Bacteria are little, but they reproduce quickly, and one bacterium can multiply into thousands or even millions of new bacteria in just a few hours. Bacteriophages are small viruses that can infect bacteria (phages). Bacteriophages are so tiny that they don't even have a single cell, instead consisting of a single strand of DNA encased in a protein sheath. Bacteriophages can expand rapidly when they infect a bacterium, causing the bacteria to burst and release a large number of new phages. The human body contains trillions of bacteria and bacteriophages, which are essential for a normal, healthy life. Bacteriophage research has become an important element of biology due to its ubiquitous existence and close ties with bacteria. Analyses of bacteriophage genome sequences allow researchers to uncover fundamental principles of genome organisation, co-evolution, and genome modelling and modification.
Mycoviruses, commonly known as mycophages, are fungi-infecting viruses. Mycoviruses have double-stranded RNA (dsRNA) genomes and isometric particles in the majority of cases, but about 30% have positive-sense, single-stranded RNA (+ssRNA) genomes. True mycoviruses have the ability to infect and spread to other healthy fungi. Many double-stranded RNA elements found in fungi do not suit this definition, and they are referred to as virus-like particles, or VLPs, in these circumstances.