legumerhizobium

Legumerhizobium is a collective term for nitrogen-fixing bacteria that form symbiotic nodules on the roots of leguminous plants. Members of this functional group include genera such as Rhizobium, Sinorhizobium (formerly Rhizobium), Mesorhizobium, and Bradyrhizobium. These bacteria establish a mutualistic relationship with a range of legumes, from peas, beans, and lentils to clover and alfalfa, enabling biological nitrogen fixation in root nodules.

During colonization, rhizobia infect root hairs and trigger the formation of an infection thread that penetrates the root cortex. Cortical cells divide to form nodules, within which bacteria differentiate into nitrogen-fixing bacteroids. In the nodules, the plant supplies carbon and a low-oxygen environment, maintained by leghemoglobin, allowing nitrogenase to convert atmospheric nitrogen (N2) into ammonia usable by the plant and, in turn, amino acid synthesis.

Host specificity varies among legumerhizobium strains and legume species; many rhizobial strains preferentially nodulate certain hosts. In agricultural soils, nodulation depends on soil conditions, pH, moisture, and competition with native rhizobia. Inoculants containing selected strains are used to improve nodulation and yields, particularly in soils with limited compatible rhizobia or when growing high-nitrogen-demand crops.

Genetic and genomic studies highlight nod, nif, and fix gene clusters essential for nodulation and nitrogen fixation, and reveal horizontal gene transfer shaping rhizobial diversity. Legumerhizobium is central to sustainable agriculture by reducing the need for synthetic nitrogen fertilizers and enhancing soil fertility through symbiotic nitrogen fixation.