WS07.03 A long-term study of Pseudomonas aeruginosa early patient isolate adaptation to the hypoxic environment

Abstract

Pseudomonas aeruginosa is an opportunistic bacterial pathogen which causes chronic lung infections in people with cystic fibrosis (CF) and is a major contributor to morbidity and mortality. Despite this, the mechanism driving its adaptation towards chronic colonisation in the CF lung is not yet fully understood. This work focuses on the adaptations of P. aeruginosa to hypoxia, one of the important environmental pressures present in the lung. Long term hypoxia has yet to be examined as a driver of adaptation towards the persistence of this bacterium in CF patients. We have studied the effect of long term adaptation to 6% oxygen for up to 28 days. Interestingly, distinctive colony morphotypes developed throughout the experiments, including small colony variants (SCV). One of the observed morphotypes appeared exclusively under low-oxygen pressure. Importantly, the colonies with visibly different morphologies were more common in hypoxia adapted cultures, comprising up to 98% of the population, while they never exceeded 35% in normoxia adapted cultures. Proteomic analysis showed changes in the abundance of over 700 proteins within 5 days of adaptation, including those involved in respiration and carbon metabolism, quorum sensing and phenazine biosynthesis. Interestingly, comparable changes in several pathways were consistent across both conditions while phenotype differences in motility, pyocyanin production, and protease production between the different colony morphotypes in samples taken over time were observed. Both the SCV and the normal colony variants (NCV) from the hypoxia adapted strains showed decreases in motility, pyocyanin production and protease production. A Congo red assay showed increased exopolysaccharide production in both hypoxia adapted SCV and NCVs. Overall, these results confirm that hypoxia indeed promotes the appearance of many phenotypes in P. aeruginosa that are associated with persistence in the lung and with poor patient outcomes.