DNA Method Identifies Unknown Viruses in Reclaimed Water

Karyna Rosario, a Ph.D. student at the University of South Florida's College of Marine Science, used a novel technique to identify a full-range of unknown viruses in treated reclaimed water from plants in Pinellas and Manatee counties.

Her analysis was published recently in the journal Environmental Microbiology.

Rosario reports that none of the viruses are human pathogens, putting to rest the most serious of fears about humans using treated wastewater. But the study provides an important starting point for future research on viruses that survive the human body and are discharged into reclaimed water and how they might impact the environment.

Rosario, conducted the study under the tutelage of Professor Mya Breitbart, whose laboratory uses a technique for identifying previously unknown viruses based on their genetic material (DNA or RNA).

The study – “Metagenomic Analysis of Viruses in Reclaimed Water” – describes the method developed by Breitbart’s lab. Samples containing a host of viruses are processed to extract the virus’ DNA. The DNA is sequenced and then compared to existing databases of known DNA genomes to identify the viruses.

The difficulty for scientists, though, is that with millions of types of viruses in existence, there are still many more viruses that have yet to be identified and mapped. The process used in Breitbart’s lab also helps to identify never-before-seen viruses.

Rosario compared samples collected from effluent at a reclaimed water plant; reclaimed water coming from a public sprinkler; reclaimed water used at a plant nursery and drinking water from a plant nursery. She found reclaimed water contained 1,000-fold more virus-like particles than potable water and that reclaimed water may play a role in the dissemination of highly stable viruses.

The viral community was dominated by viruses that infect bacteria, but viruses related to animal, plant, and insect pathogens were also identified. She concluded that further studies are needed to evaluate the impacts of reclaimed water use on human and ecosystem health.

Reclaimed water is currently used in Florida for non-potable public water supply, crop irrigation, lawn watering, industrial uses and groundwater recharge. But an increasingly serious drought has led to some new considerations for using reclaimed water as a potential source of drinking water. This summer, the Tampa City Council voted to ask residents in a 2010 ballot question to consider whether highly treated reclaimed water could be returned to the city’s drinking water supply.

One of the biggest concerns about reclaimed water use is whether it carries and spreads pathogens, and until recently the microbiological content of reclaimed water was still largely unknown. Viruses are of particular concern because they include highly stable pathogens that can be resistant to standard wastewater treatment processes, Rosario explained, noting that for practical reasons, current quality control methods do not test the presence of pathogens directly and the spread of viral pathogens through reclaimed water remains a real possibility.

In Tampa, where 55 million gallons of treated wastewater a day is discharged into Tampa Bay, the safety of reclaimed water also has become a large environmental concern.

In the samples taken from the effluent and nursery irrigation systems ,viruses related to Rhinovirus – the cause of the human cold – were present, as well as Enterovirus, which is a large and diverse group of viruses which in some forms can cause human maladies, such as meningitis and foot and mouth disease. Similarities to cow, pig and monkey viruses also were identified in the samples.

The value of knowing that viruses exist in treated wastewater is that scientists now have a baseline list of what viruses are present.

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