Frankia alni

A Microbial Biorealm page on the genus Frankia alni

Frankia sp. From Genoscope.

Classification

Higher order taxa

    Bacteria; Actinobacteria; Actinobacteria (class); Actinobacteridae; Actinomycetales; Frankineae; Frankiaceae; Frankia

Species

NCBI: Taxonomy

Frankia alni

Description and significance

"The actinomycete Frankia is of fundamental and ecological interests for several reasons including its wide distribution, its ability to fix nitrogen, differentiate into sporangium and vesicles (specialized cell for nitrogen-fixation), and to nodulate plants from about 24 genera." [1]

Species of the Frankia Genus are Gram positive bacteria.Frankia sp. are filamentous nitrogen-fixing bacterium that grow by branching and tip extension and thus resemble the antibiotic-producing Streptomyces sp. . They live in the soil and have a symbiotic relationship with certain woody angiosperms, called actinorhizal plants. During growth, the Frankia sp. produce three cell types: sporangiospores, hyphae, and diazo-vesicles (spherical, thick walled, lipid-enveloped cellular structures). The diazo-vesicles are responsible for the supplying of sufficient Nitrogen to the host plant during symbiosis. Frankia supplies most or all of the host plant nitrogen needs without added nitrogen and thus can establish a nitrogen-fixing symbiosis with host plants where nitrogen is the limiting factor in the growth of the host. Therefore, actinorhizal plants colonize and often prosper in soils that are low in combined nitrogen. Symbiosis of this kind adds a large proportion of new nitrogen to several ecosystems such as temperate forests, dry chaparral, sand dunes, mine wastes, & etc[3].

The Frankia alni ACN14a was first isolated in Tadoussac, Canada from a green alder (Alnus crispa). Except for Australia and Antarctica, Frankia alni can be isolated from soils on all continents. Frankia alni causes root hair deformation in a way that it enters the cortical cells and induces the nodule formations, which look like those induced by Rhizobium in legumes. Then, the nodules are colonized by vegetative hyphae (mycelium filaments) that differentiate into diazo-vesicles. Reductive nitrogen fixation takes place in the diazo-vesicles and this process is protected from molecular oxygen by many layers of tightly stacked hopanoid lipids.

Genome structure

The genome sequencing project of Frankia alni ACN14a was done at the Genoscope sequencing center and was completed on 03/08/2006. The genome of Frankia alni ACN14a contains a circular chromosome that is 7,497,934 necleotides long. It also cantains plasmids, but the amount was not clear based on my research. It has a high G-C content of 72.8% and contains 88% coding regions. The genome has 6,786 genes, comprising of 6,711 protein coding genes, 63 structural RNAs, and 12 pseudo genes.[3]

Cell Structure and Metabolism

Hopanoids role in cell membranes. From Eberhard Karls University Tubingen.

Frankia vesicle. From Las Pilitas Nursery.

Three different structural forms characterize Frankia: hyphae, sporangia, and vesicles. In free-living Frankia cells, the hyphae are septate and tightly interwoven in culture and produce terminal or intercalary multilocular sporangia. Vesicles are normally initiated when the nitrogen source in the medium is withdrawn or when growth occurs on amino acids or other nitrogen sources that cannot be degraded to ammonia.[2]

Frankia alni under goes Glycerolipid metabolism, which includes Glycolysis, and fatty acid metabolism. In symbiosis, when provided with NADH, succinate, phosphorylated hexoses plus pyridine nucleotides in various combinations, trehalose and other sugars, or a combination of malate, glutamate, and NAD+, vesicle cluster suspensions from Alnus species respire. Frankia alni also under goes nitrogen metabolism through the vesicles that are the main site of nitrogenase proteins. Vesicle appearance correlates with nitrogenase activity and degeneration of vesicles and nodules coincides with loss of nitrogenase activity. Optimal nitrogenase activity occurs at 20 kPa of O2, and is inhibited at any kPa O2 of above 25, therefore, a variety of mechanisms are used to limit the O2 diffusion to nitrogenase in symbiosis.[2]

Ecology

Describe any interactions with other organisms (included eukaryotes), contributions to the environment, effect on environment, etc.

Pathology

Studies have not been able to identify Frankia as a pathogen, causing any disease.

Application to Biotechnology

Does this organism produce any useful compounds or enzymes? What are they and how are they used?

Current Research

Enter summaries of the most recent research here--at least three required

References

[1] Lavire, C., Cournoyer, B. "Progress on the Genetics of the N2-fixing actnorhizal symbiont Frankia ". Plant and Sil. July 2003, Volume 254, Number 1. p.125-137. [1]

[2] Benson, D., Silvester, W., "Biology of Frankia Strains, Actinomycete Symbionts of Actinorhizal Plants". Microbiological Reviews, June 1993. p.293-319 [2]

[3] Genoscope: Frankia alni: A symbiotic nitrogen-fixing actinobacterium

[4] Tjepkema,J. D., Ormerod, W. O.,Torrey, J. G.," Vesicle Formation and acetylene reduction (nitrogenase activity) in Frankia sp. CpI1 in Culture". Microbiological Reviews. 1980, Volume 27. p.815-823.

[5] Zhang, X.,Benson, D. R., "Utilization of Amino Acids by Frankia sp. strain CpI1". Arch. Microbiol. 1992, Volume 158. p256-261.

Edited by Mandana Farahani student of Rachel Larsen and Kit Pogliano at UCSD.