Pseudo-nitzschia australis is a diatom that thrives in the ocean. A diatom has two distinct valves, separated by a wall of silicon dioxide. These diatoms are responsible for quite a bit of the oxygen in the atmosphere. The cell itself is long and needle-like, with a volume of about 2,415 µm3. It is also a phytoplankton, or a photoautotroph, which is an organism that has chloroplasts and uses sunlight and carbon dioxide as sources of energy. Even under ideal conditions phytoplankton will only live for 1 to 2 days. It is known that P. australis has a form of motility, but as of right now, the mechanism is unknown.
The reproductive cycle of P. australis can be achieved in two different ways. In the first case, the two separate valves each make a daughter cell, which will stay attached to the parent valve. The original median will split to make the outer cell walls, and new ones will be made between the parent cells and the daughter cells. Often, the splitting of the original wall will not fully occur, and lines of colonies will arise. However, this form of reproduction will result in a decrease in cell size. To overcome this, there is another form of reproduction. In this case, two P. australis will come together. They will both produce gametes. These gametes will join, and become new cells.
Since P. australis needs light to survive, it lives near the surface of the water. It still needs other nutrients though, such as iron. When the water is colder, there will be an upwelling of the water from closer to the ocean floor, which will bring the needed iron with it. This will cause the phytoplankton population to increase. This is referred to as a “bloom”. In warmer water though, this upwelling does not occur, causing the organisms to die out.P. australis, along with the other species of the genus Pseudo-nitzschia, will sometimes produce domoic acid. This is a tricarboylic acid that acts as a secondary metabolite. It is produced the most during the end of exponential growth and the beginning of the stationary phase. However, it is not always produced. There is much speculation as to its real purpose. Many say that it is made when iron is scarce, while others say the exact opposite of this.
Phytoplankton, including P. australis, is used as a basic source of food for many marine animals. These animals include scallops, crabs, clams, anchovies, and even whales. Others will then eat these animals, and so on up the food chain. Unfortunately, domoic acid can negatively affect some of animals, including birds, sea lions and humans. It will irreversibly bind to the receptor site for glutamate, causing depolarization of neurons and calcium build-up. This will lead to nausea, vomiting, abdominal cramps, diarrhea, memory loss, decreased level of consciousness, seizures, confusion, disorientation, and possible death. This is more is commonly referred to as amnesiac shellfish poisoning (ASP). This has lead to irrational behavior among birds, and also to the death of over 400 sea lions.
Detection of P. australis, or any of its genus, can be difficult. The acid does not affect shellfish, crabs, and clams. Before, because of the nature of the silicon dioxide wall, the only real way of identifying the genus and species of different diatoms was by using scanning electron microscopy, However, this takes time , money, and the correct facilities to do. Because of the recent outbreaks of ASP, quicker, and hopefully cheaper, ways were needed. The two most common ways used now are whole cell hybridization and sandwich hybridization.
References
Herring, David. “What are phytoplankton?” http://earthobservatory.nasa.gov/Library/Phytoplankton/
Pkociolek. “Bacillariophyta” http://www.calacademy.org/research/diatoms/overview/introduction.html
Scottish Executive. “Harmful Algal Bloom Communities in Scottish Coastal Waters: Relationship to Fish Farming and Regional Comparisons” http://www.scotland.gov.uk/Publications/2006/02/03095327/3 2003
Shin, Jennifer. “Pseudo-nitzschia” http://www.mbari.org/staff/conn/botany/diatoms/jennifer/indexa.htm 1999
Van Wezel, Rene. “Series in Marine Phytoplankton: The genus Pseudo-nitzschia.” http://www.microscopy-uk.org.uk
*Disclaimer - This report was written by a student participaring in a microbiology course at the Missouri University of Science and Technology. The accuracy of the contents of this report is not guaranteed and it is recommended that you seek additional sources of information to verify the contents.
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