Aspergillus Is Inhibited by Pseudomonas aeruginosa Volatiles

Abstract

Background: Pseudomonas aeruginosa (Pa) and Aspergillus fumigatus (Af) compete with each other for nutrients and survival in natural environments, and have been extensively studied because of their intermicrobial interactions in the human microbiome. These are the principal microbes infecting immunocompromised patients and persons with cystic fibrosis, particularly the airways. These intermicrobial studies have largely been conducted in liquid medium or on agar, and thus focus on soluble or diffusible microbial products. Several key inhibitory molecules were defined in such studies. Methods: in the present report, we examine several methodologies which can be conveniently used to study the interaction of microbial volatiles, including capture methods and kinetics. Results: Pa volatiles inhibit Af, and the inhibitory mechanism appears to be the incorporation of the inhibitory molecules into the substrate nourishing the Af, rather than directly onto Af structures. We define by mass spectroscopy some specific volatile Pa products that can inhibit Af. Some of these molecules are selected for interest by the study of gene deletion mutants, producing a few Pa strains that were impaired in inhibition. We presumed the volatiles of these latter strains could be excluded from the search for inhibitors. Conclusion: the Pa inhibition of Af via a gaseous phase could be critical components in their competition, particularly in airways, where more direct contact may not be extensive.

Virus Infection of Aspergillus fumigatus Compromises the Fungus in Intermicrobial Competition

“…At every concentration, the two virus-infected strains were significantly more inhibited than the virus-free. Effect of Pseudomonas volatiles on Aspergillus strains with the assay method and media described (see Methods): In studies with many Pseudomonas laboratory strains and clinical isolates, and several Aspergillus isolates, we find Pseudomonas volatiles to be inhibitory to Aspergillus [18]. The entities responsible appear to be small lipophilic organic molecules.…”

“…It is also probable that virus infection weakens Aspergillus' ability to respond to any stresses, of which iron denial is one. The best evidence for that hypothesis is the differential susceptibility to Pseudomonas volatiles, since small lipophilic organic molecules appear to be the mechanism of such inhibition [18].…”

“…As in the manner of previous studies [18], the effect of Pseudomonas volatiles on Aspergillus growth was assessed by cutting away a 3 mm-wide strip, with a scalpel, out of the agar of an 8 cm diameter TSA agar plate, along a diameter, to separate the plate into 2 semicircular noncontiguous agar halves. The halves were inoculated with 10 microliters of a 10 7 /mL suspension, in RPMI1640 of Pseudomonas, or of Aspergillus conidia, and this co-culture incubated for 72 h, at 37 • C, and then the Aspergillus colony area (πr 2 ) was measured.…”

“…Aspergillus counters the battle for iron with its own siderophores [17]. In a non-liquid air environment, Pseudomonas can also generate volatiles that can inhibit Aspergillus [18]. Presently we studied one aspect of the possible effect of virus infection of Aspergillus fumigatus on this intermicrobial interaction, using tools that have previously been quantitatively standardized.…”

The Rise of Fungi: Evidence on the Global Scale. Old Known Silences or Mysterious Threats to the Planet

“…Interactions and disputes of eukaryotes and prokaryotes, ubiquitous organisms found in many environments and that are part of the human microbiota, were recorded by American researchers [122] in dispute for hosts. The fungus Aspergillus fumigatus and the bacterium Pseudomonas aeruginosa compete with each other for nutrients and survival in natural environments and have been widely studied because of their intermicrobial interactions in the human microbiome.…”