Interactions between Aspergillus fumigatus and Pulmonary Bacteria: Current State of the Field, New Data, and Future Perspective

Aspergillus fumigatus and Pseudomonas aeruginosa are central fungal and bacterial members of the pulmonary microbiota. The interactions between A. fumigatus and P. aeruginosa have only just begun to be explored. A balance between inhibitory and stimulatory effects on fungal growth was observed in mixed A. fumigatus–P. aeruginosa cultures. Negative interactions have been seen for homoserine-lactones, pyoverdine and pyochelin resulting from iron starvation and intracellular inhibitory reactive oxidant production. In contrast, several types of positive interactions were recognized. Dirhamnolipids resulted in the production of a thick fungal cell wall, allowing the fungus to resist stress. Phenazines and pyochelin favor iron uptake for the fungus. A. fumigatus is able to use bacterial volatiles to promote its growth. The immune response is also differentially regulated by co-infections.