ABSTRACT
Quorum sensing (QS) is a cell density–dependent signaling system mediated by chemical autoinducer molecules produced by bacteria. QS plays an important role in biofilm formation and accessing the nutrients, make more favorable environmental niches, and also regulate multicellular behaviors, for instance, bioluminescence, cell competency, horizontal gene transfer, virulence, motility, siderophore formation, production of antibiotics transfer of conjugative plasmids, sporulation, antimicrobial peptide synthesis, and regulation of virulence and other secondary metabolites. Siderophores are good iron chelating agents and are useful for the phytoremediation of heavy metal and xenobiotic compound remediation. Siderophores are classified by the ligands used to chelate the ferric iron. The major groups of siderophores include hydroxamates, catecholates (phenolates), carboxylates (e.g., derivatives of citric acid), and mixed types. During intracellular iron deficiency conditions, microorganisms secrete siderophores into the environment to scavenge iron. There are two pathways involved in the synthesis of siderophores: (1) Dependent on nonribosomal peptide synthatases (NRPS) and (2) independent of NRPS. Siderophores and iron complexes enter in the cell either through the ABC transporters (ferrichrome and ferrienterobactin in E. coli) or permeases (ferripyoverdine in P. aeruginosa). Siderophores work as plant growth promoters, medicine, potential bio-control agents, and enhancers of the bioremediation of environmental pollutants. Moreover, the chemical structures of different siderophores and the membrane receptors involved in Fe uptake has opened new areas for research. But there are many questions remaining. What is the specific role of plants and microorganisms in the selectivity of metal uptake by siderophores? Why do microorganisms secrete more than one type of siderophores to meet their mineral nutritional needs? What is the relative importance of the different siderophore structures involved in environmental applications? Siderophore variability and their structural and functional characteristics in relation to microbial communities must be vigorously investigated to improve the role of siderophores in environmental applications.
