Characterization of a Boron-Tolerant Nocardia niigatensis Isolated from Boron- Rich Soils: Physiological, Enzymatic, and Genomic Insights

In this study, a Nocardia niigatensis strain was isolated from boron-rich mining soils in the Simav region of Turkey and comprehensively characterized in terms of its physiological, enzymatic, and molecular properties. Isolation was performed using selective media, and strain identification was achieved through 16S rRNA gene sequencing and MALDI-TOF MS analysis, both of which consistently identified the isolate as Nocardia niigatensis . The strain exhibited significant boron tolerance, with robust growth observed at concentrations up to 50 mM, indicating its potential for bioremediation in boron-contaminated environments. Salt and temperature tolerance tests showed moderate halotolerance and a mesophilic growth profile. Enzymatic screening revealed positive activity for L-glutaminase, which is of industrial relevance. Additionally, API ZYM analysis indicated a broad enzymatic repertoire including esterases, arylamidases, phosphatases, and glucosidases. Antibiotic susceptibility testing demonstrated sensitivity to doxycycline, tobramycin, and erythromycin, while resistance was observed against imipenem and several beta-lactam antibiotics. Metagenomic analysis of the boron-rich soils revealed distinct microbial community structures between two mining sites, with Actinobacteria dominance varying according to mineral type. This highlights the ecological influence of mineral composition on microbial diversity. Overall, the findings underscore the adaptive capacity and biotechnological potential of environmental Nocardia strains, particularly in stress-rich ecosystems such as boron mines. Further genomic and metabolomic analyses are warranted to explore the full application potential of this isolate in environmental and industrial microbiology.