Siderophores are small molecules that bind iron with high affinity, enabling microorganisms to acquire iron from their environment. Iron is essential for many metabolic processes, but in most environments, iron is in the form of Fe(III), which is not easily absorbed by cells. Siderophores help microorganisms overcome this limitation by forming stable complexes with Fe(III), which can then be taken up by specific transporters or reduced to Fe(II) for use in cellular processes. Siderophore-based iron acquisition is a widespread strategy among bacteria, fungi, and even plants, and it plays a critical role in pathogen survival and virulence. Siderophores are classified based on the type of ligand that coordinates with Fe(III), including catecholates, hydroxamates, and carboxylates. These molecules are synthesized by microorganisms under iron-limiting conditions and are secreted into the environment to bind Fe(III). The bound iron can then be taken up by specific transporters or reduced to Fe(II) by reductases, allowing the cell to utilize the iron for growth and metabolic functions. Some microorganisms can also utilize exogenous siderophores produced by other organisms, which provides an additional source of iron. The regulation of siderophore biosynthesis and iron acquisition is tightly controlled by various transcriptional and posttranscriptional mechanisms. In bacteria, the ferric uptake repressor (Fur) is a key regulator that controls the expression of genes involved in iron acquisition and homeostasis. Other regulators, such as DtxR and AraC-type regulators, also play important roles in sensing and responding to changes in iron availability. In yeast, the transcriptional activators Aft1p and Aft2p regulate iron homeostasis by controlling the expression of genes involved in iron uptake and storage. Siderophore biosynthesis is often catalyzed by nonribosomal peptide synthetases (NRPSs), which are large, multi-enzyme complexes that assemble amino acids and other precursors into siderophore molecules. The biosynthesis of siderophores can also occur through NRPS-independent pathways, which involve a variety of enzymatic activities. The final step in siderophore biosynthesis often involves cyclization reactions that form macrocyclic structures, which are essential for the stability and function of the siderophore. Siderophore-based iron acquisition is a critical strategy for many pathogens, allowing them to survive in environments where iron is scarce. However, this strategy is also a target for host defenses, which use siderophore-binding proteins to sequester iron and prevent its availability to pathogens. Understanding the mechanisms of siderophore biosynthesis, secretion, and uptake is essential for developing new strategies to control pathogen growth and infection.Siderophores are small molecules that bind iron with high affinity, enabling microorganisms to acquire iron from their environment. Iron is essential for many metabolic processes, but in most environments, iron is in the form of Fe(III), which is not easily absorbed by cells. Siderophores help microorganisms overcome this limitation by forming stable complexes with Fe(III), which can then be taken up by specific transporters or reduced to Fe(II) for use in cellular processes. Siderophore-based iron acquisition is a widespread strategy among bacteria, fungi, and even plants, and it plays a critical role in pathogen survival and virulence. Siderophores are classified based on the type of ligand that coordinates with Fe(III), including catecholates, hydroxamates, and carboxylates. These molecules are synthesized by microorganisms under iron-limiting conditions and are secreted into the environment to bind Fe(III). The bound iron can then be taken up by specific transporters or reduced to Fe(II) by reductases, allowing the cell to utilize the iron for growth and metabolic functions. Some microorganisms can also utilize exogenous siderophores produced by other organisms, which provides an additional source of iron. The regulation of siderophore biosynthesis and iron acquisition is tightly controlled by various transcriptional and posttranscriptional mechanisms. In bacteria, the ferric uptake repressor (Fur) is a key regulator that controls the expression of genes involved in iron acquisition and homeostasis. Other regulators, such as DtxR and AraC-type regulators, also play important roles in sensing and responding to changes in iron availability. In yeast, the transcriptional activators Aft1p and Aft2p regulate iron homeostasis by controlling the expression of genes involved in iron uptake and storage. Siderophore biosynthesis is often catalyzed by nonribosomal peptide synthetases (NRPSs), which are large, multi-enzyme complexes that assemble amino acids and other precursors into siderophore molecules. The biosynthesis of siderophores can also occur through NRPS-independent pathways, which involve a variety of enzymatic activities. The final step in siderophore biosynthesis often involves cyclization reactions that form macrocyclic structures, which are essential for the stability and function of the siderophore. Siderophore-based iron acquisition is a critical strategy for many pathogens, allowing them to survive in environments where iron is scarce. However, this strategy is also a target for host defenses, which use siderophore-binding proteins to sequester iron and prevent its availability to pathogens. Understanding the mechanisms of siderophore biosynthesis, secretion, and uptake is essential for developing new strategies to control pathogen growth and infection.