This study reports, for the first time, lanthanum oxide (La₂O₃) nanoparticles (NPs) that simultaneously suppress osteosarcoma MG63 cell proliferation and promote normal Vero cell viability, a dual effect not previously documented for La₂O₃ or similar metal oxide NPs. Physico-chemical characterization revealed a unique needle-like morphology, cubic crystallinity, and dispersion stability in DMSO without acidic dispersants, properties that can influence cellular uptake, ROS modulation, and biocompatibility. Comprehensive characterization (fluorescence spectroscopy, particle size/zeta potential, Raman, XRD, TGA, ATR-FTIR, and TEM) confirmed structural stability and surface chemistry relevant to biological interactions.La₂O₃ NPs exhibited broad-spectrum antibacterial activity (Gram-positive Streptococcus pyogenes, Bacillus cereus; Gram-negative Escherichia coli, Pseudomonas aeruginosa) and strong enzymatic/non-enzymatic antioxidant capacity, supporting potential use in implant coatings and infection control. MTT assays demonstrated dose-dependent cytotoxicity in MG63 cells, with enhanced proliferation in Vero cells. In zebrafish embryos, developmental toxicity assays yielded an LC₅₀ of 2.6 mg/mL higher (less toxic) than values reported for Ag NPs (~0.3–1 mg/mL) with normal development at lower concentrations and dose-dependent malformations (e.g., impaired somite formation and skeletal deformities) at higher doses. Collectively, these findings position La₂O₃ NPs as a multifunctional platform for oncology and regenerative medicine, uniquely combining selective anticancer activity, normal cell support, antimicrobial and antioxidant functions, and a defined developmental safety margin.

Solar salt pans are extreme hypersaline environments that represent functionally specialised microbial communities mediating essential biogeochemical transformation. Vedaranyam, a coastal region of the Bay of Bengal containing artificially constructed solar salterns for salt production. There is limited information available on the metagenome diversity and functional profiling of this saltpan, which prompted us to investigate it. Here, we report the first whole metagenome sequencing to explore the dynamics of the functional structure of microbial communities in saltpan during the preharvest and postharvest phases of salt production. Methanobacteriota and Pseudomonadota dominated both phases at the phylum level, while Halobacteria comprised the most abundant class (53.2% preharvest; 48% postharvest). A notable bloom of Dactylococcopsis salina was observed during postharvest (4.28% to 12.67%) and flock doubling of Cyanobacterota relative abundance (5.5% to 10.6%), reflecting photosynthetic primary production following salt removal. Conversely, during postharvest phase sulfur oxidising Guyparkeria halophila reduced 23 fold, while the DMSP accumulating osmolyte producer Salinibaculum marinum dominated preharvest (6.98%). However, functional classification of the metagenome revealed active participation of the microbial community across five major biogeochemical cycles. Encompassing carbon fixation by cyanobacteria and diverse haloarchaea, nitrogen cycling through diazotrophy and denitrification, a cryptic preharvest sulfur cycle coupling sulfate reduction and sulphide oxidation, phase shifted DMSP catabolism, and light driven bacteriorhodopsin through archaeal energy conservation. Metagenomic assembly yielded ten metagenomic assembled genomes (MAGs), revealing the taxonomic diversity and metabolic potential of the dominant halophilic community across biogeochemical cycles. These results provide critical insights into the ecological succession from an anaerobic, chemolithotrophy-rich preharvest microbial community to an aerobic, photosynthetically driven postharvest assemblage, advancing our understanding of microbial biogeochemistry in managed hypersaline ecosystems. Graphical Abstract