Trichodesmium
Encyclopedia
Trichodesmium, also called sea sawdust, is a genus of filamentous
cyanobacteria. They are found in nutrient poor tropical and subtropical ocean waters (particularly around Australia
and the red sea
, where they were first described by Captain Cook). Trichodesmium fixes atmospheric nitrogen
into ammonium, usable also for other organisms. While far from the only nitrogen fixing bacteria, they are among the most important of the marine varieties, and are being extensively studied for their role in nutrient cycling in the ocean. Unlike other nitrogen fixing bacteria, Trichodesmium does not have heterocyst
s, nor any other specialised cells for this task. Furthermore, nitrogen fixation peaks at mid-day, i.e. occurs during the same time as photosynthesis. Inhibitor studies even revealed that photosystem II activity is essential for nitrogen fixation in this organism. All this may seem contradictory at first glance, because the enzyme responsible for nitrogen fixation, nitrogenase
, is irreversibly inhibited by oxygen. However, Trichodesmium utilises photosynthesis
for nitrogen fixation by carrying out the Mehler reaction, during which the oxygen produced by PSII is reduced again after PSI. This regulation of photosynthesis for nitrogen fixation involves rapidly reversible coupling of their light-harvesting antenna, the phycobilisome
s, with PSI and PSII. Trichodesmium forms blooms and provides substrate for many small oceanic organisms (bacteria
, diatoms, dinoflagellates, protozoa
, and copepods).
Filamentation
Filamentation is the anomalous growth of certain bacteria, such as E. coli, in which cells continue to elongate but do not divide . Bacterial filamentation is often observed as a result of bacteria responding to various stresses, including DNA damage or inhibition of replication...
cyanobacteria. They are found in nutrient poor tropical and subtropical ocean waters (particularly around Australia
Australia
Australia , officially the Commonwealth of Australia, is a country in the Southern Hemisphere comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands in the Indian and Pacific Oceans. It is the world's sixth-largest country by total area...
and the red sea
Red Sea
The Red Sea is a seawater inlet of the Indian Ocean, lying between Africa and Asia. The connection to the ocean is in the south through the Bab el Mandeb strait and the Gulf of Aden. In the north, there is the Sinai Peninsula, the Gulf of Aqaba, and the Gulf of Suez...
, where they were first described by Captain Cook). Trichodesmium fixes atmospheric nitrogen
Nitrogen fixation
Nitrogen fixation is the natural process, either biological or abiotic, by which nitrogen in the atmosphere is converted into ammonia . This process is essential for life because fixed nitrogen is required to biosynthesize the basic building blocks of life, e.g., nucleotides for DNA and RNA and...
into ammonium, usable also for other organisms. While far from the only nitrogen fixing bacteria, they are among the most important of the marine varieties, and are being extensively studied for their role in nutrient cycling in the ocean. Unlike other nitrogen fixing bacteria, Trichodesmium does not have heterocyst
Heterocyst
Heterocysts are specialized nitrogen-fixing cells formed by some filamentous cyanobacteria, such as Nostoc punctiforme, Cylindrospermum stagnale and Anabaena sphaerica, during nitrogen starvation. They fix nitrogen from dinitrogen in the air using the enzyme nitrogenase, in order to provide the...
s, nor any other specialised cells for this task. Furthermore, nitrogen fixation peaks at mid-day, i.e. occurs during the same time as photosynthesis. Inhibitor studies even revealed that photosystem II activity is essential for nitrogen fixation in this organism. All this may seem contradictory at first glance, because the enzyme responsible for nitrogen fixation, nitrogenase
Nitrogenase
Nitrogenases are enzymes used by some organisms to fix atmospheric nitrogen gas . It is the only known family of enzymes that accomplish this process. Dinitrogen is quite inert because of the strength of its N-N triple bond...
, is irreversibly inhibited by oxygen. However, Trichodesmium utilises photosynthesis
Photosynthesis
Photosynthesis is a chemical process that converts carbon dioxide into organic compounds, especially sugars, using the energy from sunlight. Photosynthesis occurs in plants, algae, and many species of bacteria, but not in archaea. Photosynthetic organisms are called photoautotrophs, since they can...
for nitrogen fixation by carrying out the Mehler reaction, during which the oxygen produced by PSII is reduced again after PSI. This regulation of photosynthesis for nitrogen fixation involves rapidly reversible coupling of their light-harvesting antenna, the phycobilisome
Phycobilisome
Phycobilisomes are light harvesting antennae of photosystem II in cyanobacteria, red algae and glaucophytes.- General structure :Phycobilisomes are protein complexes anchored to thylakoid membranes. They are made of stacks of chromophorylated proteins, the phycobiliproteins, and their associated...
s, with PSI and PSII. Trichodesmium forms blooms and provides substrate for many small oceanic organisms (bacteria
Bacteria
Bacteria are a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria have a wide range of shapes, ranging from spheres to rods and spirals...
, diatoms, dinoflagellates, protozoa
Protozoa
Protozoa are a diverse group of single-cells eukaryotic organisms, many of which are motile. Throughout history, protozoa have been defined as single-cell protists with animal-like behavior, e.g., movement...
, and copepods).
External links
- Charles Darwin's description of sailing through a Trichodesmium bloom
- Trichodesmium in Florida — 2004, Florida Fish and Wildlife Conservation Commission Fish and Wildlife Research Institute