team made transparent gels that could be tailored to a specific stiffness, which would allow them to take time-lapse videos of colonies growing on them.

Viewing a microcosm through a physics lens
The left image depicts how each small part of the hydrogel moved based on the movement of embedded fluorescent beads. To the right, a mathematical model of an elastic solid is used to calculate the stress exerted by the bacteria. Credit: Syracuse University

There are tiny creatures and big surprises.

When a biofilm grows out, it is strong enough to exert force on the substrate.

Patteson and Asp apply physics to biology in the ways that they process the images, measure the boundaries of the biofilms, and calculate how quickly the boundaries expand. Patteson's team can now measure the forces that the biofilms are putting on the gels, unlike with the less controllable agar. The team was able to show how biofilms exert more pressure on a stiff surface than on a softer one. It makes sense that the biofilms are able to exert more force and move faster because we don't know why.

Patteson acknowledges that there is an overlap of interest with the lab that procured the strains ofbacteria.

Looking ahead.

Patteson suggests that the team might hold a key to understanding much more about organisms big and small. Soft matter and physics can enter here. There are a lot of tools for understanding that we have just begun to use.

More information: Merrill E Asp et al, Spreading rates of bacterial colonies depend on substrate stiffness and permeability, PNAS Nexus (2022). DOI: 10.1093/pnasnexus/pgac025 Citation: Viewing a microcosm through a physics lens (2022, April 28) retrieved 28 April 2022 from This document is subject to copyright. Apart from any fair dealing for the purpose of private study or research, no part may be reproduced without the written permission. The content is provided for information purposes only.