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Antibacterial activity of siderophores from marine actinobacteria against Gram negative bacterial pathogens

Aim: To study the siderophore production and antibacterial activity of actinobacteria isolated from mangrove plants and sediments. Methodology: In the present study, 112 actinobacterial strains were recovered from mangrove rhizosphere sediments and plants collected from Andaman Islands and mangrove zones at Vellar estuary, Parangipettai, South India. All the strains were screened for antibacterial activity against Escherichia coli, Aeromonas hydrophila, Providencia stuartii, Salmonella paratyphi and Klebsiella pneumoniae and also studied for siderophore production. Results: In total, 13 actinobacterial strains showed broad spectrum of activity against all the five Gram negative bacterial pathogens tested with zone of inhibition ranging between 9.2 to 18.7 mm. In CAS assay,14 actinobacterial strains were found to produce siderophore. Among them, strain MEA 11 was found to produce 88% siderophore in iron free succinate broth. Results of CAS plate assay and FeCl3 test revealed that the siderophore produced by the strain MEA11 as hydroxamate type. In optimization study, variables such as glucose (17.7±0.9 and 17.7±0.3), malt extract (14.7±0.9 and 15.0±0.6) and MgSO4 (12.0±0.6 and 12.3±0.3) were found to influence siderophore production and antimicrobial activity. Further, this multi potentialstrain MEA 11 was characterized and identified as Streptomyces tendae. Interpretation: These results revealed that the marine ecosystem of Andaman coastal area and Parangipettai region harbored a rich consortium of many bioactive actinobacteria, which could synthesize novel bioactive compounds of pharmacological significance.