biofilms destruct host membrane by mechanical stress

The vast majority of bacteria in the world live on surfaces by forming structures called biofilms. These communities host thousands to millions of bacteria of different types, and are so biologically complex and active that scientists describe them as 'cities.'

Biofilms are in fact the preferred lifestyle of bacteria. They form them by attaching to each other on surfaces as diverse as the ocean floor, internal organs and teeth: dental plaque is a common example of a biofilm. But biofilms also cause chronic infections

Generally speaking, the interaction between biofilm and host is thought to be biochemical. But there is some evidence to suggest that the physical, mechanical interplay between them might be just as important—and overlooked as an influence on the host's physiology. For example, how do biofilms form on soft, tissue-like materials?

When bacteria form biofilms, they attach onto a surface and begin to divide. At the same time, they bury themselves inside a mix of polysaccharides, proteins, nucleic acids, and debris from dead cells. This mix forms a sticky substance that is called the EPS matrix (EPS stands for extracellular polymeric substances).

As single bacteria grow inside the EPS they stretch or compress it, exerting mechanical stress. The growth of the biofilm and the EPS matrix's elastic properties generate internal mechanical stress.

This revealed that biofilms induce deformations by buckling like a carpet or a ruler. How big the deformations are depends on how stiff the "host" material is and on the composition of the EPS.

The researchers also found that V. cholerae biofilms can generate enough mechanical stress to deform and damage soft epithelial cell monolayers, like those that line the surface of our lungs and intestines. 

 

 

from paper

Biofilms form when bacteria attach onto a solid surface and 29 divide while embedding themselves in a matrix of extracellular polymeric substances (EPS) 30 (2). The biofilm matrix is a viscoelastic material generally composed of a mixture of polysaccharides, proteins, nucleic acids and cellular debris (3). EPS maintains cell-cell cohesion throughout the lifecycle of a biofilm, also making the resident cells more resilient to selective pressures.

The growth of single cells embedded within self-secreted EPS drives biofilm formation. During this process, cells locally stretch or compress the elastic matrix, thereby exerting mechanical stress (8, 9)

 

reference

Alice Cont et al. Biofilms deform soft surfaces and disrupt epithelia, eLife (2020). DOI: 10.1101/2020.01.29.923060

 

2. G. O’Toole, H. B. Kaplan, R. Kolter, Biofilm Formation as Microbial Development.  Annu. Rev. Microbiol. 54, 49–79 (2000). 

3. H. C. Flemming, J. Wingender, The biofilm matrix. Nat. Rev. Microbiol. 8, 623–633  (2010).

8. C. Douarche, J. M. Allain, E. Raspaud, Bacillus subtilis Bacteria Generate an Internal Mechanical Force within a Biofilm. Biophys. J. 109, 2195–2202 (2015). 

9. N. Rivera-Yoshida, J. A. Arias Del Angel, M. Benítez, Microbial multicellular development: mechanical forces in action. Curr. Opin. Genet. Dev. 51, 37–45 (2018).