Biofilms are aggregated bacterial communities structured within an extracellular matrix (ECM). ECM controls biofilm architecture and confers mechanical resistance against shear forces. From a physical perspective, biofilms can be described as colloidal gels, where bacterial cells are analogous to colloidal particles distributed in the polymeric ECM. However, the influence of the ECM in altering the cellular packing fraction (ϕ) and the resulting viscoelastic behavior of biofilm remains unexplored. Using biofilms of Pantoea sp. (WT) and its mutant (ΔUDP), the correlation between biofilm structure and its viscoelastic response is investigated. Experiments show that the reduction of exopolysaccharide production in ΔUDP biofilms corresponds with a seven‐fold increase in ϕ, resulting in a colloidal glass‐like structure. Consequently, the rheological signatures become altered, with the WT behaving like a weak gel, whilst the ΔUDP displayed a glass‐like rheological signature. By co‐culturing the two strains, biofilm ϕ is modulated which allows us to explore the structural changes and capture a change in viscoelastic response from a weak to a strong gel, and to a colloidal glass‐like state. The results reveal the role of exopolysaccharide in mediating a structural transition in biofilms and demonstrate a correlation between biofilm structure and viscoelastic response.
Bibliographical noteFunding Information:
T.P.C. and J.C. acknowledge funding from Engineering and Physical Sciences Research Council (UK) through award number EP/K039083/1 to Newcastle University. S.G.V.C. acknowledges the EPSRC DTP studentship from Newcastle University. J.L.M., A.N.B., and S.T.R. acknowledge funding from the Genomic Science Program, U.S. Department of Energy, Office of Science, Biological and Environmental Research, as part of the Plant‐Microbe Interfaces Scientific Focus Area. E.S. acknowledges funding from the SNSF PRIMA grant 179834. This research used resources of the Center for Nanophase Materials Sciences, which was a US Department of Energy, Office of Science User Facility at Oak Ridge National Laboratory. Oak Ridge National Laboratory is managed by UT‐Battelle, LLC, for the U.S. Department of Energy under contract DE‐AC05‐00OR22725. The authors thank Prof. A. Wipat, Prof. J.G. Burgess and Dr. Lucy E. Eland for encouraging discussions and providing access to their laboratories. Assistance from members of the Bio‐imaging unit at Newcastle University is gratefully acknowledged.
© 2023 The Authors. Advanced Science published by Wiley-VCH GmbH.
- extracellular exopolysaccharides
- packing fraction
- Payne effect