Rhizobacterial Exopolysaccharides in Soil–Plant Systems: Molecular Mechanisms, Engineering Approaches, and Translational Challenges

Plant productivity has become increasingly affected by various abiotic and biotic factors such as drought, salinity, metal toxicity, heat/cold stresses, and pathogen pressure that disrupt soil-plant interactions. Plant growth-promoting rhizobacteria (PGPR)-secreted exopolysaccharides (EPSs) play a significant role in maintaining rhizosphere stability through promoting soil aggregation, increasing the soil water retention capacity, and proper ion management. In addition, EPSs provide extracellular binding sites for toxic metals and facilitate the formation of stress-tolerant biofilms. Production of EPSs is under the strict control of sophisticated regulatory systems, linking environmental conditions and adaptive mechanisms at the genetic level. Novel advancements in omics and genome editing techniques could be used in the development of improved EPS-secreting strains with enhanced stress-resistance capabilities. Potential applications include PGPR formulations for seed coating, bioinoculants, and soil treatments; however, strain heterogeneity and environmental variability represent important challenges.