The metagenome is the set of bacterial populations in a given environment. The method used to analyse - the metagenome - is to study genes collectively, without examining them individually.
This has the advantage of faster analysis and the principle is also ecologically relevant. The important information to obtain is which genes, and therefore which biological functions, are present in the environment.
The metagenomes are studied in marine, terrestrial and internal animal media (the bacterial ecosystems of these are called microbiomes) . For example, we are particularly interested in the human intestinal metagenome.