Quorum sensing regulates a polysaccharide biosynthesis gene to control cell aggregation in <i>Paracoccus denitrificans</i>

Abstract Most biofilm research has centered on a few motile model organisms that form thick biofilms. During dispersal, motile bacteria actively escape through motility; however, non-motile species likely rely on the modulation of adhesive interactions to regulate detachment. In this study we show that the non-motile soil organism Paracoccus denitrificans maintains thin biofilms through constitutive quorum sensing (QS). We show that a LuxI/LuxR-type QS system actively suppresses cell-to-cell adhesion to maintain a thin biofilm architecture, while maintaining a basal level of cell-surface adhesion. We identified a polysaccharide biosynthesis gene, pxm, which is essential for cellular aggregation. Disruption of QS leads to thick biofilm formation with necrotic cores, mediated by Pxm-dependent production. Using microfluidic chambers, we examined interactions between Pxm and BapA adhesion factors under varying spatial confinement. Our findings reveal that QS-dependent suppression of adhesion factors enables P. denitrificans to form thin, loosely connected biofilms that promote nutrient access and dispersal, providing an ecological advantage in spatially confined environments such as soil or aquatic sediments.