exopolysaccharide

Exopolysaccharide, or EPS, is a high-molecular-weight polymer of sugars secreted by microorganisms into the extracellular space. EPS are a major component of the extracellular polymeric substance found in biofilms and can be produced by bacteria, cyanobacteria, fungi, and some algae.

EPS vary in composition and structure. They may be homopolysaccharides consisting of a single sugar or heteropolysaccharides composed of multiple monosaccharides. Common units include glucose, galactose, mannose, rhamnose, and uronic acids. Side groups such as acetyl or pyruvate may modify properties like charge and viscosity.

Biosynthesis and export. EPS are synthesized inside cells and secreted to the outside via dedicated membrane proteins and transport systems. In many microorganisms, they accumulate as slime layers or form a matrix that, together with proteins and extracellular DNA, anchors cells in biofilms.

Functions and ecological roles. EPS contribute to desiccation resistance, osmotic protection, and defense against antimicrobial compounds. They promote adherence to surfaces, support biofilm architecture, and can bind metals and organic molecules, influencing nutrient availability and biogeochemical cycles.

Examples and applications. Industrially important EPS include xanthan gum, gellan gum, dextran, alginate, and pullulan, used as thickeners, stabilizers, gelling agents, and emulsion stabilizers. Medical applications include wound dressings and drug delivery systems. EPS also play roles in bioremediation and soil aggregation.

Research perspectives. The diversity of EPS structure and regulatory networks controlling production are active areas of microbiology and biotechnology, with ongoing work to link EPS properties to biofilm behavior and to exploit EPS in materials science.