Rhizobacteria are root-colonizing bacteria that form a symbiotic relationship with many legumes. Though parasitic varieties of rhizobacteria exist, the term usually refers to bacteria that form a relationship beneficial for both parties (mutualism). Such bacteria are often referred to as plant growth promoting rhizobacteria, or PGPRs. Though microbial inoculants are indisputably beneficial for crops, they are not widely used in industrial agriculture, as large-scale application techniques have yet to become economically viable. A notable exception is the use of rhizobial inoculants for legumes, such as peas. Inoculation with PGPRs ensure efficient nitrogen fixation, and they have been employed in North American agriculture for over 100 years.