Common Soil Bacteria

Healthy soil teems with many different species and strains of bacteria. Many bacteria are essential in breaking down organic matter; others provide vital nutrients to plants. Several common groups of bacteria are especially important to ensure the health of your soil.

Types

• Actinomycetes are an especially important group. They are responsible for the smell of fresh soil. Nitrogen-fixers like rhizobium make ammonia out of atmospheric nitrogen, while nitrifying bacteria turn the ammonia from the nitrogen-fixers into nitrates that plants can use. Some bacteria like Pseudomonas fluorescens help to keep harmful organisms like parasitic fungi in check.

Function

• Because plants derive nutrients from the soil, bacteria like nitrogen-fixers are key to plant health. Actinomycetes and decomposers also increase nutrient levels in the soil by breaking down the remains of other organisms. Bacteria like Pseudomonas fluorescens that form mutualistic relationships -- associations where both parties benefit -- can help keep plants healthy.

Features

• Some common soil bacteria form symbiotic associations with plants. Certain nitrogen-fixers, for example, live in the root nodules of legumes like soybeans. Others form characteristic structures. Actinomycetes, for example, form filament-like chains that resemble the hyphae of fungi.