Deciphering iron uptake and metabolic adaptation in Staphylococcus aureus: new avenues for antimicrobial strategies

Staphylococcus aureus is classified by the World Health Organization as a high-priority pathogen due to its ability to cause severe infections and its increasing antibiotic resistance. Iron is an essential micronutrient for its survival and virulence, and S. aureus has evolved multiple strategies to acquire it from the host environment. The bacterium can utilize both inorganic iron sources and heme iron, the latter being primarily extracted from host hemoglobin (Hb) through the iron-regulated surface determinant (Isd) system. This work focuses on the structural and biochemical characterization of the full-length IsdH Hb receptor, for which only partial and fragmented information was available in the literature. The interaction of IsdH with Hb and the Hb–haptoglobin (Hp) complex was investigated to elucidate its role in heme acquisition. Detailed biochemical analyses were conducted to determine binding stoichiometries, affinities, and heme extraction kinetics. On the structural side, cryo-electron microscopy (cryo-EM) was employed to isolate and characterize preextraction complexes, providing mechanistic insights into the molecular events underlying heme transfer. Furthermore, a screening of small molecules was performed to identify potential inhibitors of complex formation between IsdH and Hb, offering new perspectives for the development of antimicrobial strategies. In parallel, the mechanisms of inorganic iron uptake mediated by the siderophores staphyloferrin A and staphyloferrin B were explored. Metabolomic analyses of S. aureus growths under iron starvation conditions revealed that its metabolic response is strongly influenced by the available carbon source. Studies on mutants impaired in the biosynthesis of staphyloferrins further indicated that the bacterium can dynamically reprogram its metabolism to preserve growth in the absence of these key iron-chelating molecules. Overall, this thesis provides new molecular insights into the iron acquisition strategies of S. aureus, highlighting the remarkable adaptability of its metabolism under nutrient-limiting conditions and contributing to a broader understanding of its pathogenic potential.