Robaldi, S. A. | bioRxiv Science

bioRxiv2025

Metabolic reshaping drives novel melanin production from tryptophan in a cystic fibrosis Pseudomonas aeruginosa clinical isolate

Pseudomonas aeruginosa is a human opportunistic pathogen, capable of producing a wide range of metabolites, including pyomelanin. This pigment results from alterations in tyrosine catabolism. Melanin synthesis from tryptophan has never been reported in Pseudomonas. In this study, we describe a tryptophan-derived melanin in P. aeruginosa PAH, a strain that was isolated from a fibrocystic patient. PAH produced a brown pigment when grown in LB or L-tryptophan-supplemented media. Structural analysis revealed this pigment was composed by two fractions differing in NaOH solubility: a soluble one consistent of pyomelanin, and an insoluble fraction with a complex structure containing substituted indolic units. A pyomelanin inhibitor enhanced total melanin synthesis, mainly the insoluble fraction, and a tryptophan 2,3-dioxygenase inhibitor decreased pigment formation. Metabolomic profiling identified distinct indolic compounds and low levels of anthranilate in PAH cultures. Genomic and transcriptomic analyses revealed the presence of mutations and downregulation of genes related to pyoverdine biosynthesis. Furthermore, iron supplementation in the culture medium reduced melanin production. Overall, tryptophan arises as a key compound for melanin production in PAH, expanding the diversity of melanins synthesized by this genus. Furthermore, iron deprivation emerges as a critical factor triggering melanin biosynthesis, probably as a survival strategy enabling persistence in the fibrocystic lung environment.

microbiology↗

bioRxiv2023

Fever like temperature impacts on Staphylococcus aureus and Pseudomonas aeruginosa interaction, physiology, and virulence both in vitro and in vivo

BackgroundStaphylococcus aureus and Pseudomonas aeruginosa cause a wide variety of bacterial infections and coinfections, showing a complex interaction that involves the production of different metabolites and metabolic changes. Temperature is a key factor for bacterial survival and virulence and within the host, bacteria could be exposed to an increment in temperature during fever development. We analyzed the previously unexplored effect of fever-like temperatures (39{degrees}C) on S. aureus USA300 and P. aeruginosa PAO1 microaerobic mono- and co-cultures compared with 37{degrees}C, by using RNAseq and physiological assays including in-vivo experiments. ResultsIn general terms both temperature and co-culturing had a strong impact on both PA and SA with the exception of the temperature response of monocultured PA. We studied metabolic and virulence changes on both species. Altered metabolic features at 39{degrees}C included arginine biosynthesis and the periplasmic glucose oxidation in S. aureus and P. aeruginosa monocultures respectively. When PA co-cultures were exposed at 39{degrees}C they upregulated ethanol oxidation related genes along with an increment in organic acid accumulation. Regarding virulence factors, monocultured SA showed an increase in the mRNA expression of the agr operon and hld, pms and pms{beta} genes at 39{degrees}C. Supported by mRNA data, we performed physiological experiments and detected and increment in hemolysis, staphylxantin production and a decrease in biofilm formation at 39{degrees}C. On the side of PA monocultures, we observed increase in extracellular lipase and protease and biofilm formation at 39{degrees}C along with a decrease in motility in correlation with changes observed at mRNA abundance. Additionally, we assessed host-pathogen interaction both in-vitro and in-vivo. S. aureus monocultured at 39{degrees}C showed a decrease in cellular invasion and an increase in IL-8 -but not in IL-6- production by A549 cell line. PA also decreased its cellular invasion when monocultured at 39{degrees}C and did not induce any change in IL-8 or IL-6 production. PA strongly increased cellular invasion when co-cultured at 37{degrees}C and 39{degrees}C. Finally, we observed increased lethality in mice intranasally inoculated with S. aureus monocultures pre-incubated at 39{degrees}C and even higher levels when inoculated with co-cultures. The bacterial burden for P. aeruginosa was higher in liver when the mice were infected with co-cultures previously incubated at 39{degrees}C comparing with 37{degrees}C. ConclusionOur results highlight a relevant change in the virulence of bacterial opportunistic pathogens exposed to fever-like temperatures in presence of competitors, opening new questions related to bacteria-bacteria and host-pathogen interactions and coevolution.

microbiology↗