- Extracellular polymeric substances (EPS) are a diverse mixture of high-molecular-weight compounds secreted by microorganisms into their surrounding environment. They primarily consist of polysaccharides, proteins, lipids, nucleic acids, and other biopolymers, forming a hydrated matrix that embeds microbial cells.
- This extracellular matrix is the defining structural feature of biofilms, providing both physical stability and a protective barrier for microbial communities. The composition of EPS varies depending on the species of microorganisms involved, environmental conditions, and the stage of biofilm development, but in all cases, it serves as a dynamic and multifunctional component of microbial life.
- One of the most important functions of EPS is the facilitation of biofilm formation and maintenance. By producing a sticky matrix, microorganisms can adhere to solid surfaces, each other, or even liquid–air interfaces. This adhesion not only anchors the community in place but also allows for close cellular interactions, communication, and coordinated behavior through quorum sensing. The EPS network creates a three-dimensional microenvironment where nutrients are retained, metabolic byproducts are diffused, and gradients of oxygen and other chemicals are established, supporting diverse microbial metabolisms within a single biofilm.
- EPS also provides significant protection to microbial cells. The hydrated gel-like matrix shields organisms from environmental stresses such as desiccation, ultraviolet radiation, pH fluctuations, and exposure to toxic substances, including heavy metals and antimicrobial agents. This protective function makes biofilm-associated microorganisms far more resistant to antibiotics and disinfectants than their planktonic (free-floating) counterparts, posing challenges in clinical, industrial, and environmental contexts. For example, EPS-mediated biofilms contribute to chronic infections, biofouling in pipelines, and reduced efficiency in water treatment systems.
- Beyond protection, EPS plays a vital role in structural and functional diversity within biofilms. It acts as a scaffold that gives mechanical strength, while its chemical heterogeneity allows for the sequestration of nutrients, cations, and enzymes. Some EPS components even serve signaling roles, influencing gene expression and microbial differentiation. In natural ecosystems, EPS contributes to sediment stability, biogeochemical cycling, and interactions between microorganisms and higher organisms. For instance, in soils and aquatic environments, EPS enhances the aggregation of particles and promotes the retention of moisture and nutrients, supporting overall ecosystem functioning.
- From an applied perspective, EPS has attracted growing interest in biotechnology and environmental engineering. Its capacity to bind metals and pollutants makes it useful in bioremediation and wastewater treatment. EPS-based materials are also studied for applications in food, pharmaceuticals, and biomaterials, owing to their biocompatibility and biodegradability. At the same time, understanding EPS is critical for developing strategies to prevent or disrupt harmful biofilms in medical and industrial settings. Thus, extracellular polymeric substances represent both a challenge and an opportunity: a complex microbial product that underpins biofilm resilience while offering potential pathways for innovation in sustainable technologies.
