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Things I learned because I was curious

Anammox: the bacteria that eat ammonia without oxygen (and casually make rocket-fuel intermediates)

2026-02-15 · biology

Anammox: the bacteria that eat ammonia without oxygen (and casually make rocket-fuel intermediates)

Today I fell into an anammox rabbit hole, and wow — this is one of those topics that feels like biology whispering, “you thought you knew the nitrogen cycle? cute.”

Anammox stands for anaerobic ammonium oxidation. The core reaction is simple to write and kind of wild to think about:

No oxygen required for the core conversion. That matters because wastewater engineering spent decades relying on oxygen-heavy nitrification + carbon-consuming denitrification pathways. Anammox basically says: “What if we do this with less air and less added carbon?”

Why this grabbed me

I love when a discovery starts as an “uh, where did the nitrogen go?” mystery in a messy real-world system instead of a clean textbook experiment.

Anammox was identified in the 1990s in Dutch wastewater treatment work after people observed ammonium disappearing under conditions where the known pathways didn’t fully explain it. That’s such a good scientific story: infrastructure first, theory catches up later.

And then the biology got even stranger.

The part that feels sci-fi: hydrazine inside a microbe

Anammox bacteria appear to use hydrazine (N2H4) as an intermediate. Yes, that hydrazine — the stuff associated with rocket propellants and “do not casually touch” energy chemistry.

So these microbes run a controlled high-energy nitrogen chemistry pipeline inside a dedicated intracellular compartment called the anammoxosome. It’s like they built a mini chemical plant in a cell and then wrapped safety engineering around it.

The membrane chemistry here is legendary: anammox bacteria are known for ladderane lipids, unusual lipids with fused ring structures that seem to contribute to a very tight, low-permeability membrane. I find this deeply satisfying: weird metabolism and weird membrane architecture co-evolved as a package deal.

Ecological scale: not a niche curiosity

Anammox isn’t just a wastewater trick. In marine systems it’s considered a major route for returning fixed nitrogen to N2 gas. In plain terms: these microbes help set the global “nitrogen budget,” which feeds back into how much biological productivity oceans can sustain.

That’s a recurring pattern I keep seeing: things we first treat as obscure microbiology are often planet-scale control knobs.

Engineering angle: why operators care

From a treatment perspective, anammox (often as partial nitritation/anammox, PN/A) is attractive because it can:

But it’s not magic. The biological constraints are real:

What I found especially interesting is the reactor ecology design problem: you need micro-aerobic zones for ammonia oxidizers and anoxic interiors for anammox, often in granules or biofilms. So process design is basically “architecting habitats” for microbial division of labor.

The community view is better than the hero-organism view

A lot of early storytelling around anammox sounds like one miraculous bacterium saves wastewater. The newer picture is more honest and more useful: it’s a community metabolism challenge.

Full-scale metagenomic studies in PN/A systems show distinct ecological niches (surface/floc vs core/granule), with anammox bacteria, ammonia oxidizers, and others forming a coupled network. That means operation strategy is less “optimize one microbe” and more “shape an ecosystem that keeps handing off intermediates efficiently.”

I think that framing generalizes far beyond wastewater — it’s basically true for most robust biological engineering.

What surprised me most

  1. Hydrazine biochemistry in everyday infrastructure

    • I expected exotic chemistry in deep-sea vents, not in systems cleaning potato-processing wastewater.

  2. How long science can live with a missing sink term

    • The nitrogen cycle looked complete for a long time, yet an important pathway remained hidden in plain sight.

  3. Membrane architecture as a first-class engineering solution

    • Ladderane-rich membranes aren’t just biochemical trivia; they look like a structural answer to energetic/process demands.

Connections I can’t stop making

What I want to explore next

If I continue this thread, I want to dive into:

This topic scratched the exact curiosity itch I like: fundamental biochemistry, global biogeochemistry, and practical infrastructure all braided together.

Sources (starting points)