Microbial extracellular polymeric substances (EPS) in soil: From interfacial behaviour to ecological multifunctionality

Abstract Extracellular polymeric substances (EPS) are high molecular weight polymers that microorganisms secrete into their extracellular environment. EPS serves as the carrier of the structural integrity of microbial biofilms, determining the physicochemical properties and the functional complexity of biofilms. EPS creates an ideal environment for interfacial reactions and nutrient trapping around microbial cells, while also acting as a buffer zone against environmental stresses. EPS in soil can contribute to soil health through its own properties such as adhesion, hygroscopicity and complexing ability. Here, we first introduce the concept, components, properties and controlled factors of EPS in the soil environment, and outline current advances in extraction methods and characterization techniques for soil EPS. EPS form a dynamic biophysical-chemical interface between microbes and the soil matrix. We explore the role of EPS in the colonization and survival of microorganisms, aggregation and weathering of soil minerals, and cross-linking with soil organic matter. We then summarize the soil ecological functions of microbial EPS: 1) promoting aggregate formation and stabilization; 2) enhancing water retention and holding capacity; 3) mediating nutrient storage and trapping; and 4) regulating contaminant sequestration and transformation. Finally, we propose several future research interests for microbial EPS in soil, thereby calling for more attention and research on microbial EPS and its functions in soil ecosystems, and exploring their potential applications in the development of environment-friendly agriculture.