of archaea, bacteria, especially unicellular protists, yeasts, and at least arguably generally.
The viruses of microorganisms are grouped together much more in terms of the physical association of the cells they infect, which tends to be lacking, rather than .
On the other hand, even microorganisms can clump together , as into microocolonies. Nonetheless, what typically will be lacking are extracellular antiviral mechanisms in versus especially those seen in animals and plants.
Additional discussion of viruses of microorganisms can be found following these links: