Altered Pseudomonas Strategies to Inhibit Surface Aspergillus Colonies
Gabriele Sass1, Hasan Nazik1, Paulami Chatterjee1
1Infectious Disease Research Laboratory, San Jose, CA, United States.
Abstract:
Pseudomonas aeruginosa and Aspergillus fumigatus infections frequently co-localize in lungs of immunocompromised patients and individuals with cystic fibrosis (CF). The antifungal activity of P. aeruginosa has been described for its filtrates. Pyoverdine and pyocyanin are the principal antifungal P. aeruginosa molecules active against A. fumigatus biofilm metabolism present in iron-limited or iron-replete planktonic P. aeruginosa culture filtrates, respectively. Using various P. aeruginosa laboratory wild-type strains (PA14, PAO1, PAK), we found antifungal activity against Aspergillus colonies on agar. Comparing 36 PA14 and 7 PAO1 mutants, we found that mutants lacking both major siderophores, pyoverdine and pyochelin, display higher antifungal activity on agar than their wild types, while quorum sensing mutants lost antifungal activity. Addition of ferric iron, but not calcium or magnesium, reduced the antifungal effects of P. aeruginosa on agar, whereas iron-poor agar enhanced antifungal effects. Antifungal activity on agar was mediated by PQS and HHQ, via MvfR. Among the MvfR downstream factors, rhamnolipids and elastase were produced in larger quantities by pyoverdine-pyochelin double mutants and showed antifungal activity on agar. In summary, antifungal factors produced by P. aeruginosa on agar differ from those produced by bacteria grown in liquid cultures, are dependent on quorum sensing, and are downregulated by the availability of ferric iron. Rhamnolipids and elastase seem to be major mediators of Pseudomonas' antifungal activity on a solid surface.
Insights
Pseudomonas aeruginosa exhibits antifungal properties against Aspergillus fumigatus on agar surfaces. This activity is mediated by quorum sensing and influenced by iron availability, with rhamnolipids and elastase being key factors.
Area of Science:
- Microbiology
- Medical Mycology
- Infectious Diseases
Background:
- Co-infections of Pseudomonas aeruginosa and Aspergillus fumigatus are common in immunocompromised patients and cystic fibrosis (CF) individuals.
- P. aeruginosa exhibits antifungal activity, with pyoverdine and pyocyanin identified as key molecules in liquid culture filtrates against A. fumigatus biofilms.
Purpose of the Study:
- To investigate the antifungal activity of P. aeruginosa against Aspergillus colonies on agar surfaces.
- To identify the specific molecules and pathways involved in P. aeruginosa's antifungal activity on solid media.
Main Methods:
- Utilized various P. aeruginosa laboratory wild-type strains (PA14, PAO1, PAK) and compared 36 PA14 and 7 PAO1 mutants.
- Assessed antifungal activity on agar plates and analyzed the impact of iron availability (ferric, calcium, magnesium).
- Investigated the role of quorum sensing systems (PQS, HHQ, MvfR) and downstream factors like rhamnolipids and elastase.
Main Results:
- Mutants lacking both pyoverdine and pyochelin showed enhanced antifungal activity on agar compared to wild-type strains.
- Quorum sensing mutants exhibited a loss of antifungal activity.
- Ferric iron reduced antifungal effects, while iron-poor agar enhanced them.
- Rhamnolipids and elastase, produced in higher quantities by double mutants, demonstrated antifungal activity on agar.
Conclusions:
- Antifungal factors produced by P. aeruginosa on agar differ from those in liquid cultures.
- Quorum sensing is essential for P. aeruginosa's antifungal activity on agar, and this activity is downregulated by ferric iron.
- Rhamnolipids and elastase are identified as major mediators of Pseudomonas's antifungal activity on solid surfaces.
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