The viriosphere, diversity, and genetic exchange within phage communities.

Natural phage communities are reservoirs of the greatest uncharacterized genetic diversity on Earth. Yet, identical phage sequences can be found in extremely different environments, which implies that there is wide circulation of viral genes among distantly related host populations. Further evidence of genetic exchange among phage and host communities is the presence in phage of genes coding for proteins that are essential for photosynthesis. These observations support the idea that a primary role of host populations in phage ecology and evolution is to serve as vectors for genetic exchange.