Higher classification Frankiaceae
Scientific name Frankia
|Similar Bacteria, High GC gram+, Casuarina, Casuarina glauca, Rhizobium|
Frankia is a genus of nitrogen-fixing, filamentous bacteria that live in symbiosis with actinorhizal plants, similar to the Rhizobia bacteria found in the root nodules of legumes in the Fabaceae family. Bacteria of this genus also form root nodules.
This genus was originally named by Jørgen Brunchorst in 1886 to honor the German biologist, A. B. Frank. Brunchorst considered the organism he had identified to be a filamentous fungus. Becking redefined the genus in 1970 as containing prokaryotic actinomycetes and created the family Frankiaceae within the Actinomycetales. He retained the original name of Frankia for the genus.
Frankia alni is the only named species in this genus, but a great many strains are specific to different plant species. The bacteria are filamentous and convert atmospheric nitrogen into ammonia via the enzyme nitrogenase, a process known as nitrogen fixation. They do this while living in root nodules on actinorhizal plants. The bacteria can supply most or all of the nitrogen requirements of the host plant. As a result, actinorhizal plants colonise and often thrive in soils that are low in plant nutrients.
Several Frankia genomes are now available which may help clarify how the symbiosis between prokaryote and plant evolved, how the environmental and geographical adaptations occurred, the metabolic diversity, and the horizontal gene flow among the symbiotic prokaryotes.