The Exo-Polysaccharide Component of Extracellular Matrix is Essential for the Viscoelastic Properties of Bacillus subtilis Biofilms.

Santosh Pandit,Abderahmane Derouiche,Karolina Gaska,Ivan Mijakovic,Tiina Nypelö,Mina Fazilati,Roland Kádár

doi:10.3390/ijms21186755

Abstract

Bacteria are known to form biofilms on various surfaces. Biofilms are multicellular aggregates, held together by an extracellular matrix, which is composed of biological polymers. Three principal components of the biofilm matrix are exopolysaccharides (EPS), proteins, and nucleic acids. The biofilm matrix is essential for biofilms to remain organized under mechanical stress. Thanks to their polymeric nature, biofilms exhibit both elastic and viscous mechanical characteristics; therefore, an accurate mechanical description needs to take into account their viscoelastic nature. Their viscoelastic properties, including during their growth dynamics, are crucial for biofilm survival in many environments, particularly during infection processes. How changes in the composition of the biofilm matrix affect viscoelasticity has not been thoroughly investigated. In this study, we used interfacial rheology to study the contribution of the EPS component of the matrix to viscoelasticity of Bacillus subtilis biofilms. Two strategies were used to specifically deplete the EPS component of the biofilm matrix, namely (i) treatment with sub-lethal doses of vitamin C and (ii) seamless inactivation of the eps operon responsible for biosynthesis of the EPS. In both cases, the obtained results suggest that the EPS component of the matrix is essential for maintaining the viscoelastic properties of bacterial biofilms during their growth. If the EPS component of the matrix is depleted, the mechanical stability of biofilms is compromised and the biofilms become more susceptible to eradication by mechanical stress.

Highlights

Bacterial biofilms are communities of microbial cells embedded within a matrix of polymers of their own synthesis [1,2,3]
Our results indicate that a reduction of the EPS component of the matrix leads to a selective alteration of growth dynamics and to a dramatic B. subtilis biofilm elasticity
We present the development of biofilm viscoelastic properties during growth using the interfacial shear storage modulus, G, as it is the dominant contribution to the measurement torque (G G )

Summary

Introduction

Bacterial biofilms are communities of microbial cells embedded within a matrix of polymers of their own synthesis [1,2,3]. It is well demonstrated that eps-defective mutants developed flat colonies and extremely fragile pellicles [11] These mutant strains are still able to grow in cell chains and are still embedded with extracellular protein matrix in the biofilms [11]. A mutant of TasA was shown to produce thin pellicles with less complexity in comparison with the wild type, the effect on biofilm formation was not as dramatic as that of the eps-defective mutants [10] Another protein BslA produced during biofilm maturation developed a hydrophobic layer on top of the biofilm, where it served as a water-repellent barrier for the community [13]. Extracellular DNA is reported to interact with EPS for the modulation of the 3D architecture of B. subtilis biofilm [14]

Methods

Results

Conclusion