High-level antibiotic resistance in Pseudomonas aeruginosa biofilm: the ndvB gene is involved in the production of highly glycerol-phosphorylated beta-(1->3)-glucans, which bind aminoglycosides.

Pseudomonas aeruginosa is an opportunistic pathogen that affects immunocompromised individuals and causes life-threatening infections in cystic fibrosis (CF) patients. Colonization of CF lung by P. aeruginosa involves a biofilm mode of growth, which is promoted by the production of exopolysaccharides. These polymers are essential components of the extracellular biofilm matrix. P. aeruginosa possesses several clusters contributing to the formation of the matrix, including the pel or psl genes. In the present study, we identified anionic cyclic glucans produced by P. aeruginosa, which are associated with the matrix of strains PAKDeltaretS and PA14. Their structure has been elucidated using chemical analysis, 1- and 2D nuclear magnetic resonance techniques and mass spectrometry. They belong to a family of cyclic beta-(1-->3)-linked glucans of 12-16 glucose residues with 30-50% of glucose units substituted by 1-phosphoglycerol at O-6. These glucans were also recovered in pel mutant strains, which indicated that their biosynthesis was pel independent. In an effort to understand the biogenesis of these glucans, we analyzed the matrix components of a previously characterized P. aeruginosa PA14 mutant, the PA14::ndvB mutant strain. The ndvB gene was predicted to be involved in the synthesis of perisplasmic glucans, capable of physically interacting with aminoglycoside antibiotics. We revealed that the highly glycerol-phosphorylated beta-(1-->3)-glucans are lacking in the ndvB mutant, and we showed that these glucans are capable of direct binding with the aminoglycoside antibiotic kanamycin. This observation fills a gap in our understanding of the relationship between biofilm, cyclic glucans and high-level antibiotic resistance.