Asterionella formosa
Asterionella formosa is a species of diatom belonging to the family Fragilariaceae.
It has cosmopolitan distribution.
Taxonomy
Asterionella formosa is the type species of its genus, Asterionella.Etymology
The species name "formosa" is derived from the Latin adjective for "beautiful", or "handsome".Description
Asterionella formosa ranges from in length and 1.1–4.5 μm in width. Asterionella formosa has valves that are long and narrow, with capitate apices unequal in size. The larger apex is known as the footpole. A. formosa has a very narrow sternum and irregularly spaced striae, slightly offset from one another at the sternum. Some A. formosa have irregularly spaced marginal spines between striae. At each end, there is a porefield. Rimoportulas have been observed to occur at either or both ends of the valve.Within each cell is a nucleus at their center and 6–8 golden-brown chromatophores.
Asterionella formosa colonies consist of cells joined at their valve faces' footpoles by mucilage pads. Their colonies consist of 8–20 cells and take on a spiral, star-like shape. They may also occur in a closed ring shape, but this is rare.
Habitat and distribution
Asterionella formosa is common in mesotrophic and eutrophic lakes and slow-moving river plankton around the world, and is especially common in the northern hemisphere. It has become increasingly common in oligotrophic mountainous lakes.Ecology
Asterionella formosa colonies may be colonized by small, sessile choanoflagellates, or infested by Zygorhizidium planktonicum, a parasitic chytrid fungus. To prevent the fungus from spreading, affected cells in the colony usually induce cell death.A. formosa laboratory models have been observed to have dynamic microbiomes with many bacterial species, mostly from the phyla Proteobacteria and Bacteroidetes. Most of the bacteria were heterotrophic and more than half could metabolize glycolate.