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The biofilm matrix
Hans-Curt Flemming and Jost Wingender
Abstract | The microorganisms in biofilms live in a self-produced matrix of hydrated extracellular polymeric substances (EPS) that form their immediate environment. EPS are mainly polysaccharides, proteins, nucleic acids and lipids; they provide the mechanical stability of biofilms, mediate their adhesion to surfaces and form a cohesive, three-dimensional polymer network that interconnects and transiently immobilizes biofilm cells. In addition, the biofilm matrix acts as an external digestive system by keeping extracellular enzymes close to the cells, enabling them to metabolize dissolved, colloidal and solid biopolymers. Here we describe the functions, properties and constituents of the EPS matrix that make biofilms the most successful forms of life on earth.
Biofilm
A loose definition for microbial aggregates that usually accumulate at a solidliquid interface and are encased in a matrix of highly hydrated EPS. Included in this definition are cell aggregates such as flocs (floating biofilms) and sludge, which are not attached to an interface but which share the characteristics of biofilms. Multispecies biofilms can form stable microconsortia, develop physiochemical gradients, and undergo horizontal gene transfer and intense cellcell communication, and these consortia therefore represent highly competitive environments.
Microorganisms do not live as pure cultures of dispersed single cells but instead accumulate at interfaces to form polymicrobial aggregates such as films, mats, flocs, sludge or biofilms (REF. 1). In most biofilms, the microorganisms account for less than 10% of the dry mass, whereas the matrix can account for over 90%. The matrix is the extracellular material, mostly produced by the organisms themselves, in which the biofilm cells are embedded. It consists of a conglomeration of different types of biopolymers known as extracellular poly meric substances (EPS) that forms the scaffold for the three-dimensional architecture of the biofilm and is responsible for adhesion to surfaces and for cohesion in the biofilm. The formation of a biofilm allows a lifestyle that is entirely different from the planktonic state. Although the precise and molecular interactions of the various secreted biofilm matrix polymers have not been defined, and the contributions of these components to matrix integrity are poorly understood at a molecular level (REF. 2), several functions of EPS have been determined (TABLE 1), demonstrating a wide range of advantages for the...