Bioprecipitation of calcium, phosphorus, and magnesium ions using ureolytic halotolerant bacteria isolated from marine environment

Mineral recovery from aqueous streams induced by bacteria has emerged as a sustainable and eco-friendly approach to improving water quality while retrieving valuable minerals. In this study, 11 out of 15 marine bacterial isolates collected from Hurghada and Ras Sedr cities were chosen based on the halotolerant-growth profile on 50 g/L NaCl. The isolate HR-106 was chosen based on the highest mineral bioprecipitation of 282 ± 0.6 mg/100 mL. This isolate produced 53.27 ± 0 µg/mL ammonia and 126.83 ± 0 mg/L non-proteinic nitrogen; in addition to that, it showed positive urease activity. This marine isolate was identified as <i>Micrococcus luteus</i>. It was exposed to increasing doses of gamma radiation and NaCl concentration (275 g/L). A confirmation of the bioprecipitated mineral profile was performed for non-irradiated and irradiated <i>Micrococcus luteus</i> using Energy Dispersive X-Ray (EDX) and X-ray Diffraction (XRD). Scanning Electron Microscope (SEM) images showed different morphologies. The Fourier Transform Infrared (FTIR) spectrum for both non-irradiated and irradiated bioprecipitate showed similar patterns that indicated that exopolysaccharides are present in both samples, acting as nucleation sites for both samples. The results demonstrated that both non-irradiated and irradiated <i>Micrococcus luteus</i> produced Ca-Mg-P bioprecepitate that showed the same chemical formula Ca_8.02Mg_9.98O₄₈P₁₂, which represents stanfieldite-like. Gamma irradiation (2kGy) stimulated mineral recovery by 40% under the tested conditions. The findings highlight the potential use of irradiated bacteria in other biotechnological applications, such as water treatment.