Spreading rates of bacterial colonies depend on substrate stiffness and permeability

Merrill E Asp; Minh-Tri Ho Thanh; Danielle A Germann; Robert J Carroll; Alana Franceski; Roy D Welch; Arvind Gopinath; Alison E Patteson

doi:10.1093/pnasnexus/pgac025

Spreading rates of bacterial colonies depend on substrate stiffness and permeability

PNAS Nexus. 2022 Apr 15;1(1):pgac025. doi: 10.1093/pnasnexus/pgac025. eCollection 2022 Mar.

Authors

Merrill E Asp^{1

2}, Minh-Tri Ho Thanh^{1

2}, Danielle A Germann^{1

2}, Robert J Carroll^{1

2}, Alana Franceski^{2

3}, Roy D Welch^{2

3}, Arvind Gopinath^{4

5}, Alison E Patteson^{1

2}

Affiliations

¹ Physics Department, Syracuse University, Syracuse, NY 13244, USA.
² BioInspired Institute, Syracuse University, Syracuse, NY 13244, USA.
³ Biology Department, Syracuse University, Syracuse, NY 13244, USA.
⁴ Department of Bioengineering, University of California, Merced, Merced, CA 95343, USA.
⁵ Health Sciences Research Institute, University of California, Merced, Merced, CA 95343, USA.

Abstract

The ability of bacteria to colonize and grow on different surfaces is an essential process for biofilm development. Here, we report the use of synthetic hydrogels with tunable stiffness and porosity to assess physical effects of the substrate on biofilm development. Using time-lapse microscopy to track the growth of expanding Serratia marcescens colonies, we find that biofilm colony growth can increase with increasing substrate stiffness, unlike what is found on traditional agar substrates. Using traction force microscopy-based techniques, we find that biofilms exert transient stresses correlated over length scales much larger than a single bacterium, and that the magnitude of these forces also increases with increasing substrate stiffness. Our results are consistent with a model of biofilm development in which the interplay between osmotic pressure arising from the biofilm and the poroelastic response of the underlying substrate controls biofilm growth and morphology.

Keywords: bacterial colonies; biofilms; hydrogels; mechanobiology; traction force microscopy.