Dispersion and the Biofilm Matrix of Pseudomonas aeruginosa

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PROJECT SUMMARY Antimicrobial resistant, chronic infections are one of the greatest challenges facing our society today. This problem is so significant that the World Health Organization named antibiotic resistance as one of the top ten threats to global health in 2019. More than 80% of these infections have been attributed to the remarkable capabilities of bacteria to form biofilms, communities of microorganisms encased in a protective matrix of extracellular polymeric substance, that are irresponsive to antimicrobials. Pseudomonas aeruginosa is the 2nd leading cause of these infections, and routinely the most common cause of fatalities in patients with nosocomial infections. Dispersion is considered a promising avenue open for biofilm control, by assisting in resolving biofilm- associated infections. This is because dispersion is an active, regulated process by which bacteria escape biofilms as free-living cells that are once again susceptible to antimicrobials, with dispersion thus capable of enhancing the efficacy of antibiotics. However, while dispersion cue sensing by P. aeruginosa and how these cues are translated into the modulation of the c-di-GMP pool has been elucidated in great detail, little is known about downstream events enabling P. aeruginosa to egress from the biofilm, the contribution of c-di-GMP, or factors driving the virulence switch by dispersed cells. Using RNA-seq, we have identified genes that are unique to dispersed cells (termed “dispersion regulon”) and contribute to the phenotype ascribed to dispersed cells including drug susceptibility, virulence, and matrix degradation. We confirmed factors involved in matrix degradation and the reinforcement of the biofilm matrix to contribute to dispersion. However, no obvious matrix degrading enzymes have been thus far identified which target the matrix EPS Psl, suggesting differences in matrix degradation and dispersion by different classes of matrix-producing P. aeruginosa strains. Moreover, our findings suggest that the modulation of c-di-GMP is not sufficient to induce dispersion and only explains some of the phenotypes of dispersed cells. Based on these premises, we hypothesize that dispersion and dispersion- related phenotypes require c-di-GMP-(in)dependent pathways including genes and gene functions involved in matrix degradation that likely differ amongst the classes of matrix utilization. The goal of this project is to elucidate the signaling and regulatory events leading to dispersion including matrix-degradation, and dispersed cells adopting an acute virulence phenotype. We will therefore elucidate in Aim 1 pathways leading to dispersion and dispersion-related phenotypes in vitro and in vivo, and spatio-temporally assess the fate of matrix components during dispersion in Aim 2. Aim 3 aims at determining whether the dispersion and factors required for dispersion are similar or are different in non-mucoid clinical isolates representing 4 different matrix classes. We anticipate our findings to not only contribute to understanding infection but also assist in guiding the development of dispersion towards an adjunctive therapy for biofilm control.