Exopolymers

Exopolymers are high-molecular-weight macromolecules secreted by microorganisms into the external environment. The most common class is exopolysaccharides (EPS), although proteins, nucleic acids and other polymers may also be released. In biofilms, exopolymers form a hydrated matrix that embeds cells and helps organize the community.

Biosynthesis and secretion: Many bacteria, fungi, and microalgae produce exopolymers. Production is influenced by nutrients, stress, and quorum-sensing signals; export mechanisms vary and can involve dedicated secretion systems and transporters. EPS often contain uronic acids, acetyl groups, and charged groups, giving them diverse chemical properties.

Functions: Structural support in biofilms; adhesion to surfaces; protection from desiccation, UV radiation, and antimicrobial agents; binding of metal ions; mediating soil aggregation and nutrient retention in the rhizosphere.

Properties: High molecular weight, hydrophilic, and highly hydrated; their rheological (flow) behavior depends on molecular weight, composition, and ionic strength; they can form gels and thickened solutions, useful as thickeners and stabilizers.

Applications: In the food industry as thickeners and texture modifiers; in pharmaceuticals and cosmetics; in environmental engineering for wastewater treatment, bioremediation, and enhanced oil recovery; in wound care and medical devices. Commercial examples include xanthan gum, gellan gum, dextran, and certain alginates derived from microbial or algal sources.

Safety and research: While many exopolymers are valued product additives, EPS from pathogenic bacteria may contribute to virulence in infections, underscoring the need for appropriate sourcing and safety assessment. Ongoing research aims to tailor EPS properties for specific applications and to understand their role in microbial ecology.