Our environment is inhabited by micro-organisms.

Some of these develop during the composting process and play a role in breaking down organic matter.

The main examples are mesophilic and thermophilic bacteria, and fungi.

Below is a brief introduction.

>> Bacteria
Bacteria are the most important type of micro-organism for compost. They make up 80 - 90% of the billions found in a single gram of compost. They use a wide range of enzymes to break down organic matter chemically. During the first phase of composting, mesophilic bacteria predominate. When the temperature of the compost exceeds 40°C, the thermophilic bacteria take over. The diversity of bacteria is slightly greater when the temperature lies between 50 and 55°C, but quickly decreases above 60°C, when only thermophilic bacteria can survive.

>> Actinomycetes
These micro-organisms resemble fungi but are in fact filament-forming bacteria. In compost, they play an important role in the degradation of complex organic matter such as cellulose, lignin, chitin and proteins. Some species appear during the thermophilic phase of composting, while others appear during the cooling phase.

>> Fungi
Fungi are very important for compost because they decompose complex compounds and break down waste, thus allowing the bacteria to get on with decomposition. Fungi are abundant during the mesophilic and thermophilic composting phases.

>> Protozoa
Protozoa are single-cell eucaryotes (they have a true cell nucleus, unlike bacteria which do not have a nuclear membrane). They play a minor role in the decomposition of organic material.

>> Rotifera
Rotifera are miscroscopic multi-cellular organisms found in leachates and the water contained in compost.