Gene expression of Pseudomonas aeruginosa in a mucin-containing synthetic growth medium mimicking cystic fibrosis lung sputum.

Pseudomonas aeruginosa airway infection is the leading cause of morbidity and mortality in cystic fibrosis (CF) patients. Various in vitro models have been developed to study P. aeruginosa pathobiology in the CF lung. In this study we produced a modified artificial-sputum medium (ASMDM) more closely resembling CF sputum than previous models, and extended previous work by using strain PAO1 arrays to examine the global transcription profiles of P. aeruginosa strain UCBPP-PA14 under early exponential-phase and stationary-phase growth. In early exponential phase, 38/39 nutrition-related genes were upregulated in line with data from previous in vitro models using UCBPP-PA14. Additionally, 23 type III secretion system (T3SS) genes, several anaerobic respiration genes and 24 quorum-sensing (QS)-related genes were upregulated in ASMDM, suggesting enhanced virulence factor expression and priming for anaerobic growth and biofilm formation. Under stationary phase growth in ASMDM, macroscopic clumps resembling microcolonies were evident in UCBPP-PA14 and CF strains, and over 40 potentially important genes were differentially expressed relative to stationary-phase growth in Luria broth. Most notably, QS-related and T3SS genes were downregulated in ASMDM, and iron-acquisition and assimilatory nitrate reductase genes were upregulated, simulating the iron-depleted, microaerophilic/anaerobic environment of CF sputum. ASMDM thus appears to be highly suitable for gene expression studies of P. aeruginosa in CF.