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United States Department of Agriculture

Agricultural Research Service

USDA ARS National RHIZOBIUM Database
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Our mission is to support application of low-input sustainable agriculture by:

1. Providing, to the best of our ability, technical information about rhizobia, their preservation, and cultural and symbiotic characteristics.
2. Acquiring and preserving the nitrogen-fixing bacterial symbionts of leguminous plants with the goal of maintaining widest possible genetic diversity.
3. Maintaining quality control of new and existing germplasm by evaluation of microbiological purity and by examination of nodulation of the original trap host plant.
4. Distributing cultures to the public and private sectors without charge for these services.
5. Developing or adapting techniques in molecular biology for the determination of genetic diversity of rhizobia, to investigate interactions with their host plants and to identify novel characteristics.
6. Acquiring, maintaining, evaluating quality, and distributing type strains for all the different taxa of nitrogen-fixing legume symbionts.
7. Participating in the UNESCO program.

Although navigation through this site is still possible from this page, access to the
USDA ARS National RHIZOBIUM Database is via another server.

Questions concerning database content can be directed to
Patrick Elia.

However, questions concerning technical details about the database should be addressed to GRIN.



Electron micrograph of bradyhriobial cells grown in culture solution

1. Isolation, preservation and ultimately characterization of soybean bradyrhizobia from soil samples collected in Vietnam.
2. Isolation, preservation and ultimately characterization of rhizobia for native American clover species from soil samples collected predominantly in California.
3. Characterization of rhizobia for symbiotic traits, specifically those originating from soybean, alfalfa and clover isolated from plants grown in imported soil samples.
4. Development of techniques in molecular biology for application to the genetic characterization of microorganisms that interact with eukaryotic organisms.
5. Currently the focus is two-fold: i) evaluation of lateral gene transfer and its affect on the determination of evolutionary biology of rhizobia and related bacterial genera and ii) determination of chromosome plasticity in Rhizobium meliloti, the symbiont of alfalfa.
6. Evaluation of protocols that have been developed as methods for the investigation of other plant-microbe interactions.


Early History

The Agricultural Research Service (ARS) of the U. S. Department of Agriculture (USDA) has maintained a collection of nitrogen-fixing bacterial legume symbionts for most of the last century. Some of the initial isolates (cultures accessed in 1913) originated from the Arlington Farm in Northern Virginia, which is now the site of the Pentagon. The ARS did not directly fund the activities of the collection. The collection of strains grew, especially in the 1930s and 1940s, in response to the requirements of research programs in the USA. During this time and throughout the 1950s and 1960s the scientists at USDA produced inoculants for small scale research programs at universities as well as those of other government establishments. At this time the collection had already earned an international reputation. 

National Recognition

During the 1970s, an awareness of the critical importance of biological nitrogen fixation in agricultural production ensued because of the energy crisis brought about by the oil embargo. It was quite evident that the limitation of nitrogen in agriculture was a world-wide phenomenon and that poor nations suffered the most because of the rising energy cost. The result was that it became increasingly necessary to rely on the production of leguminous crops and the management of the nitrogen-fixing symbiosis to provide mankind with food, raw materials, and alternative energy sources. Within this climate, the need for a culture collection of characterized legume microbial symbionts was identified during the first three North American Rhizobium conferences. The USDA at Beltsville was unanimously recognized as possessing the most comprehensive collection of strains, and the established links with the public and private sectors were considered advantageous for technology transfer.

International Recognition

Because the goals of the culture collection were relevant at the international level, funding for activities was at first provided by the Agency for International Development (USAID). This support was responsible for the establishment of the basic infrastructure in the laboratory to preserve and record characteristics of the accessions of the collection. One of the objectives of USAID's funding was to provide a means by which scientists of developing nations could preserve their cultures and guard against their loss. The International status of the collection was further advanced during the 1980s by its designation as a Microbiological Resource Center (MIRCEN) by the United Nations Educational and Cultural Organization and the United Nations Environmental Program (UNESCO/UNEP).

ARS funding

ARS, in recognition of the importance of the collection, initiated funding when USAID support ended in 1990. Although funding from USAID for international activities ceased, the collection continues to honor its international obligations in the UNESCO program, and the activities associated with the objectives of the MIRCENs remain active. The collection also became the repository for the type strains of the genera and species of the legume nitrogen-fixing microbial symbionts in 1993.

