Bradyrhizobium

Bradyrhizobium is a genus of Gram-negative soil bacteria, many of which fix nitrogen. Nitrogen fixation is an important part of the nitrogen cycle. Plants cannot use atmospheric nitrogen (N₂) they must use nitrogen compounds such as nitrates.

Characteristics

Bradyrhizobium species are Gram-negative bacilli (rod shaped) with a single subpolar or polar flagellum. They are a common soil dwelling microorganism that can form symbiotic relationships with leguminous plant species where they fix nitrogen in exchange for carbohydrates from the plant. Like other rhizobia, they have the ability to fix atmospheric nitrogen into forms readily available for other organisms to use. They are slow growing in contrast to Rhizobium species, which are considered fast growing rhizobia. In a liquid media broth, it takes Bradyrhizobium species 3–5 days to create a moderate turbidity and 6–8 hours to double in population size. They tend to grow best with pentoses as a carbon source. Some strains (for example, USDA 6 and CPP) are capable of oxidizing carbon monoxide aerobically.