This article – by one of the discoverers of Mimivirus – argues that the new giant DNA viruses are different from other viruses and that as a result, we neew to create a new brach of microbes. Other virologists are more cautious, suggesting that Mimivirus can fit within the current scheme of virus taxonomy. Either way, this is a good read.
Mimivirus inaugurated in the 21st century the beginning of a reclassification of viruses. (2016) Current Opinion in Microbiology, 31, 16-24.
Mimivirus and other giant viruses are visible by light microscopy and bona fide microbes that differ from other viruses and from cells that have a ribosome. They can be defined by: giant virion and genome sizes; their complexity, with the presence of DNA and mRNAs and dozens or hundreds of proteins in virions; the presence of translation-associated components; a mobilome including (pro)virophages (and a defence mechanism, named MIMIVIRE, against them) and transpovirons; their monophyly; the presence of the most archaic protein motifs they share with cellular organisms but not other viruses; a broader host range than other viruses. These features show that giant viruses are specific, autonomous, biological entities that warrant the creation of a new branch of microbes.