Siderophores are low-molecular-weight and high-affinity molecules produced by bacteria under iron-limited conditions. Due to the low iron (III) (Fe⁺³) levels in surface waters in the marine environment, microbes produce a variety of siderophores. In the current study, halophilic bacteria Bacillus taeanensis SMI_1, Enterobacter sp., AABM_9, and Pseudomonas mendocina AMPPS_5 were isolated from marine surface water of Kalinga beach, Bay of Bengal (Visakhapatnam, Andhra Pradesh, India) and were investigated for siderophore production using the Chrome Azurol S (CAS) assay. The effect of various production parameters was also studied. The optimum production of siderophores for SMI_1 was 93.57% siderophore units (SU) (after 48 h of incubation at 30 °C, pH 8, sucrose as carbon source, sodium nitrate as nitrogen source, 0.4% succinic acid), and for AABM_9, it was 87.18 %SU (after 36 h of incubation period at 30 °C, pH 8, in the presence of sucrose, ammonium sulfate, 0.4% succinic acid). The maximum production of siderophores for AMPPS_5 was 91.17 %SU (after 36 h of incubation at 35 °C, pH 8.5, glucose, ammonium sulfate, 0.4% citric acid). The bacterial isolates SMI_1, AABM_9, and AMPPS_5 showed siderophore production at low Fe⁺³ concentrations of 0.10 µM, 0.01 µM, and 0.01 µM, respectively. The SMI_1 (73.09 %SU) and AMPPS_5 (68.26 %SU) isolates showed siderophore production in the presence of Zn⁺² (10 µM), whereas AABM_9 (50.4 %SU) exhibited siderophore production in the presence of Cu⁺² (10 µM). Additionally, these bacterial isolates showed better heavy-metal chelation ability and rapid development in seed germination experiments. Based on these results, the isolates of marine-derived bacteria effectively produced the maximum amount of siderophores, which could be employed in a variety of industrial and environmental applications.

This study explores the green synthesis of silver nanoparticles (AgNPs) using Cymbopogon citratus (lemongrass) extract as a reducing agent. Synthesis was confirmed by a color change (light yellow to dark brown) under optimal conditions: 1.50 mM silver nitrate, 3.5% v/v extract, at 100 °C, with a pH of 9, and for 60 min. The AgNPs exhibited spherical morphology, a hydrodynamic diameter of 135.41 ± 49.30 nm, a zeta potential of −29.9 ± 1.4 mV, crystalline structure, and minimal aggregation. AgNPs showed significant antibacterial activity, particularly at >20 µg/well, with the zones of inhibition varying by bacterial strain. In vitro studies demonstrated anti-inflammatory, antidiabetic (α-glucosidase and α-amylase inhibition), and antioxidant activities, with AgNPs outperforming plant extract and nearing standard efficacy at higher concentrations. Cyto-toxicity studies indicated that AgNPs and plant extract were less toxic than doxorubicin but exhibited concentration-dependent effects on cancerous and non-cancerous cells. Eco-toxicity assays revealed that AgNPs were less acutely toxic than controls but posed risks with prolonged exposure. This work highlights the eco-friendly synthesis of AgNPs and their potential in biomedical applications, demonstrating efficacy in antibacterial and antioxidant activities.