Mesorhizobium maamorense sp. nov., a novel symbiotic nitrogen-fixing bacterium isolated from nodules of Ononis repens in the Moroccan Maâmora forest.

Mediterranean wild legumes, including Ononis repens, represent an underexplored reservoir of rhizobial diversity with ecological and agronomic significance. In this study, three novel bacterial symbionts, namely, Mesorhizobium sp. strains ORM16T, ORM5.1, and ORM12.1, were previously isolated from root nodules of O. repens in the Maâmora forest near Rabat, Morocco. Phylogenetic analysis based on 16S rRNA gene sequencing placed all three strains within the genus, Mesorhizobium, closely related to Mesorhizobium opportunistum WSM2075T. Multilocus sequence analysis (MLSA) using housekeeping genes (recA, atpD, and glnII) and whole-genome sequencing (WGS) further confirmed the distinct taxonomic position of ORM16T, with average nucleotide identity (ANI) and digital DNA-DNA hybridization (dDDH) values of 87.63% and 31.2%, respectively, both of which were below the species delimitation thresholds. Genomic analysis revealed the presence of canonical nod genes on chromosomal DNA. The type strain, ORM16T, is a gram-negative, aerobic, rod-shaped bacterium with moderate tolerance to salinity, osmotic, and thermal stress. Chemotaxonomic data highlighted the characteristic fatty acid profiles of this strain, which distinguished it from its closest relatives. Given this strain's genetic, phenotypic, and symbiotic uniqueness, we propose Mesorhizobium maamorense sp. nov., with strain ORM16T as the type strain (= DSM120599T = CCMM B1359T). Its genomic distinctiveness makes ORM16T an ideal candidate for expanding our knowledge of Mesorhizobium diversity, conducting taxonomic research, and exploring novel biotechnological applications in nitrogen fixation.