Microbial Source Contamination

Exploring how UMN researchers are using DNA technology to study fecal contamination in Minnesota waters


Kate Johns (Designer), Rachel Zussman (Writer)

Minnesota Lakes in Peril

Rachel Zussman (Writer)

UMN researchers use DNA technology to track fecal contamination in Minnesota waters

Imagine your next summer vacation: boating, fishing, or swimming in Minnesota lake country. After months of anticipation, you arrive at the lake to find the beaches closed and the water contaminated by fecal bacteria. Unfortunately, it’s not an isolated occurrence. According to the Minnesota Pollution Control Agency, 40% of Minnesota’s lakes and streams are impaired, and fecal contamination is a growing concern. A team led by University of Minnesota microbiologist Michael Sadowsky hopes to provide public health officials with better tools to track the source of contamination and assess the public health risk.

Fecal contamination has been a national issue for decades. In 1977, the US government adopted the Clean Water Act using coliform bacteria (and later the bacterium E. coli) as an indicator for fecal contamination of waterways. Commonly found in the intestinal tract of the warm-blooded animals, E. coli in the water suggested the possible presence of other fecal pathogens, and forced officials to close beaches out of an abundance of caution. As new research indicated that E. coli could survive in nature outside the gut, its value as an indicator of water quality waned. Researchers now focus on the source of bacteria to better assess the public health risks and eliminate contamination at the source.

Initially, Sadowsky’s team relied on a technique known as DNA fingerprint analysis to identify the source of fecal contamination. “We would go into the environment and collect ‘fingerprints’ of individual bacteria,” explains Sadowsky. “These ‘fingerprints’ would then be matched with E. coli bacteria obtained from feces of 17 animal species.” Though more accurate than older methods, DNA fingerprinting only worked about 75% of the time.

Improvements in DNA sequencing technology now allow Sadowsky’s team to analyze fecal samples from a large number of animal species. Using SourceTracker, a software program developed by the UMN Knights Lab, the team can compare the distribution of organisms in water samples with those found in the animals.

So far, Sadowsky has successfully identified contamination coming from a few sources. But since contamination often comes from both human and animal origin, making the source of the contamination harder to identify and remediate.

Though wildlife and agriculture add to the problem, Sadowsky believes that both point and non-point source microbial contamination are symptoms of urbanization. “We have cities with millions and millions of people,” he adds. “Every time you flush a toilet, that water has to go somewhere.”

As the technology continues to improve, Sadowsky hopes the research will help inform public policy. “I want to work with decision makers to establish water quality standards based on the source of contamination.”

Health risks depend on both the source and the level of fecal contamination. With better tools at their disposal, policymakers can continue to protect the public while residents and tourists continue to enjoy summer days on Minnesota’s 10,000 lakes.

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