Complementary functionalities of extracellular polymeric substances, adhesion ability and hydrophobicity in Pseudomonas isolates may help the selection of strategically advantageous microbial inoculants

Microbial persistence and colonization in the rhizosphere rely on traits that control how cells attach, interact, and organize into biofilms. Among these traits, extracellular polymeric substances (EPS), cell surface hydrophobicity, and adhesion play central roles in the early stages of root surface colonization. Here, we examined 48 isolates of the Pseudomonas fluorescens group associated with Tuber borchii fruiting bodies to explore the relationships among bound and released EPS fractions, hydrophobicity and adhesion ability. All experiments were carried out under controlled in vitro conditions using polystyrene as an abiotic model that mimics the hydrophobic interfaces occurring in soil–root environments. EPS fractions were quantified by Congo red and phenol–sulfuric acid assays, while surface hydrophobicity and adhesion were determined through xylene partitioning and crystal violet staining. The isolates exhibited wide phenotypic variability. Bound EPS showed a strong negative relationship with both hydrophobicity and adhesion, while hydrophobicity was positively associated with adhesion strength. Regression models confirmed that bound EPS and hydrophobicity independently modulate the adhesion response. These findings suggest that thick, hydrated EPS layers can hinder early attachment, while thinner EPS coatings enhance cell–surface interactions. Understanding this functional trade-off provides a basis for the informed selection of microbial inoculants, combining stable biofilm formers with highly adhesive strains to improve persistence and colonization efficiency in rhizosphere environments.