Contribution of Cell Elongation to the Biofilm Formation of Pseudomonas aeruginosa during Anaerobic Respiration

Pseudomonas aeruginosa, a gram-negative bacterium of clinical importance, forms more robust biofilm during anaerobic respiration, a mode of growth presumed to occur in abnormally thickened mucus layer lining the cystic fibrosis (CF) patient airway. However, molecular basis behind this anaerobiosis-triggered robust biofilm formation is not clearly defined yet. Here, we identified a morphological change naturally accompanied by anaerobic respiration in P. aeruginosa and investigated its effect on the biofilm formation in vitro. A standard laboratory strain, PAO1 was highly elongated during anaerobic respiration compared with bacteria grown aerobically. Microscopic analysis demonstrated that cell elongation likely occurred as a consequence of defective cell division. Cell elongation was dependent on the presence of nitrite reductase (NIR) that reduces nitrite (NO2−) to nitric oxide (NO) and was repressed in PAO1 in the presence of carboxy-PTIO, a NO antagonist, demonstrating that cell elongation involves a process to respond to NO, a spontaneous byproduct of the anaerobic respiration. Importantly, the non-elongated NIR-deficient mutant failed to form biofilm, while a mutant of nitrate reductase (NAR) and wild type PAO1, both of which were highly elongated, formed robust biofilm. Taken together, our data reveal a role of previously undescribed cell biological event in P. aeruginosa biofilm formation and suggest NIR as a key player involved in such process

Increased airway iron as a potential factor in the persistence of Pseudomonas aeruginosa infection in cystic fibrosis

Iron availability is critical to many bacteria and increased iron has been described in airway secretions in cystic fibrosis (CF), The main aim of the present study was to assess the relationship between iron in CF sputum and the quantitative bacterial burden, Iron, ferritin and total cell counts (TCC) were assessed in sputum samples obtained from 15 clinically stable CF patients chronically infected with Pseudomonas aeruginosa, Sputum samples were also obtained at the commencement of episodes of acute exacerbation in 10 subjects and analyses were repeated in six of these exacerbation cases after t.v. antibiotic treatment The relationship between iron indices and the presence of P. aeruginosa, as well as total anaerobic bacterial load, was determined. Sputum was also obtained from 10 CF patients with no evidence of infection with P. aerug/nosa and 11 normal healthy controls, Sputum iron, ferritin and TCC were significantly elevated in aU CF patients, even in those not infected with P. aerug/nosa, compared with healthy controls, There was a strong positive relationship between sputum iron and P, aemg/nosa in clinically stable patients, but not in samples obtained during an acute exacerbation. There was no relationship between sputum iron and anaerobic bacterial load. Antibiotic treatment significantly reduced sputum TCC and anaerobic bacterial load, but not iron, ferritin or the presence of P. aemg/nosa during an exacerbation. In conclusion, the present study suggests that increased airway iron may be important to Pseudomonas aemg/nosa persistence in cystic fibrosis

Comparing the microbiota of the cystic fibrosis lung and human gut

Peer reviewedPublisher PD