Pseudomonas aeruginosa inhibits Rhizopus microsporus germination via the sequestration of iron

C Kousser, K Voelz, RA Hall

Author address: 

Institute of Microbiology and Infection, School of Biosciences, University of Birmingham, UK


Background: Within the human body, microorganisms reside as part of a complex and varied ecosystem, where they rarely exist in isolation. Therefore, bacteria and fungi have co-evolved to develop elaborate and intricate relationships, utilising both physical and chemical communication mechanisms. Mucormycetes are spore-forming fungi belonging to the order Mucorales and are the causative agents of potentially fatal mucormycosis in immunocompromised individuals. Key to the pathogenesis of mucormycetes is the ability to swell and germinate leading to penetration of the surrounding tissues, angioinvasion, vessel thrombosis, and tissue necrosis. Mucormycete spores are found ubiquitously in the environment and in wounds, where they encounter a myriad of bacterial and fungal species including Pseudomonas aeruginosa. Purpose: Early diagnosis is key to successfully treating mucormycosis, and understanding the interplay between microorganisms which they may interact is important in developing targeted diagnostic and therapeutic methods. It is currently unknown whether mucormycetes participate in polymicrobial relationships, and if so, how this affects the pathogenesis, disease progression, and overall patient prognosis. This project aims to analyse the nature of the relationships between these fungal pathogens and the microorganisms they may encounter. Methods: Resting R. microsporus spores were exposed to both sterile supernatant from overnight cultures of P. aeruginosa and live bacteria. Live-cell imaging and absorbance measurements were used to identify the ability of spores to germinate under these conditions. Exogenous iron was added to these mixed cultures to observe the ability to rescue, and molecular approaches were utilised. Results: We show that culture supernatants from P. aeruginosa and live bacteria are able to inhibit the germination of Rhizopus microsporus spores. This inhibition of germination was not due to the presence of quorum sensing molecules or toxins, but was instead due to iron restriction, as addition of exogenous iron restored germination. Conclusion: We hypothesise that P. aeruginosa secretes iron siderophores, which sequester the available iron, inhibiting fungal germination. Therefore, treatment of P. aeruginosa in trauma wounds could result in the release of this inhibition of germination, leaving the patient prone to an underlying fungal infection.

abstract No: 


Full conference title: 

The 8th Advances Against Aspergillus, Lisbon Conference Center, Lisbon, Portugal
    • AAA 8th (2018)