Giant viruses and their mobile genetic elements: the molecular symbiosis hypothesis

By providing fitness advantages to the virus in which they reside, these MGEs compose a kind of molecular symbiotic association in which both partners benefit from the presence of each other's. Thus, protective effects provided by some of these MGEs may have generated an arm race between competing GVs in order to encode the most diverse arsenal of anti-viral weapons, explaining the unusual abundance of MGEs in GV genomes by a kind of ratchet effect.