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Trichodesmium

Trichodesmium is a biology topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Trichodesmium rather than just read about it. In short: 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 in the Red Sea, where they were first described by Captain Cook).

Trichodesmium — main illustration
Trichodesmium — illustration

Key takeaways

  • Trichodesmium belongs to biology; place it in that map before memorising details.
  • Learn the definition first, then one example that makes the definition concrete.
  • Connect Trichodesmium to a quantity you can measure, compute or draw — that is where exam questions come from.
  • Reproduce the core statement of Trichodesmium from memory before moving on to harder problems.

Reference excerpt

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 in the Red Sea, where they were first described by Captain Cook). Trichodesmium is a diazotroph; that is, it fixes atmospheric nitrogen into ammonium, a nutrient used by other organisms. Trichodesmium is thought to fix nitrogen on such a scale that it accounts for almost half of the nitrogen fixation in marine systems globally. Trichodesmium is the only known diazotroph able to fix nitrogen in daylight under aerobic conditions without the use of heterocysts. Trichodesmium can live as individual filaments, with tens to hundreds of cells strung together, or in colonies consisting of tens to hundreds of filaments clustered together. These colonies are visible to the naked eye and sometimes form blooms, which can be extensive on surface waters. These large blooms led to widespread recognition as "sea sawdust/straw". The Red Sea gets most of its eponymous colouration from the corresponding pigment in Trichodesmium erythraeum. Colonies of Trichodesmium provide a pseudobenthic substrate for many small oceanic organisms including bacteria, diatoms, dinoflagellates, protozoa, and copepods (which are its primary predator); in this way, the genus can support complex microenvironments.

Species There are currently 9 accepted species in the genus Trichodesmium:

Trichodesmium clevei (J.Schmidt) Anagnostidis & Komárek Trichodesmium contortum (Wille ex O.Kirchner ) Wille Trichodesmium erythraeum Ehrenberg ex Gomont Trichodesmium hildebrantii Gomont Trichodesmium iwanoffianum Nygaard Trichodesmium lacustre Klebahn Trichodesmium lenticulare (Lemmermann) Anagnostidis & Komárek Trichodesmium scoboideum A.H.S.Lucas Trichodesmium thiebautii Gomont Trichodesmium erythraeum, described by Ehrenberg in 1830, is the lectotype of the genus. T. erythraeum is the species responsible for discoloring the Red Sea during blooms. This is the only sequenced genome in the genus thus far and is the focus of most laboratory studies (Trichodesmium IMS 101).

Cell structure Like most cyanobacteria, Trichodesmium has a gram negative cell wall. Unlike other diazotrophic, filamentous cyanobacteria, Trichodesmium do not have heterocysts—structures found in some filamentous, nitrogen-fixing cyanobacteria which protect the enzyme nitrogenase from oxygen. This is a unique characteristic among filamentous cyanobacteria which fix nitrogen in daylight. Photosynthesis occurs using phycoerythrin – light-harvesting phycobiliprotein which is normally found within heterocysts in other diazotrophs. Instead of having localized stacks of thylakoids, Trichodesmium has unstacked thylakoids found throughout the cell. Trichodesmium is highly vacuolated and the content and size of the vacuoles shows diurnal variation. Large gas vesicles (either along the periphery as seen in T. erythaeum or found distributed throughout the cell as seen in T. thiebautii) allow Trichodesmium to regulate buoyancy in the water column. These gas vesicles can withstand high pressure, presumably those up to 100–200 m in the water column, allowing Trichodesmium to move vertically through the water column harvesting nutrients.

