Elmer L. Eide

Document Type

Thesis - Open Access

Award Date


Degree Name

Master of Science (MS)

Department / School

Biology and Microbiology

First Advisor

Robert M. Pengra


Biological nitrogen fixation, a means of alleviating our increasing dependence on synthesized nitrogen fertilizers, is being studied with renewed interest. Production of nitrogen fertilizer requires large amounts of natural gas and other non-renewable energy sources, while the energy for biological nitrogen fixation is derived either directly or indirectly from photosynthesis. With only limited supplies of natural gas and an increasing population, and thus increasing demand for food, the advantages and even necessity of understanding and enhancing biological nitrogen is obvious. The nitrogenase enzyme complex which catalyzes the reduction of dinitrogen to ammonia is possessed by a limited number of species of procaryotic organisms. The nitrogen fixing procaryotes are categorized as non-symbiotic (free living) nitrogen fixers and symbiotic nitrogen fixers. Nitrogen fixation by the leguminous plant-rhizobium bacteria symbiosis is important because a portion of the fixed nitrogen accumulated is harvested as high protein foods or plant forage while the remaining fixed nitrogen eventually enters the soil. Studies on the rhizobia from cultivated legumes have been extensive and economically rewarding. However, rhizobia from thousands of other legumes including rhizobia symbiosing with legumes native to South Dakota have been inadequately studied. As a result, information on the symbiotic nitrogen fixing capabilities and characteristics of rhizobia from most leguminous species varies from substantial to nonexistent. This study was initiated with the purpose of isolating and characterizing the rhizobia from Astragalus flexuosus (flexile milk vetch) and Glycyrrhiza lepidota (American licorice). For comparison, strains of Rhizobium trifolii, which symbiose with Trifolium spp. (true clovers) and have been extensively studied, were isolated from Trifolium spp. and characterized.

Library of Congress Subject Headings

Nitrifying bacteria,




South Dakota State University

Included in

Microbiology Commons