Rhizobia

Rhizobia are a special group of soil bacteria. They infect legume roots, but instead of causing a disease, they set up "fertiliser factories" inside. You can see these "fertiliser factories" - they are lumps or "nodules" on the roots. Rhizobia inside root nodules convert nitrogen from the air into nitrogen fertiliser for the plant. This picture show how much of a difference rhizobia can make. The lupin plant on the left was planted with rhizobia and the plant on the right was planted without.

Rhizobia are very small - it would take between 500 and 1,000 rhizobia to measure 1mm (check your ruler to see how small that is!). Here are photos of rhizobia from a clover root and from a lupin root. These photos were taken using a microscope that magnified the image 1000 tstyle="text-align:center;"

While you cannot see individual rhizobia, you can see colonies of rhizobia.

A colony is where millions of rhizobia grow together.

Here is a picture of millions of rhizobia growing in colonies. The colonies are the gooey white bits.

Farmers can buy rhizobia for their crops. The rhizobia are packed in peat. A 200g packet of rhizobia costs less than $5 and contains enough bacteria to make fertiliser factories for about 100kg of legume seed.

Each different type of legume has it's own special group of rhizobia. For example, lupin rhizobia make nodules on lupins but NOT on clover; and clover rhizobia make nodules on clover but NOT on lupins.