Integrated Calendar

Viruses and/or virus-like selfish elements are associated with all cellular life forms and are the most abundant biological entities on Earth, with the number of virus particles in many environments exceeding the number of cells by one to two orders of magnitude. The genetic diversity of viruses is commensurately enormous and might substantially exceed the diversity of cellular organisms. Unlike cellular organisms with their uniform replication-expression scheme, viruses possess either RNA or DNA genomes and exploit all conceivable replication-expression strategies. Although viruses extensively exchange genes with their hosts, there exists a set of viral hallmark genes that are shared by extremely diverse groups of viruses to the exclusion of cellular life forms and underlie the cohesiveness and autonomy of the virus world. Multiple evolutionary connections exist between viruses and non-encapsidated selfish genetic elements, such as plasmids and transposons. All these selfish elements intimately interact with cellular hosts, engaged in both cooperation and arms races, and I will argue that this Greater Virus World is a defining factor in the evolution of all life forms.

Giant viruses infecting protists have recently attracted enormous amount of fascinated attention, especially following the discovery of Pandoraviruses with their 2 megabase genomes exceeding in size the genomes of numerous cellular organisms. Speculations have been entertained on the origin of giant viruses (and by inference, possibly, all viruses) from an extinct 4th (and possibly, 5th, 6th etc) domains of cellular life. I will present evidence that the two groups of giant viruses, Pandoraviruses and Mimiviruses, have independently evolved from much smaller viruses via accretion of numerous genes from different sources. These viruses are an integral part of the Virus World not degenerate cells.