Nitrogen fixation N2 is the most abundant chemical in the atmosphere. However, diatomic nitrogen is not usable for most biological processes. Nitrogen fixation is the process of converting atmospheric diatomic nitrogen into biologically usable forms of nitrogen such as ammonium and nitrogen oxides. This process requires a substantial amount of energy (in the form of ATP) in order to break the triple bond between the nitrogen atoms. Trichodesmium is the major diazotroph in marine pelagic systems and is an important source of "new" nitrogen in the nutrient poor waters it inhabits. It has been estimated that the global input of nitrogen fixation by Trichodesmium is approximately 60–80 Tg (megatonnes or 1012 grams) N per year. Nitrogen fixation in Trichodesmium is unique among diazotrophs because the process occurs concurrently with oxygen production (via photosynthesis). In other cyanobacteria, N2 and CO2 reduction are separated either in space (using heterocysts to protect the sensitive nitrogenase enzyme from oxygen) or time. However, Trichodesmium lacks heterocysts and nitrogen fixation peaks during daylight hours (following a diel flux initiated in the morning, reaching a maximum fixation rate midday, and ceasing activity at night). Since the first realization of this enigma, Trichodesmium has been the focus of many studies to try and discover how nitrogen fixation is able to occur in the presence of oxygen production without any apparent structure separating the two processes. 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 phycobilisomes, with PSI and PSII.

Ecology

… excerpt ends here. Continue reading the full article.

Illustrations

Trichodesmium illustration
Trichodesmium: Illustration
Illustration
Trichodesmium: Trichodesmium erythraeum bloom, between Vanuatu and New Caledonia, SW Pacific Ocean.
Trichodesmium erythraeum bloom, between Vanuatu and New Caledonia, SW Pacific Ocean.
Trichodesmium: Examples of Trichodesmium colonies sorted into morphological classes(A) radial puffs, (B) non-radial puffs, (C) tufts.[11]
Examples of Trichodesmium colonies sorted into morphological classes(A) radial puffs, (B) non-radial puffs, (C) tufts.[11]
Trichodesmium: Colonies of marine cyanobacteria Trichodesmiuminteract with other bacteria to acquire iron from dust a. The N2-fixing Trichodesmium spp., which commonly occurs in tropical and sub-tropical waters, is of large environmental significance in fertilizing the ocean with important nutrients.b. Trichodesmium can establish massive blooms in nutrient poor ocean regions with high dust deposition, partly due to their unique ability to capture dust, center it, and subsequently dissolve it.c. Proposed dust-bound Fe acquisition pathway: Bacteria residing within the colonies produce siderophores (C-I) that react with the dust particles in the colony core and generate dissolved Fe (C-II). This dissolved Fe, complexed by siderophores, is then acquired by both Trichodesmium and its resident bacteria (C-III), resulting in a mutual benefit to both partners of the consortium.[12]
Colonies of marine cyanobacteria Trichodesmiuminteract with other bacteria to acquire iron from dust a. The N2-fixing Trichodesmium spp., which commonly occurs in tropical and sub-tropical waters, is of large environmental significance in fertilizing the ocean with important nutrients.b. Trichodesmium can establish massive blooms in nutrient poor ocean regions with high dust deposition, partly due to their unique ability to capture dust, center it, and subsequently dissolve it.c. Proposed dust-bound Fe acquisition pathway: Bacteria residing within the colonies produce siderophores (C-I) that react with the dust particles in the colony core and generate dissolved Fe (C-II). This dissolved Fe, complexed by siderophores, is then acquired by both Trichodesmium and its resident bacteria (C-III), resulting in a mutual benefit to both partners of the consortium.[12]

Worked examples

Example 1 — a first encounter with Trichodesmium

Start with the simplest possible case. Write down what Trichodesmium claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In biology, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Trichodesmium before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Trichodesmium ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Trichodesmium

In research
Trichodesmium appears in biology research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry
Engineering practice reuses Trichodesmium in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom
Trichodesmium is common in secondary-school and first-year university syllabi. It links to neighbouring topics Cyanobacteria genera, Oscillatoriales, so understanding it makes those chapters shorter.
In everyday life
Look for Trichodesmium outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.
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How to study Trichodesmium in 20 minutes

  1. Read the reference excerpt below once, without taking notes.
  2. Close the page and write down what Trichodesmium means in your own words.
  3. Compare your version with the excerpt and mark what you missed.
  4. Work through the three examples above with pen and paper.
  5. Explain Trichodesmium out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Trichodesmium in simple terms?

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 in the Red Sea, where they were first described by Captain Cook).

Why does Trichodesmium matter?

Because it connects several biology ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Trichodesmium?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Trichodesmium.

Tags

  • Cyanobacteria genera
  • Oscillatoriales

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