Microbial communities often exist as biofilms, which are structured aggregates of cells encased in a self-produced matrix of extracellular polymeric substances (EPS). This matrix acts as a mortar holding the cellular bricks together in a unified and protected structure. The EPS is a complex, dynamic environment that is important for the biofilm’s integrity, function, and survival. Understanding this matrix is the first step in appreciating how these microbial cities are built and sustained.
Composition of the EPS Matrix
The EPS matrix is a blend of macromolecules providing structural and functional support. Its primary components are polysaccharides, which are long chains of sugar molecules that form a gel-like scaffold. These polysaccharides give the biofilm its slimy consistency and physical structure. This hydrated framework is the main construction material of the biofilm.
Within this polysaccharide gel, a variety of proteins are embedded. Many of these are enzymes that perform active roles. Some proteins help to cross-link the polysaccharide chains to reinforce the matrix architecture, while others are involved in processing nutrients trapped within the EPS.
Another component of the matrix is extracellular DNA (eDNA), released from cells that have died within the biofilm. Instead of being waste, eDNA acts as an important binding agent that enhances structural integrity. It functions as a natural adhesive, strengthening the entire biofilm assembly.
Lipids and other biomolecules are also present in smaller quantities. The specific makeup of the EPS can vary depending on the microbial species and environmental conditions. This variability allows biofilms to adapt their matrix composition to best suit their immediate surroundings.
Key Functions of EPS in Biofilms
The EPS matrix provides functions that are important for the survival and proliferation of the biofilm community. A primary role is providing structural support and facilitating adhesion. The matrix produces powerful adhesive properties that anchor the biofilm firmly to surfaces, from a rock in a stream to a medical implant.
The EPS is also a protective shield. The dense, gel-like matrix forms a physical barrier that is difficult to penetrate. This barrier effectively shields the inner microbes from a variety of external threats, including potent antibiotics, chemical disinfectants, and attacks from a host’s immune system.
The matrix also functions as a resource management system. Its porous nature allows it to trap and concentrate nutrients from the environment. The high water content of the EPS also prevents the cells from desiccating, or drying out, ensuring a stable internal environment.
The environment created by the EPS fosters intercellular interactions. By keeping cells in close proximity, the matrix facilitates processes like quorum sensing, a form of microbial communication that coordinates community behavior. It also enables the transfer of genetic material between cells, promoting adaptation and the spread of traits like antibiotic resistance.
Relevance in Health and Industry
The nature of the EPS matrix has significant consequences in medical and industrial settings. In healthcare, biofilms are a major source of persistent and difficult-to-treat infections. They can form on medical devices such as catheters, artificial joints, and heart valves, where the EPS shields the embedded bacteria from antibiotics and the patient’s immune response, making infections chronic and resistant to therapy.
A familiar example of a biofilm is dental plaque. This sticky film on teeth is a classic biofilm where the EPS matrix binds bacteria to the tooth surface. Biofilms are also a complication for individuals with cystic fibrosis, forming difficult-to-eradicate lung infections. They are also a feature of non-healing chronic wounds, where the biofilm prevents effective treatment.
In industrial contexts, biofilms are the cause of biofouling. They grow on equipment, leading to operational and economic problems. Biofilms can clog pipes, contaminate processes, and reduce the efficiency of heat exchangers. On ship hulls, biofilm growth increases drag, which raises fuel consumption.
Not all biofilms are detrimental, and their properties can be harnessed for beneficial purposes. In wastewater treatment plants, biofilms are used to break down and remove pollutants from water. The EPS matrix in these systems immobilizes the beneficial bacteria to efficiently process wastewater.
Targeting the EPS for Biofilm Control
Given the protective role of the EPS, researchers are developing strategies that target this matrix to control unwanted biofilms. One approach involves using enzymes that digest the structural components of the matrix. For example, enzymes called DNases can break down eDNA to weaken the matrix’s integrity.
Other enzymes, known as glycosidases, can degrade the polysaccharide chains that form the primary scaffold of the EPS. By dissolving these structural elements, the biofilm is destabilized and more easily removed or penetrated by antimicrobial agents.
Another strategy focuses on preventing EPS production. This involves using molecules that interfere with microbial signaling pathways, like quorum sensing, that regulate EPS production. Blocking these signals prevents bacteria from building their protective matrix, which inhibits the formation of a mature biofilm.
These anti-EPS strategies represent a shift from traditional antimicrobial approaches. Instead of trying to kill the bacteria directly, these methods aim to disarm them by removing their defense mechanism. By targeting the EPS, it may be possible to develop more effective treatments for chronic biofilm-based infections and new solutions for preventing industrial biofouling.