BIOSYNTHESIS AND BIOACTIVITY OF NIOBIUM OXIDE NANOSTRUCTURES USING LACTIC ACID BACTERIA SUPERNATANTS

Niobium (Nb) is a metal with attractive physicochemical properties, low cytotoxicity, and potential for diverse biomedical applications. To fully exploit its nanotechnological potential, it is essential to adopt sustainable and environmentally friendly synthesis methods. In this context, green synthesis has emerged as a promising approach for producing nanostructures, reducing environmental impact by eliminating toxic reagents and lowering costs. Among the resources considered for green synthesis of nanoparticles are lactic acid bacteria (LAB), microorganisms widely used in industry due to their ability to produce compounds with diverse and valuable biological activities. In this study, niobium-based nanostructures were green-synthesized using cell-free supernatants obtained from cultures of Lactobacillus rhamnosus (Nb-Lcr-CFS) and Lactobacillus paracasei UFTM 2.9 (Nb-Lp-CFS), which served simultaneously as reducing and stabilizing agents. The resulting materials were characterized in terms of composition, morphology, crystallinity, and surface charge. In vitro assays employing Vero-CCL81 cells were conducted to assess cytotoxicity, while antibacterial and antibiofilm activities were evaluated against Escherichia coli ATCC 25922. Ultraviolet-Visible (UV/Vis) and Fourier-Transform Infrared (FTIR) spectroscopy indicated the formation of niobium-based nanostructures, specifically hydrated niobium oxide (Nb₂O₅·nH₂O), containing specific organic groups that may be associated with biomolecules present in the supernatants. X-Ray Diffraction (XRD) analysis revealed low crystallinity, consistent with the amorphous or semicrystalline nature commonly observed in hydrated niobium oxides. Scanning Electron Microscopy (SEM) and Scanning-Transmission Electron Microscopy (STEM) micrographs demonstrated that the materials consisted of agglomerates of nanoscale particles, with estimated diameters of approximately 90 nm for Nb-Lp-CFS and 255 nm for Nb-Lcr-CFS. Zeta potential measurements indicated that the structures possess an anionic character, which was more pronounced for Nb-Lcr-CFS, suggesting greater colloidal stability. Cell viability assays indicated that the synthesized nanostructures exhibited cytotoxic effects only at high concentrations. In addition, the materials demonstrated both antibacterial and bactericidal properties against E. coli, as well as a marked ability to inhibit bacterial biofilm formation, underscoring their potential for future biomedical and antimicrobial applications.

This work was supported by Fundação de Amparo à Pesquisa do Estado de Minas Gerais (FAPEMIG - APQ-00458-24) and Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq - Grant 405457/2023-5).