Abstract <p>The current study investigated 17 bacterial strains for their ability to synthesize gold nanoparticles (AuNPs) from the aryldiazonium gold(III) salt (DS-AuCl₄). The study aims to investigate the ability of bacterial cell biomass in the stationary phase of growth to synthesize AuNPs at 28 °C and 37 °C. Eleven bacterial strains were isolated from soil and identified using the VITEK® 2 system and 16S rRNA sequencing. An additional six strains were obtained from the American Type Culture Collection (ATCC). The investigated Gram-positive and Gram-negative bacterial strains successfully produced anisotropic AuNPs at a cell density of 2.0 McFarland (6.0 × 10⁸ CFU/mL). Nanoparticle formation was faster when samples were incubated at 37 °C than at 28 °C across all bacterial strains. The results of UV-vis spectroscopy confirmed the presence of AuNPs, with peaks observed centered at 550 nm. High-resolution transmission electron microscopy (HR-TEM) revealed a variety of morphologies, including spheres, rods, triangles, pentagons, hexagons, irregular shapes, and flower-like structures. Gram-positive and Gram-negative bacteria synthesized AuNPs of sizes 38.7 ± 26.0 and 34.0 ± 18.6 nm, respectively. Lattice-spacing analysis confirmed the formation of metallic AuNPs. Energy-dispersed X-ray spectroscopy (EDS) validated the presence of gold in the samples, and X-ray photoelectron spectroscopy (XPS) confirmed the elemental composition of AuNPs at 84.0 eV. These nanoparticles have potential applications in cancer therapy and diagnosis, antibacterial treatments, and drug delivery.</p> Key points <p>• <i>The AuNPs were synthesized using various bacterial strains</i></p> <p>• <i>The gold precursor is aryldiazonium gold(III) salt</i></p> <p>• <i>Various anisotropic morphologies were obtained</i></p> Graphical abstract <p>Created in BioRender. Ahmady, I. (2025)</p> <p></p>