Siderophores are small organic molecules produced by microorganisms under iron-limiting conditions which enhance the uptake of iron to the microorganisms. In environment, the ferric form of iron is insoluble and inaccessible at physiological pH (7.35-7.40). Under this condition, microorganisms synthesize siderophores which have high affinity for ferric iron. These ferric iron-siderophore complexes are then transported to cytosol. In cytosol, the ferric iron gets reduced into ferrous iron and becomes accessible to microorganism. In recent times, siderophores have drawn much attention due to its potential roles in different fields. Siderophores have application in microbial ecology to enhance the growth of several unculturable microorganisms and can alter the microbial communities. In the field of agriculture, different types of siderophores promote the growth of several plant species and increase their yield by enhancing the Fe uptake to plants. Siderophores acts as a potential biocontrol agent against harmful phyto-pathogens and holds the ability to substitute hazardous pesticides. Heavy-metal-contaminated samples can be detoxified by applying siderophores, which explicate its role in bioremediation. Siderophores can detect the iron content in different environments, exhibiting its role as a biosensor. In the medical field, siderophore uses the "Trojan horse strategy" to form complexes with antibiotics and helps in the selective delivery of antibiotics to the antibiotic-resistant bacteria. Certain iron overload diseases for example sickle cell anemia can be treated with the help of siderophores. Other medical applications of siderophores include antimalarial activity, removal of transuranic elements from the body, and anticancer activity. The aim of this review is to discuss the important roles and applications of siderophores in different sectors including ecology, agriculture, bioremediation, biosensor, and medicine.

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These experiments were performed to characterize the relationship between lipid peroxidation and hepatocyte viability in iron overload. Hepatocytes were isolated from rats with chronic dietary iron overload and the effects of in vitro iron chelation on lipid peroxidation, cell viability and ultrastructure were studied over a 4-hr incubation period. Cell viability was significantly reduced at 3 and 4 hr in iron-loaded hepatocytes compared with controls and was preceded by an increase in iron-dependent lipid peroxidation. Similarly, extensive degenerative ultrastructural changes were observed in iron-loaded hepatocytes compared with controls after 4 hr of incubation. In vitro iron chelation with either deferoxamine or apotransferrin protected against lipid peroxidation, loss of viability and ultrastructural damage in iron-loaded hepatocytes. The addition of an antioxidant, alpha-tocopherol, also protected against lipid peroxidation and preserved cell viability over a 4-hr incubation. The protective effects of iron chelators and alpha-tocopherol support a strong association between iron-dependent lipid peroxidation and hepatocellular injury in iron overload.

Biofilm is the assemblage of microbial cells that are irreversibly associated with biotic and abiotic surfaces and is usually enclosed in the self secreted extracellular polymeric substances (EPS). The presence of EPS in biofilm makes the microbial population resistance against antibiotics and other drugs. Biofilms are considered as a serious challenge to pharmaceutical industries because most of the microbial diseases are now associated with biofilm. In this context, we have addressed the biofilm potentialities of Pseudomonas aeruginosa, which has been found to be associated with several deadly diseases including septicemia, urinary tract infections, and gastrointestinal infections, and wherein biofilm plays a crucial role in pathogenesis. Since silver had been used globally for a long time for treating a wide range of illnesses from burn wounds, typhoid, and anthrax to bacterial conjunctivitis in newborns, but its antibiofilm activity is still unknown. Thus, in this current study, we have tried to examine the antibiofilm potentiality of silver against the biofilm of Pseudomonas aeruginosa. Our result showed that silver exhibited considerable antimicrobial property against Pseudomonas aeruginosa where the minimum inhibitory concentration (MIC) was found at 25 µg/ml. Biofilm inhibition by silver against Pseudomonas aeruginosa was then evaluated by crystal violet (CV) staining, estimation of total biofilm protein and microscopy based microbial adherence test using the sub MIC doses of silver. The results showed that all the tested sub MIC doses of silver exhibited considerable antibiofilm activity against P. aeruginosa, wherein the maximum biofilm attenuation was showed by a silver concentration of 20 µg/ml. We also observed that all these sub MIC doses of silver neither interfere with the growth cycle of the bacteria nor affect the cell viability but only attenuates biofilm formation property of the bacteria. The current study deciphers a new axis in biofilm biology where a metal like silver can inhibit the * Corresponding author. B. K. Sharma et al. 678formation of biofilm markedly. Thus, the knowledge gathered in this study may help the pharmaceutical sector to design combinatorial drug where silver could be an important partner to reduce the load of pathogenesity caused by biofilm.

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