DNA tests to aid estuary clean-up

The work will determine the sources of bacteria in river water

Scientists are to use DNA testing to track microbes found in UK estuaries back to their original sources.

The work could help clean up the UK's estuaries for bathers and keep shellfish bred in farms healthier.

University of Exeter researchers say their new study will help determine how farm animal slurry and human waste contribute to river pollution.

They will first focus on E.coli bacteria, using tiny changes in their genomes to determine their origins.

Escherichia coli, or E.coli, is a bacterium that lives in the intestines of humans and animals and are expelled in faeces. Most strains are harmless, but some can cause illness.

"Over the previous 20 years, legislation aimed at improving water quality has been tackled by looking at point sources, i.e. a sewage works or a known pipe that feeds into the river," Dr Jon Porter, director of the project's microbiology team told BBC News Online.

"Under new [EU] legislation, we're going to have to look at diffuse sources of pollution - those sources where it's difficult to determine exactly where it's coming from."

"Our work is aimed at characterising the original host animal for the E.coli and on the basis of that help inform the management plan. Should we be targeting the farmers? Should we be targeting sewage treatment works?

"If we were to target farmers, should we be targeting sheep or cattle?"

Detective work

In the case of farmers, Dr Porter stressed that the work would not identify individual farms, it would simply inform guidelines already in use for managing slurry.

These could include controlling how close to a river farmers are allowed to spread slurry and the times of year it is spread.

The researchers are using routine methods for analysing DNA, but hope to refine their understanding of the subtle differences in genetic make-up that distinguish populations of E.coli found in human guts from those living in the cows, pigs and others.

This information will then be used to build up a database. The researchers hope to spend one year studying the river Exe and a further two years studying the river Helford in Cornwall.

University of Exeter scientists eventually plan to use this analysis with other bacteria and viruses from sewage that can be found in river water.

The work will also help control pathogens in mussel and oyster farms, where water quality is regularly tested and which can be shut down if pollution levels are found to be above certain agreed limits.

Tim Robbins of Devon Sea Fisheries commented:

"[The] scientists have the potential to detect whether it is human or animal sewage which is infecting our shellfish.

"This will lead to scientific statistics which will create more informed estuary management and cleaner waters. If the Helford project is successful the techniques could be rolled out across western Europe."

A teaming of biologists and geographers will help tie bacterial sources and the sediments in which they are found to an origin within a 10-20km area.

The project is part of a larger European Union river management programme called Cycleau.