Raw sewage: Home to millions of undescribed viruses

October 03, 2011

Biologists have described only a few thousand different viruses so far, but a new study reveals a vast world of unseen viral diversity that exists right under our noses. A paper to be published Tuesday, October 4 in the online journal mBio® explores ordinary raw sewage and finds that it is home to thousands of novel, undiscovered viruses, some of which could relate to human health.

Viruses are everywhere: every moment of every day, humans are exposed to viruses on surfaces, in foods, and in water. However, our knowledge of the viral universe is limited to a tiny fraction of the viruses that likely exist. There are roughly 1.8 million species of organisms on planet Earth, and each one is host to untold numbers of unique viruses, but only about 3,000 have been identified to date.

To explore this diversity and to better gauge the numbers of unknown viruses that are out there, researchers looked for the genetic signatures of viruses present in raw sewage from North America, Europe, and Africa.

They detected signatures from 234 known viruses that represent 26 different "families", or types, of viruses. This makes raw sewage home to the most diverse array of viruses ever found.

Known viruses included human pathogens like Human papillomavirus and norovirus, which causes stomach flu. Also present were several viruses belonging to those familiar denizens of sewers everywhere: rodents and cockroaches. Bacteria are also present in sewage, so it was not surprising that the viruses that prey on bacteria dominated the known genetic signatures. Finally, a large number of the known viruses found in raw sewage came from plants, probably owing to the fact that humans eat plants and plant viruses outnumber other types of viruses in human stool.

Raw sewage contains more mysteries than answers, however: the vast majority of viral genetic signatures belong to unknown viruses. This fact is significant, says the study's editor, Michael Imperiale of the University of Michigan. Unknown viruses like those found in sewage probably play many roles in human health and environmental processes that we simply do not appreciate yet, he says.

Of the unknown sewage viruses that come from humans, some of them may be opportunists that lie in wait for the human host's immune system to break down and provide an opening, he says.

Other viruses may be benign or even helpful. "There's a theory out there that we may be infected with viruses that don't cause any disease and may have beneficial effects," says Imperiale. There are examples of animal viruses that bear this out, he says, including a herpes virus in mice that makes them somewhat resistant to bacterial infections.

The study's authors plan to follow up their examination of sewage viruses with studies of other environments around the world where viruses are likely to thrive.

Michael Imperiale expects more discoveries to come. "I think this is going to be the tip of the iceberg of how many viruses are out there," he says. "I think the ocean is going to top raw sewage by orders of magnitude," although they won't be found in such densities as they are in sewage, he concedes.
-end-
mBio® is an open access online journal published by the American Society for Microbiology to make microbiology research broadly accessible. The focus of the journal is on rapid publication of cutting-edge research spanning the entire spectrum of microbiology and related fields. It can be found online at http://mbio.asm.org.

American Society for Microbiology

Related Diversity Articles from Brightsurf:

More plant diversity, less pesticides
Increasing plant diversity enhances the natural control of insect herbivory in grasslands.

Insect diversity boosted by combination of crop diversity and semi-natural habitats
To enhance the number of beneficial insect species in agricultural land, preserving semi-natural habitats and promoting crop diversity are both needed, according to new research published in the British Ecological Society's Journal of Applied of Ecology.

Ethnolinguistic diversity slows down urban growth
Where various ethnic groups live together, cities grow at a slower rate.

Protecting scientific diversity
The COVID-19 pandemic means that scientists face great challenges because they have to reorient, interrupt or even cancel research and teaching.

Cultural diversity in chimpanzees
Termite fishing by chimpanzees was thought to occur in only two forms with one or multiple tools, from either above-ground or underground termite nests.

Bursts of diversity in the gut microbiota
The diversity of bacteria in the human gut is an important biomarker of health, influences multiple diseases, such as obesity and inflammatory bowel diseases and affects various treatments.

Underestimated chemical diversity
An international team of researchers has conducted a global review of all registered industrial chemicals: some 350,000 different substances are produced and traded around the world -- well in excess of the 100,000 reached in previous estimates.

New world map of fish genetic diversity
An international research team from ETH Zurich and French universities has studied genetic diversity among fish around the world for the first time.

Biological diversity as a factor of production
Can the biodiversity of ecosystems be considered a factor of production?

Fungal diversity and its relationship to the future of forests
Stanford researchers predict that climate change will reduce the diversity of symbiotic fungi that help trees grow.

Read More: Diversity News and Diversity Current Events
Brightsurf.com is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to Amazon.com.