Keeping up with virus taxonomy: viruses that infect other microbes

Posted on January 12, 2021   by Laura Cox

Continuing the ‘Keeping up with virus taxonomy’ blog series, in this post we look at the viruses that infect fungi, bacteria and archaea.

Alphaflexiviridae

Viruses in the family Alphaflexiviridae are bendy, long and thin. There are over 50 known species of alphaflexiviruses, with seven genera. These viruses typically infect plants, but two species in this family can infect the pathogenic fungi Botrytis cinerea and Sclerotinia sclerotiorum. In particular, B. cinerea is an important disease-causing fungal pathogen in wine grapes and causes a grey coloured mould to form.It can render entire bunches, and sometimes entire vines of grapes unusable.

Botourmiaviridae

Alphaflexiviridae are not the only fungus-infecting family of viruses we will be discussing in today’s blog. Botourmiaviruses infect fungi and plants. Viruses in this family usually look like flattened circles (a shape also known as bacilliform). These viruses replicate in the cytoplasm of the cell and use RNA to replicate. Three of the four genera in this family infect fungi.

Herelleviridae

It is not only fungi that viruses are able to infect; viruses can infect a wide range of microbes. For example, viruses in the family Herelleviridae can infect bacteria. Bacteria-infecting viruses are known as bacteriophage – phage for short – and herelleviruses infect bacteria in the Firmicutes phylum.

Spiraviridae

Archaea are a group of micro-organisms that are similar to, but evolutionarily distinct from bacteria and are often found in extreme environments. Aeropyrum is a genus of archaea that thrive in extremely high temperatures. This heat tolerance does not make them resistant to viral infection, however. Spiraviridae is a family of viruses that are capable of infecting Aeropyrum. These hollow, rod-shaped virus particles cause chronic infection in the archaea they invade without bursting the cell.

Chrysoviridae

Chrysoviruses are small, isometric particles able to infect fungi, plants and possibly some insects.

When pathogenic fungi are infected by viruses in this family, something called hypovirulence occurs. The infected fungi become less virulent – their ability to infect, grow or produce spores is reduced. This is particularly important in the fungus Aspergillus fumigatus, which is an important fungal disease in people and causes a serious lung disease in people with a weakened immune system.

Other blogs in the series:

Keeping up with virus taxonomy
Biopesticides, African swine fever and plant diseases
Small viruses, extra small viruses and a virus used to protect against fungal disease
Rod-shaped viruses, cancer-associated viruses and the viruses that infect archaea