Nostoc azollae
Classification
Domain: Bacteria
Phylum: Cyanobacteria
Class: Cyanophyceae
Order: Nostocales
Family: Nostocaceae
Genus: Nostoc
Species
NCBI: Taxonomy |
Nostoc azollae
Description and Significance
Nostoc azollae, from the genus "Nostoc", is a cyanobacteria (1), meaning it is a phototrophic organism that creates its own energy through photosynthesis. The microbe grows as unbranched filaments and differentiates itself into three seperate types of cells. Heterocysts, which differentiate in response to nitrogen deficiencies, and act as sites of fixation for the environment. These make up anywhere from 3-10% of the microbe's cells. N. azollae is also capable of creating two other kinds of cells, hormongia, consisting of short filaments, and spore-like akinetes to make up for any limitations in the environment (2).
The significance of the microbe is found within its symbiosis with Azolla filiculoides, a type of plant native to warm tropical regions all across the globe (3). The fern possesses numerous small cavities all along its surface that house N. azollae and allow for the transfer of nutrients between the two symbionts (4).
Genome Structure
Sequence and Size:
Only a few strains of N. Azollae have been sequences, chiefly Nostoc Azollae 708 (Figure 1), which had a genome size of 5.84 megabytes (8). N. Azollae possessed a small G+C content of only 38.3%, and carried with it 4 rRNA clusters alongside 44 tRNA species, making up the full set of amino acids. Notable within the gene is that intact genes, as opposed to pseudogenes, compose 52% of the genome, which is the lowest of any cyanobacteria sequenced thus far, owing partly to the massive amount of pseudogenes that comprise the rest of the genome. In addition, N. Azollae has the some of the lowest intact CDS counts of any similar cyanobacteria sequenced (9).
Interesting Features:
The genome contains 2 plasmids, and is approximately made up of 31.2% Pseudogenes, most likely due to its nature as an integral symbiont. N. Azollae is considered an obligate, usually surviving in the highly sheltered environment provided by its host. The current information from the sequences suggests that the genome is degrading even today (9). Among the psuedogenes is the DNA replication initiator, implying N. Azolla has difficulties in reproduction. The current genome suggests that the role of N. Azollae as a nitrogen fixation microbe has been made obligatory, which benefits its host most of all. Although N. Azollae can live beyond their host, it comes at great difficulty and stops their growth(9).
Cell Structure, Metabolism and Life Cycle
Cell Structure:
N. Azollae typically grow as filamentous, extracellular heterocysts. These cells are excellent sources of nitrogen fixation within their cell, and it is estimated that these sites fix more than three times the amount of nitrogen than a legume-rhizobium symbiosis.
Ecology and Pathogenesis
N. azollae, like most of the Nostoc genus, inhabits freshwater, tropical, temperate, and polar terrestrial systems, but are rarely found in marine environments (2).
Habitat; symbiosis; biogeochemical significance; contributions to environment.
If relevant, how does this organism cause disease? Human, animal, plant hosts? Virulence factors, as well as patient symptoms.
References
1. https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0011486
2. https://www.uniprot.org/proteomes/UP000001511
3. https://www.nobanis.org/globalassets/speciesinfo/a/azolla-filiculoides/azolla_filiculoides.pdf
4. https://sites.duke.edu/pryerlab/files/2019/02/Ariana_Azolla%E2%80%93Nostoc_2019.pdf
6. https://digitalcommons.wku.edu/cgi/viewcontent.cgi?article=1467&context=stu_hon_theses
7. https://www.sciencedirect.com/topics/agricultural-and-biological-sciences/nostoc
8. Handbook of Cyanobacteria
9. https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0011486
Author
Page authored by John Weglarz, student of Prof. Jay Lennon at IndianaUniversity.