Anabaena azollae | A living Fertilizer fectory

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This isn’t just any plant-microbe relationship.

The partnership between Azolla and Anabaena azollae is one of the most efficient and tightly co-evolved symbioses known in the natural world. It’s a textbook case of mutualism—but with real-world consequences for agriculture, climate resilience, and sustainable farming.

🧬 Who Is Azolla?

Azolla is a small, fast-growing aquatic fern that floats on the surface of freshwater bodies. It forms dense green mats and is often found in warm, stagnant or slow-moving waters—especially in rice paddies across Asia.

Azolla filiculoides

But here’s the amazing part: within each leaf of Azolla, there are tiny, pocket-like cavities. And inside each cavity lives a population of Anabaena azollae.

It’s like the fern has built an apartment complex specifically for cyanobacteria—and A. azollae has moved in for good.

🤝 What Does the Partnership Look Like?

It’s a true mutualism:

• Azolla provides shelter: Inside its specialised leaf cavities, A. azollae is protected from environmental stress and competition.

• Azolla also supplies carbon: Through photosynthesis, Azolla releases carbohydrates that help fuel its microbial partner.

• Anabaena azollae provides nitrogen: In return, it fixes atmospheric nitrogen into ammonia, a form Azolla can absorb and use to grow—especially in nitrogen-deficient waters.

Here’s the real kicker:

Azolla cells along with Anabaena spp.

taken at KKM lab

This isn’t just a helpful relationship, it’s an obligate one.

Over evolutionary time, Anabaena azollae has lost its ability to live outside Azolla. Its genome has shrunk, offloading some critical functions to the host plant. Think of it as nature’s version of a permanent job contract—with no exit clause.

🌱 Why This Is Revolutionary for Agriculture

The Azolla-Anabaena azollae symbiosis means that:

• Azolla can grow rapidly without fertiliser, even in poor soils.

• It naturally enriches water and soil with nitrogen, making it an ideal green manure.

• When Azolla decomposes, that fixed nitrogen becomes available to crops like rice.

In short: this floating fern-and-bacteria duo works like a living fertiliser factory, right in the field.