How cAMP and c-di-GMP Signaling Coordinate Pseudomonas aeruginosa Colonization and Infection

Antagonistic Second Messengers Coordinate Pseudomonas aeruginosa Surface Colonization

Bacterial infection requires the efficient colonization of host tissue surfaces. In the human pathogen Pseudomonas aeruginosa, the second messengers cAMP and c-di-GMP regulate surface behaviors and virulence, though how these two pathways coordinate during tissue infection has remained unclear. A published study demonstrates that cAMP and c-di-GMP establish mutually exclusive signaling states at the single-cell level. This mechanism generates distinct subpopulations of motile and surface-attached cells through pathway-specific control of type IV pili.

The Tech TL;DR:

• Single-cell analysis reveals that cAMP and c-di-GMP form mutually exclusive signaling states, splitting bacterial populations into motile and attached groups.
• Initial surface contact spikes c-di-GMP levels, activating FimW for stable bipolar attachment via type IV pili.
• Succeeding states favor cAMP to suppress FimW, trigger FimX-mediated pilus polarization, and drive surface spreading and virulence.

Single-Cell Signaling States Drive Distinct Bacterial Subpopulations

Initial surface contact triggers a local increase in c-di-GMP. This cellular shift activates FimW and drives stable bacterial attachment through bipolar type IV pili formation. Over time, this attached state is progressively replaced by cAMP signaling. The transition inactivates FimW-dependent attachment and induces FimX-mediated type IV pili polarization, driving surface motility and virulence activation.

The resulting signaling transition enforces coexisting subpopulations, where attached cells are gradually displaced by spreading cells. In a human airway tissue model, both type IV pili-mediated adhesion and twitching motility are required for successful host invasion and tissue damage. Researchers propose that this reciprocal cAMP–c-di-GMP signaling mechanism coordinates complementary type IV pili functions to optimize surface colonization and infection.

Experimental Evolution in Airway Environments Selects for Sessile Traits

Complementary findings reported by PMC (pmc.ncbi.nlm.nih.gov) highlight that chronic respiratory tract infections with Pseudomonas aeruginosa involve a process of within-host adaptation. This adaptation produces slow-growing, biofilm-heavy, and reduced-motility phenotypes, which enhance antimicrobial resistance in patients with conditions like cystic fibrosis, non-cystic fibrosis bronchiectasis, and chronic obstructive pulmonary disease. To model this evolution, researchers serially passaged the non-airway-adapted strain PAO1 in media reflecting upper or lower airway environments.

All tested airway environments selected for a loss of twitching motility, increased resistance to multiple antibiotic classes, and a hyper-biofilm phenotype. These traits consistently conferred increased airway colonization potential in an in vivo model. Conditions specific to cystic fibrosis exerted even stronger selective pressures, accelerating the emergence of these phenotypes. The loss of twitching motility mapped directly to mutations in type IV pili genes.

Pathoadaptive Mutations Shape Biofilm Formation and Cyclic-Di-GMP Regulation

Parallel evolutionary routes to increased biofilm formation involve the direct regulation of cyclic-di-GMP signaling. The data identify loss-of-function mutations in the bifA and dipA phosphodiesterase genes, alongside activating mutations in the siaA phosphatase. These genetic adjustments reinforce sessile lifestyles. Upper respiratory environments, particularly paranasal sinuses, act as protective initial niches with limited immune surveillance, supporting a quiescent lifestyle before chronic lung infection establishes.

# Typical experimental passages monitor cyclic-di-GMP regulators:
# Target genes identified in adaptation studies:
MUTATIONS_IDENTIFIED = ["bifA", "dipA", "siaA"]
PHENOTYPE_SHIFT = "Loss of twitching motility + Hyper-biofilm formation"