The essential role of hydrophobic interaction within extracellular polymeric substances in auto-aggregation of P. stutzeri strain XL-2.

To enrich the understanding of bio-aggregates formation, the mechanism of auto-aggregation is one of the concerns in wastewater treatment. The auto-aggregation ability by P. stutzeri strain XL-2 was mainly attributed to the self-secretion of extracellular polymeric substances (EPS). A comprehensive correlation analysis indicates that hydrophobic interaction within EPS played essential roles in auto-aggregation. To give insights into the underlying mechanisms, tightly bound EPS (TB-EPS), loosely bound EPS (LB-EPS) and soluble EPS (S-EPS) were characterized by colorimetry, hydrophobicity, enzymatic hydrolysis, FT-IR spectroscopy and XPS analysis, showing that proteins in TB-EPS comprised a high proportion of hydrophobic carbon-containing (C-containing) functional groups. Further amino acids analysis revealed that these C-containing functional groups might derive from the hydrophobic R groups of amino acids, which significantly affected the surface hydrophobicity of proteins in TB-EPS and thus promoted the auto-aggregation of strain XL-2. This work provides an in-deep understanding of the auto-aggregation mechanism by strain XL-2, which may enrich the understanding of microbial aggregates formation and lead to further application of strain XL-2 in wastewater treatment processes. [Display omitted] • P. stutzeri strain XL-2 presented high auto-aggregation ability. • Hydrophobic interaction of EPS served essential role in auto-aggregation. • Proteins of TB-EPS mainly contributed to the hydrophobicity. • Hydrophobic functional groups mainly presented in proteins of TB-EPS. • Hydrophobic functional groups might derive from hydrophobic R groups of amino acids. [ABSTRACT FROM AUTHOR]