Soil Inhabitants: Bacteria

Vital Statistics:Length: 0.001 - 0.005 mm (over 1,000 could fit across the head of a pin).
Lifespan: Divides into two new bacteria as often as every 20 minutes.
Total Bacterial Population: Up to 1,000 trillion per square meter (5 billion in one teaspoon of soil).

Description & Natural History:All life in the soil depends on its smallest residents. Single-celled bacteria are the oldest living things. And they power the entire ecosystem. They may have boring shapes, but they do ore different biochemical jobs than any other kind of organism.
Thousands of species of bacteria fill the soil. Most are decomposers. They recycle the energy stored in dead organic matter back into plant food. Other bacteria make nutrients with the help of host plants. For example, bacteria living in the roots of plants like peas and clover turn nitrogen from the air into fertilizer. A few bacteria can get energy from minerals instead of organic matter. Some of these can even feed on chemical pollution.
Bacterial colonies make slime that helps them stick to soil particles. The slime also sticks soil particles to each other. These goopy clumps help hold water in the soil. Plant roots can easily grow through the spaces between these clumps.
The familiar, earthy odor of rich, damp soil is the smell of bacteria at work.