Friday, 12 February, 2016
Direct comparison of physical properties of Bacillus subtilis NCIB 3610 and B-1 biofilms
S. Kesel, S. Grumbein, I. Guemperlein, M. Tallawi, A.-K. Marel, O. Lieleg and M. Opitz -
Applied and Environmental Microbiology, 10.1128/aem.03957-15 (2016)
Many bacteria form surface-attached communities known as biofilms. Due to the extreme resistance of these bacterial biofilms towards antibiotics or mechanical stresses, biofilms are of growing interest not only in microbiology but also in medicine and industry. Previous studies have determined the extracellular polymeric substances present in the matrix of biofilms formed by Bacillus subtilis NCIB 3610. However, studies on the physical properties of biofilms formed by this strain are just emerging. In particular, quantitative data on the contribution of biofilm matrix biopolymers to these physical properties is lacking. Here, we quantitatively investigate three physical properties of B. subtilis NCIB 3610 biofilms: the surface roughness and stiffness, as well as the bulk viscoelasticity of these biofilms. We show how specific biomolecules comprising the biofilm matrix formed by this strain contribute to those biofilm properties. In particular, we demonstrate that the surface roughness and surface elasticity of one-day-old NCIB 3610 biofilms are strongly affected to the surface layer protein BslA. For a second strain, B. subtilis B-1, that forms biofilms mainly comprising γ-polyglutamate, we find significantly different physical biofilm properties that are also differently affected by the commonly used anti-bacterial agent ethanol. We show that B-1 biofilms are protected from ethanol-induced changes in the biofilm stiffness and that this protective effect can be transferred to NCIB 3610 biofilms by the solely addition of γ-polyglutamate to growing NCIB 3610 biofilms. Together, our results demonstrate the importance of specific biofilm matrix components for the distinct physical properties of B. subtilis biofilms.