Virus
Japanese: ウイルス
Tiny infectious particles composed of a protein coat and nucleic acid. Unable to replicate on their own, they parasitize host cells to reproduce. They exist at the boundary between living and non-living.
Viruses are entirely different from bacteria and fungi. They have no cells and cannot reproduce on their own. They enter a host cell and borrow its machinery to make copies of themselves.
Are they living or non-living? There is still no definitive answer. Viruses shake the very definition of life.
Though they have little direct involvement in fermentation, viruses called bacteriophages that infect bacteria can devastate cultured bacteria in the fermentation industry.