 Name Title  Phone
  Patrick Elia  Microbiologist

 (301) 504-5029

For information you may also contact Patrick Elia  

UNESCO Affiliation

Although usually unrecognized, microorganisms are highly important genetic resources. These resources have extensive potential. Culture collections of microorganisms (genetic resource centers) are indispensable for the preservation and maintenance of valuable strains and mutants. A genetic resource center is an essential investment to guard against loss the massive investments made in long-term basic and applied microbiological research. The role of microbial genetic resource centers is essential because it is extremely difficult to reisolate from nature an exact replica of a particularly useful strain in the event of loss. Such a loss in most cases is final because retrieval from nature of a replica may only be possible at prohibitive cost. Besides an investment against loss of important resources, microbial genetic resource centers very often also are the origin of important research programs, supplying information and basic data in addition to the genetic resources.

After the United Nations Conference on Human Environment, held in Stockholm in 1972, the United Nations Environment Program (UNEP), the United Nations Educational, Scientific and Cultural Organization (UNESCO) and the International Scientific Community launched a world-wide program for preserving microbial gene pools and making them accessible to developing countries. In 1974, the concept of the Microbiological Resource Center (MIRCEN) was formulated. In 1975, an action plan was developed to establish a world-wide network of MIRCENs with the following objectives:

  • To provide the infrastructure for building a world network which would incorporate regional and interregional cooperating laboratories geared to the management, distribution, and utilization of the microbial gene pool.
  • To strengthen efforts relating to the conservation of the microorganisms with emphasis on Rhizobiumgene pools in developing countries with an agrarian base.
  • To foster the development of new expensive technologies that are native to the region.
  • To promote the application of microbiology in the strengthening of rural economies.
  • To serve as focal centers for the training of manpower and the imparting of microbiological knowledge.

One of the avenues pursued to reach these goals is the funding of short-term fellowships for training at one of the MIRCENs. Currently, the MIRCEN at Beltsville hosts trainees with UNESCO support as visiting scientists in the laboratory. Visitors receive hands on training in the microbiology of Rhizobium, usually by doing short-term research projects using approaches of molecular biology. However, training in more applied methods with relevance to the management of biological nitrogen fixation for efficient crop production are also available.

Requests And Deposits
Two visiting scientists examining the characteristics of a rhizobial culture growing on a solid surface nutrient medium contained in a petri plate

Most journals now require authors to submit newly isolated microbial cultures to recognized culture collections for preservation as part of the process of peer reviewed publication. The USDA ARS National Rhizobium Germplasm Collection is a recognized collection and will accept cultures that originated from plant root nodules. Also, we encourage authors, who have proposed new species, to consider our collection as a recipient. Unlike most collections, we also preserve other cultures in addition to type strains. Therefore, we are able to maintain strains representing the diversity within species. Since we distribute cultures free of charge, our collection is a very cost-effective way in which future authors can include a comprehensive set of strains in their studies.

We strongly encourage communication by e-mail ( When requesting or depositing strains please provide us with the following:


  1. A copy of the scientific paper, if characterizations have been published.
  2. Original host of isolation.
  3. Location of nodule collection or origin of soil sample.
  4. Name and address of person depositing culture.
  5. Culture identification number used in the literature.
  6. A statement indicating permission to distribute culture(s).
  7. and of course the cultures.

We would encourage that for diversity or taxonomy studies that in addition to the type or reference strains all other characterized isolates be sent to us.


  1. If at all possible the USDA accession number.
  2. Host plant of origin.
  3. Name and full mailing address.
  4. Telephone number.
  5. Whether you would like instructions and media formulation.

In some cases we have noticed that cultures sent abroad by regular mail fail to arrive. This has been especially the case with countries in Latin America and the Caribbean. It would be helpful, if you think there might be an importation issue in your country, to provide us with any required labels for passage through customs.

Bradyrhizobium Microarray Initiative team is dedicated towards sharing and dissemination of public information on all aspects of Bradyrhizobium genomics.  The website is meant to serve research, communication and educational needs as they relate to Bradyrhizobium genomics. 

Last Modified: 2/28/2013