Acidic Stress Induces Proteomic Reprogramming and Virulence-Associated Adaptation in Paracoccidioides brasiliensis

Paracoccidioidomycosis (PCM) is a neglected systemic mycosis whose etiologic agents must adapt to acidic host niches such as phagolysosomes. Here, we used quantitative liquid chromatography-tandem mass spectrometry (LC-MS/MS)-based proteomics to define the response of Paracoccidioides brasiliensis to acidic stress (pH 4.5) versus control pH (6.5) after 5 and 24 h. We identified and quantified 4374 proteins, including 327 and 722 differentially abundant proteins at 5 and 24 h, respectively, revealing time-dependent proteomic reprogramming. Enrichment analyses highlighted proteolysis, protein metabolism, organonitrogen metabolism, MAPK- and SNF1-like signaling, central carbon metabolism, tyrosine metabolism, and ergosterol biosynthesis as major acid-responsive processes. Complementary assays showed pH-dependent extracellular proteolytic activity, increased adhesion to A549 pulmonary epithelial cells, and dynamic ergosterol remodeling. The proteomic data further indicated increased abundance of moonlighting proteins linked to adhesion and metabolic enzymes associated with ATP generation and melanin precursor production. Together, these findings indicate that P. brasiliensis adapts to acidic environments through coordinated regulation of proteostasis, metabolism, signaling, host-cell interaction, and membrane homeostasis, supporting survival and virulence potential in acidic host microenvironments.