Exploring aggregation genes in a P. aeruginosa chronic infection model

Area of Science:

• Microbiology
• Genetics
• Infectious Diseases

Background:

• Bacterial aggregates, particularly Pseudomonas aeruginosa (Pa), are significant in chronic infections like cystic fibrosis (CF).
• Pa aggregates in CF sputum are small (~10-1,000 cells), and their formation mechanisms are poorly understood.
• Existing in vitro models do not fully replicate the in vivo environment of CF sputum.

Purpose of the Study:

• To identify genes essential and unique to Pa aggregate formation in a synthetic CF sputum medium (SCFM2).
• To understand the role of specific genes in Pa aggregation phenotypes.
• To explore cooperative interactions in Pa aggregate development.

Main Methods:

• Cultured Pa strain PAO1 in synthetic CF sputum media (SCFM2) and Luria-Bertani (LB) broth, with and without mucin.
• Utilized RNA sequencing (RNA-seq) to identify differentially expressed genes in response to mucin.
• Employed high-resolution microscopy to analyze aggregate formation in gene mutants.
• Conducted predictive modeling and co-culture experiments to understand gene function and interactions.

Main Results:

• Identified 13 significantly differentially expressed genes in SCFM2 with mucin, many downregulated and encoding hypothetical proteins.
• Observed distinct spatial phenotypes (normal, entropic, impaired) in mutants, with no completely planktonic mutants.
• Linked prioritized genes to metabolic shifts, iron acquisition, surface modification, and quorum sensing.
• Co-culture experiments revealed spatial heterogeneity and rescue of mutant phenotypes by wild-type Pa, indicating cooperative interactions.

Conclusions:

• This study elucidates genes and pathways critical for Pa aggregation in CF-like environments.
• Identified unique genetic factors contributing to Pa aggregate formation.
• Provides foundational insights for developing novel therapeutic strategies targeting Pa aggregate-specific pathways in CF infections.