cis -DA-dependent dispersion by Pseudomonas aeruginosa biofilm and identification of cis -DA-sensory protein DspS

Abstract

ABSTRACT Native dispersion, the terminal stage in biofilm development, is characterized by the active escape of cells from a biofilm, leaving behind central voids or hollow structures. However, much of what is known about the dispersion mechanism stems from results obtained in experiments using exogenously added dispersion cues such as nitric oxide (NO) and glutamate. To begin exploring the mechanism of native (endogenous) dispersion by Pseudomonas aeruginosa PAO1 biofilms, we examined the similarities between dispersion exogenously induced with NO and the previously reported native dispersion inducer, cis -2-decenoic acid ( cis -DA), as well as native dispersion. Induction of dispersion with cis -DA was similar to induction with NO, with a significant reduction in cyclic dimeric guanosine monophosphate levels compared with uninduced cells but increased expression of pelA , pslG , endA , and eddA . Of those factors known to contribute to P. aeruginosa biofilm dispersion induced by glutamate and NO, only BdlA , AmrZ, RbdA, and DipA were shown to contribute to dispersion induced with cis -DA. The above factors were also shown to contribute to dispersion when no exogenous inducer was added, as indicated by microcolony void formation, a hallmark of native (endogenous) biofilm dispersion. Interestingly, phosphodiesterase PA2133, the previously reported dispersion sensors (NbdA, MucR, and NicD), and a predicted cis -DA sensor PA4892 played no detectable role in native or cis -DA-dependent dispersion. Instead, we show that cis -DA signal sensing by P. aeruginosa required the sensor/response regulator hybrid DspS (PA4112), with inactivation of dspS impairing cis -DA-induced and native dispersion in two P. aeruginosa strains, PAO1 and PA14. Overall, our findings indicate that while sensing of cis -DA and dispersion cues such as NO and glutamate are distinct, the downstream mechanisms leading to the liberation of biofilm cells and, thus, dispersion rely on a shared pathway. IMPORTANCE Dispersion is an essential stage of the biofilm life cycle resulting in the release of bacteria from a biofilm into the surrounding environment. Dispersion contributes to bacterial survival by relieving overcrowding within a biofilm and allowing dissemination of cells into new habitats for colonization. Thus, dispersion can contribute to biofilm survival as well as disease progression and transmission. Cells dispersed from a biofilm rapidly lose their recalcitrant antimicrobial-tolerant biofilm phenotype and transition to a state that is susceptible to antibiotics. However, much of what is known about this biofilm developmental stage has been inferred from exogenously induced dispersion. Our findings provide the first evidence that native dispersion is coincident with reduced cyclic dimeric guanosine monophosphate levels, while also relying on at least some of the same factors that are central to the environmentally induced dispersion response, namely, BdlA, DipA, RbdA, and AmrZ. Additionally, we demonstrate for the first time that cis-DA signaling to induce dispersion is attributed to the two-component sensor/response regulator DspS, a homolog of the DSF sensor RpfC. Our findings also provide a path toward manipulating the native dispersion response as a novel and highly promising therapeutic intervention.