Pseudomonas aeruginosa-Derived Volatile Sulfur Compounds Promote Distal Aspergillus fumigatus Growth and a Synergistic Pathogen-Pathogen Interaction That Increases Pathogenicity in Co-infection

Abstract

Pathogen-pathogen interactions in polymicrobial infections are known to directly impact, often to worsen, disease outcomes. For example, co-infection with Pseudomonas aeruginosa and Aspergillus fumigatus, respectively the most common bacterial and fungal pathogens isolated from cystic fibrosis (CF) airways, leads to a worsened prognosis. Recent studies of in vitro microbial cross-talk demonstrated that P. aeruginosa-derived volatile sulfur compounds (VSCs) can promote A. fumigatus growth in vitro. However, the mechanistic basis of such cross-talk and its physiological relevance during co-infection remains unknown. In this study we combine genetic approaches and GC-MS-mediated volatile analysis to show that A. fumigatus assimilates VSCs via cysteine (CysB)- or homocysteine (CysD)-synthase. This process is essential for utilization of VSCs as sulfur sources, since P. aeruginosa-derived VSCs trigger growth of A. fumigatus wild-type, but not of a ΔcysBΔcysD mutant, on sulfur-limiting media. P. aeruginosa produces VSCs when infecting Galleria mellonella and co-infection with A. fumigatus in this model results in a synergistic increase in mortality and of fungal and bacterial burdens. Interestingly, the increment in mortality is much greater with the A. fumigatus wild-type than with the ΔcysBΔcysD mutant. Therefore, A. fumigatus’ ability to assimilate P. aeruginosa derived VSCs significantly triggers a synergistic association that increases the pathobiology of infection. Finally, we show that P. aeruginosa can promote fungal growth when growing on substrates that resemble the lung environment, which suggests that this volatile based synergism is likely to occur during co-infection of the human respiratory airways.

Aspergillus Is Inhibited by Pseudomonas aeruginosa Volatiles

“…There was no inhibition of Af by any putative volatiles from any agar, or from the plastic plate itself. In addition, the comparison of Af with the Pa plates in prior experiments with all the controls with no Pa now mentioned did not indicate any stimulation by Pa of Af growth, in contrast to what has been reported [57,62].…”

“…Because of reports [57,62] that Pa volatiles could stimulate Af, we performed tests with our system. The investigators [57] kindly donated the Af strain, CBS 144-89, used in their studies.…”

“…We have described above that LB agar, one of the media used by these investigators [57,62], does not by itself produce volatiles stimulating Af growth. In another experiment, we compared the Af and Pa growth on both TSA and LB agar, the three Pa described in the above experiment, and CBS 144-89, but used the "plate-in-plate" method described by the investigators [57], including the micro-organism inoculum sizes they used.…”

The Gut-Lung Axis in Health and Respiratory Diseases: A Place for Inter-Organ and Inter-Kingdom Crosstalks

“…Synergistic interactions have been documented between Candida and Streptococcus, such as stimulation of Streptococcus growth by Candida, increasing biofilm formation, or enhancement of the Candida pathogenicity by Streptococcus (Diaz et al, 2012;Xu et al, 2014). In vitro studies exhibited an increased growth of Aspergillus fumigatus in presence of Pseudomonas aeruginosa, due to the mold's ability in to assimilate P. aeruginosa-derived volatile sulfur compounds (Briard et al, 2019;Scott et al, 2019). However, the lung microbiota modulation is not limited to local inter-kingdom crosstalk and also depends on inter-compartment crosstalk between the gut and lungs.…”

Targeting methionine synthase in a fungal pathogen causes a metabolic imbalance that impacts cell energetics, growth and virulence

“…1A). As we had previously observed (26), to rescue fully metF's growth the media had to be supplemented with methionine and other amino acids, as the folate cycle is necessary for the interconversion of serine and glycine and plays a role in histidine and aromatic amino acid metabolism (27,28).…”