Alkaline phosphatase LapA regulates quorum sensing–mediated virulence and biofilm formation in Pseudomonas aeruginosa PAO1 under phosphate depletion stress

Abstract

Among various environmental stresses, the depletion of inorganic phosphate, which is an important signaling molecule that modulates virulence production, is notable. In our previous study, we demonstrated that lap A, encoding alkaline phosphatase, plays a key role in Pseudomonas aeruginosa biofilm formation in porcine skin explants, an ex vivo chronic wound model. However, the mechanism by which lap A participates in the virulence and biofilm formation of P. aeruginosa remains unclear. In the present study, the lap A deletion mutant was constructed in P. aeruginosa PAO1, and the phenotypic characterization was assessed. Our data demonstrated that phosphate depletion stress significantly enhanced elastase activity, hemolysis, rhamnolipid production, swarming and swimming motilities, and 3-oxo-C12-homoserine lactone (HSL) production in P. aeruginosa . Moreover, phosphate starvation evidently induced the virulence of P. aeruginosa in Caenorhabditis elegans ( C. elegans ) through fast-kill and slow-kill infections. Deletion of the lap A gene led to broad phenotypic changes, including reduced elastase activity, swimming motility, C4-HSL, and 3-oxo-C12-HSL production, as well as increased chitinase activity and rhamnolipid production under phosphate depletion stress, which was unrelated to C4-HSL. Deletion of the lap A gene also significantly inhibited PAO1 biofilm formation in porcine skin explants by reducing the expression levels of las and rhl quorum sensing systems and extracellular polymeric substance synthesis. Finally, lap A deletion also reduced the virulence of PAO1 in C. elegans in fast-kill and slow-kill infection assays. Thus, the findings suggest that targeting lap A can help control biofilm formation and reduce virulence in nonhealing-infected wounds, where P. aeruginosa is a persistent problem. IMPORTANCE Our previous study demonstrated that the expression of lapA was induced under phosphate depletion conditions, but its roles in virulence and biofilm formation by Pseudomonas aeruginosa remain largely unknown. This study presents a systematic investigation of the roles of lapA in virulence induction and biofilm formation by constructing a lapA-deficient strain with P. aeruginosa PAO1. The results showed that deletion of the lapA gene evidently reduced elastase activity, swimming motility, C4-HSL, and 3-oxo-C12-HSL production, and increased rhamnolipid production under phosphate depletion stress. Moreover, lapA gene deletion inhibited PAO1 biofilm formation in porcine skin explants by reducing the expression levels of las and rhl quorum sensing systems and extracellular polymeric substance synthesis. Finally, lapA gene deletion also reduced the virulence of PAO1 in Caenorhabditis elegans in fast-kill and slow-kill infection assays. This study provides insights into the roles of lapA in modulating P. aeruginosa virulence and biofilm formation under phosphate depletion stress.