Nitrogen cycle

Write out the process for nitrification.

NH₃ → NH₂OH → NO₂⁻ → NO₃⁻

Where is the NH₃ coming from?

Organic material, nitrogen fixation, or nitrate reduction.

Which part is completed by AOB/AOA, and which part by NOB?

AOB/AOA: Ammonia oxidation; NOB: Nitrite oxidation.

Organisms performing nitrification are classified as ____, and get carbon from ____.

Chemolithoautotrophs; carbon from CO₂.

What is the electron donor and acceptor in nitrification?

ED → Ammonia; EA → Molecular oxygen (O₂).

Do nitrifiers generate or require energy for this process?

It generates energy (used for cellular work).

Write out the process for dissimilatory denitrification.

NO₃⁻ → NO₂⁻ → NO → N₂O → N₂

Where might the nitrate come from?

End product of nitrification.

What organisms are capable of denitrification?

Many types (diverse).

These organisms are classified as ____, and obtain carbon from ____.

Anaerobic respiring organisms (heterotrophs); organic sources.

What is the electron donor and acceptor in denitrification?

ED → NADH + H⁺; EA → NO₃⁻

Is nitrate reductase cytoplasmic or membrane bound?

Membrane-bound (interacts with proton motive force).

Does this process generate or require energy?

Generates energy.

Write out the process for assimilatory nitrate reduction.

NO₃⁻ → NO₂⁻ → NH₂OH → NH₃

Where might the nitrate come from?

Abiotically or from nitrification.

Does this process require or generate energy?

Requires energy.

Why would an organism perform assimilatory nitrate reduction?

To generate usable nitrogen for amino acids.

Can you determine the organism’s metabolism from this activity alone?

No, not without info on electron donors/acceptors.

Is nitrate reductase cytoplasmic or membrane bound here?

Cytoplasmic.

Write out the process for nitrogen fixation.

N₂ → NH₃

What enzyme is required for nitrogen fixation?

Nitrogenase.

Where is the N₂ coming from?

Atmosphere (sometimes soil).

What 2 compounds inhibit nitrogen fixation?

NH₃ and O₂.

What organisms are capable of nitrogen fixation?

Archaea and Bacteria (some free-living).

Does nitrogen fixation generate or require energy?

Requires energy ($$$).

Write out the process for anammox.

NO₂⁻ → NO → N₂H₄ → N₂ (NH₃ feeds in before N₂H₄)

Where does the NH₃ and NO₂⁻ come from?

NH₃ → Nitrate reduction or fixation; NO₂⁻ → AOB, AOA, or comammox.

What special structure is needed for this process?

Anammoxosome.

What organisms are capable of anammox?

Planctomycetes.

Does this process require or generate energy?

Generates energy.

What is the electron donor and acceptor in anammox?

ED → Ammonia; EA → Nitrite.

Would this organism be considered a lithotroph?

Yes, because it uses an inorganic donor.