BdlA, DipA and Induced Dispersion Contribute to Acute Virulence and Chronic Persistence of Pseudomonas aeruginosa

Abstract

The human pathogen Pseudomonas aeruginosa is capable of causing both acute and chronic infections. Differences in virulence are attributable to the mode of growth: bacteria growing planktonically cause acute infections, while bacteria growing in matrix-enclosed aggregates known as biofilms are associated with chronic, persistent infections. While the contribution of the planktonic and biofilm modes of growth to virulence is now widely accepted, little is known about the role of dispersion in virulence, the active process by which biofilm bacteria switch back to the planktonic mode of growth. Here, we demonstrate that P. aeruginosa dispersed cells display a virulence phenotype distinct from those of planktonic and biofilm cells. While the highest activity of cytotoxic and degradative enzymes capable of breaking down polymeric matrix components was detected in supernatants of planktonic cells, the enzymatic activity of dispersed cell supernatants was similar to that of biofilm supernatants. Supernatants of non-dispersing ΔbdlA biofilms were characterized by a lack of many of the degradative activities. Expression of genes contributing to the virulence of P. aeruginosa was nearly 30-fold reduced in biofilm cells relative to planktonic cells. Gene expression analysis indicated dispersed cells, while dispersing from a biofilm and returning to the single cell lifestyle, to be distinct from both biofilm and planktonic cells, with virulence transcript levels being reduced up to 150-fold compared to planktonic cells. In contrast, virulence gene transcript levels were significantly increased in non-dispersing ΔbdlA and ΔdipA biofilms compared to wild-type planktonic cells. Despite this, bdlA and dipA inactivation, resulting in an inability to disperse in vitro, correlated with reduced pathogenicity and competitiveness in cross-phylum acute virulence models. In contrast, bdlA inactivation rendered P. aeruginosa more persistent upon chronic colonization of the murine lung, overall indicating that dispersion may contribute to both acute and chronic infections.

Origin and Impact of Nitric Oxide in Pseudomonas aeruginosa Biofilms

“…Dispersed cells are physiologically different from planktonic cells, as previously suggested (4,13) and remarked in a recent study showing that freshly dispersed cells (induced by either NO or overexpression of a PDE) are highly virulent and sensitive to iron stress (12). Gene expression patterns are different between planktonic and dispersed cells, but the SNP-(NO donor) and PDEinduced dispersal patterns overlap.…”

“…Dispersed cells are often considered identical to planktonic ones; however, recent reports support earlier findings that dispersed cells represent a specific intermediate state between biofilm and planktonic lifestyles in P. aeruginosa (4,12). This proposal is mainly based on the observation that the physiology and virulence of dispersed cells are highly different from those of biofilm and planktonic ones (12,13). The dispersal phenotype can be achieved and maintained by either the addition of a dispersing agent or the overexpression of a phosphodiesterase (PDE) (see below) (12).…”

Combating Chronic Bacterial Infections by Manipulating Cyclic Nucleotide-Regulated Biofilm Formation

“…The cycling of bacteria between biofilm and planktonic states may be important for the development of disease. For exam-ple, release of bacteria from biofilms has been shown to contribute to the success of P. aeruginosa mouse infections [50]. Biofilm dispersion by NO or glutamate is an active process known to involve a reduction in intracellular c-di-GMP levels.…”

“…Biofilm dispersion by NO or glutamate is an active process known to involve a reduction in intracellular c-di-GMP levels. Several c-di-GMP signaling proteins have been implicated in dispersion; these include the GGDEF-EAL proteins DipA, RbdA, MucR and NbdA [50,51], and the GGDEF proteins NicD [52] and GcbA [53]. How the actions of these different enzymes are coordinated is not fully understood.…”

Living biofouling-resistant membranes as a model for the beneficial use of engineered biofilms

“…their extracellular matrix; for example, upon dispersal, P. aeruginosa uses endoglycosidase PslG to degrade its primary biofilm exopolysaccharide Psl (28) and also degrades extracellular lipids and proteins of the biofilm matrix (29).…”