Iron deficiency leads to blockage of oxygen transfer in culture of Pseudomonas aeruginosa PAO1

SUMMARY Pseudomonas aeruginosa PAO1 was recently reported to exhibit an unusual property of dramatically reducing the efficiency of oxygen transfer from the gas phase into the liquid phase and thus causing oxygen limitation in the culture. In this work, we show that iron concentration in the culture plays a crucial role in evoking this phenomenon. The physiological responses of two P. aeruginosa PAO1 strains (NCCB 2452 and ATCC 15692) were examined in growth media with varied iron concentrations. In a computer-controlled bioreactor cultivation system for the control of dissolved oxygen tension (pO 2), a strong correlation between the exhaustion of iron and the onset of oxygen limitation was observed. The oxygen transfer rate of the culture, characterized by the volumetric oxygen transfer coefficient k L a, significantly decreased under iron-limited conditions. The reduction of oxygen transfer rate and the subsequent oxygen limitation triggered by iron deficiency represent a new and efficient way for P. aeruginosa PAO1 to adapt to growth conditions of iron limitation. Under these conditions the two P. aeruginosa PAO1 strains grew equally well as under iron-sufficient aerobic conditions. Furthermore, the secretion of proteins into the culture medium was strongly enhanced. The formation of the virulence factor elastase und the iron chelators pyoverdine and pyochelin (siderophores) also significantly increased under iron-limited conditions. These results have implications for lung infection of cystic fibrosis patients by P. aeruginosa in view of the prevalence of iron limitation at the site of infection and the respiratory failure leading to death.