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

## TL;DR

A boron-tolerant Nocardia niigatensis strain was isolated from boron-rich soils and shown to have potential for bioremediation and industrial applications.

## Contribution

The study provides a comprehensive characterization of a boron-tolerant Nocardia niigatensis strain with physiological, enzymatic, and genomic insights.

## Key findings

- The strain exhibited robust growth at boron concentrations up to 50 mM, indicating potential for bioremediation.
- The strain showed positive L-glutaminase activity and a broad enzymatic profile, suggesting industrial relevance.
- Metagenomic analysis revealed differences in microbial communities linked to mineral types in boron-rich soils.

## Abstract

In this study, a Nocardia niigatensis strain was isolated from boron-rich mining soils in the Bigadiç region of Türkiye and comprehensively characterized. The primary aim of this study was to isolate boron-tolerant Nocardia species and evaluate their physiological, enzymatic, and biochemical profiles. Selective isolation techniques were employed to obtain Nocardia isolates, and species-level identification was achieved using both 16S rRNA gene sequencing and MALDI-TOF MS analysis, which consistently confirmed the isolate as N. niigatensis. In addition to molecular identification, the morphological, physiological, and biochemical characteristics of the strain were extensively investigated. The strain demonstrated notable boron tolerance, exhibiting robust growth at concentrations up to 50 mM, highlighting its potential applicability in the bioremediation of boron-contaminated environments. Physiological assays further revealed moderate halotolerance and a mesophilic growth profile, with optimal growth observed at 27–37 °C. Enzymatic screening indicated positive L-glutaminase activity, an enzyme of considerable industrial relevance. Moreover, API ZYM profiling revealed a broad enzymatic spectrum, including esterases, arylamidases, phosphatases, and glucosidases, suggesting substantial metabolic versatility. Antibiotic susceptibility testing showed sensitivity to doxycycline, tobramycin, and erythromycin, whereas resistance was observed against imipenem and several β-lactam antibiotics. Metagenomic analysis of boron-rich soils from two distinct mining sites revealed marked differences in microbial community composition, with variations in Actinobacteria abundance associated with mineral type. Overall, these findings emphasize the adaptive capacity and biotechnological potential of environmental Nocardia strains inhabiting chemically stressful ecosystems, warranting further genomic and metabolomic investigations.