19 May 1999
Aussie Toxin Eater Discovered
Australia's Commonwealth Scientific and Industrial Research Organisation (CSIRO) scientists have discovered a native Australian microbe that eats pesticide for breakfast - offering new hope for a way to clean up contaminated soil and water.
The microbe was identified from a polluted site in Perth by University of Western australia PhD researcher Ms Amanda Tilbury, working with microbiologist Dr Peter Franzmann of CSIRO Land and Water.
The microbe, a new strain of the well-known soil organism Pseudomonas, is equipped to degrade the world's most widely used herbicide, atrazine, says Ms Tilbury.
More than 300 tonnes of atrazine are sprayed on broadleaf and grassy weeds on farms and in cities across Australia. It is highly persistent and can hang around in the soil or water for years afterwards. Although listed as a possible human carcinogen, the big problem with atrazine is that it is highly toxic to water life. It has been implicated in a number of fish kills.
"It can also get into groundwater, and in some parts of the country groundwater is used for drinking - so we wanted to find a way of purifying the water while it was still underground," Ms Tilbury explains.
Examining soil from a site contaminated with atrazine in the Perth metropolitan area, she found at least 40 different kinds of bacteria. From these she selected four which appeared to have the ability to digest and neutralise the pollution.
But the standout strain, Pseudomonas AT2 (initialled after Amanda Tilbury), had the three vital genes that enable it to chomp through the atrazine in a matter of hours.
"Normally the atrazine would have a half-life in the groundwater as long as 8 years. In the laboratory, we reduced this to just five hours using AT2," she says.
"We hope to be able to spray or inject AT2 into any big spill or contamination by atrazine and so render it harmless. It may also be used to clean a farmer's soil so the atrazine residue has no effect on the next crop sown in the paddock."
The search for an atrazine muncher began with the CSIRO team testing a bug originally from the United States, Pseudomonas ADP, which was known to break down atrazine with reasonable efficiency.
However, preferring not to release an introduced soil microbe, they decided to see whether there were any native bacteria which would do as good a job.
The discovery was made in a 300 meter long plume of groundwater in the Swan river coastal plain, which was contaminated by spilled atrazine.
"Although soil bacteria from the site would never have encountered a man-made chemical like atrazine before, several of them have already evolved the ability to break it down in a relatively short time," says Ms Tilbury.
And her prize strain, AT2, did it considerably more reliably than the imported American bug. "It's a remarkable testimony to the richness of Australia's biodiversity. This microbe had somehow acquired all three of the genes needed to degrade atrazine" she says.
"The beauty is that the microbe itself is perfectly safe for humans, animals and plants."
Ms Tilbury is now experimenting to see what other forms of pesticide her microbe will break down.
"It chops chlorine atoms off a range of chemical molecules, and that makes them non-toxic," she says. "It is looking very promising as a way to break down the widely-used herbicides 2.4.5-T and 2.4-D."