Читать книгу Parasitology - Alan Gunn - Страница 40

Viruses are not usually considered to be living entities and therefore do not have a kingdom of their own. This, however, is a hotly debated topic. For example, although Moreira and Lopez‐Garcia (2009) argue strongly against viruses being living entities, Koonin and Starokadomskyy (2016) consider the very question of whether viruses are alive to be unscientific because the definition of what one means by life is arbitrary. Didier Raoult and his co‐workers argue that the giant viruses called nucleocytoplasmic large DNA viruses (NCLDVs) should be considered as an additional distinct domain of living organisms (Boyer et al. 2010). NCLDVs are so large that they can be mistaken for bacteria, and their genomes are typically twice the size of other viruses. The suggestion that a specific group of viruses might be living organisms has generated a great deal of controversy for which no resolution is in sight. Nevertheless, phylogenetic analysis suggests that NCLDVs evolved before modern eukaryotes, that is, before the organisms that are their current hosts. Furthermore, they may have been the source of two DNA‐dependent RNA polymerases and a DNA topoisomerase that are found in modern eukaryotes (Guglielmini et al. 2019).