Home Page Header

Welcome to the Frankia and Actinorhizal plant Website. This site provides information on the two partners in the symbiosis - actinorhizal plants and their bacterial symbionts - Frankia.

The Actinorhizal Symbiosis

Alnus incana root nodule (~2 cm; D. Benson)

Much of the new nitrogen entering temperate forests and marginal soils comes from bacteria, classified in the genus Frankia, that live symbiotically in root nodules on diverse shrubs and trees. Since Frankia belong to a group of bacteria known as actinomycetes, the nodules are termed “actinorhizal root nodules."  Collectively, the symbiosis is a major source of new nitrogen entering soil in broad areas of the world. The plants involved have become increasingly important as pioneer species as climate changes threaten to remake the global landscape over the next several decades.

The Bacterial Symbiont - Frankia

Frankia sp. strains are filamentous bacteria that convert atmospheric N2 gas into ammonia in a process known as nitrogen fixationFrankia fix nitrogen while living in root nodules on

Frankia sp. strain CcI3

“actinorhizal plants" and can supply most or all of the host plants' nitrogen needs. Consequently, actinorhizal plants colonize and often thrive in soils that are low in combined nitrogen. The availability of several Frankia genomes is helping to clarify the evolution of prokaryote/plant symbioses, environmental and geographical adaptation, metabolic diversity and horizontal gene flow among symbiotic prokaryotes.

Actinorhizal Plants

Actinorhizal plants are a diverse group of woody species found on all continents (except Antarctica). Many are common plants, like alder, bayberry, sweet fern, etc. that one might pass every day. Others live in remote parts of the world. All play significant roles in the ecology of the soils in which they grow.

Some actinorhizal plants can be used as sources of biomass for generating energy or for carbon storage; some have been used for remediating stressed or contaminated soils; others have been used for lumber, fuelwood, for preventing erosion and as coastal windbreaks. Please see the links to the various plant families for more specific information.


This website has been created by David Benson, Professor of Microbiology, Department of Molecular and Cell Biology, University of Connecticut, Storrs, CT.

The information in the site is free for use by individuals for educational or research purposes.  Under no circumstances should the images be used for commercial purposes without prior permission of the owner. Please contact the person identified as the source for permission. Support for creating this site came from the NSF-Microbial Genomes Program.

NSF_logo                  uconn-wordmark-stacked-blue

Dr. David Benson

Phone: 860-486-4258
Address: 91 North Eagleville Road
Unit 3125
Storrs, CT 06269
More: https://mcb.uconn.edu/person/david-benson/