Hunt is on for bugs to clean up wastewater

Wanted: Bugs with strange tastes to eat arsenic before it flows into the Waikato River.

Scientists at the Institute of Geological and Nuclear Sciences' Wairakei laboratory are looking for an arsenic-eating bug to extract the toxic metal from the Wairakei geothermal power station's wastewater.

Arsenic levels in the Waikato River have increased ten-fold since the power station was built in 1958 and are now more than twice the maximum safe level for drinking.

Power station operator Contact Energy has to cut arsenic emissions as a condition of its consent for continuing to run the station until 2026.

Geothermal water is naturally high in arsenic and other minerals, which it dissolves from rocks as it rises to the Earth's surface.

The substance is one of the most lethal poisons known to human beings. But some of the bugs that survive in boiling geothermal springs have adapted to absorb it.

"We have a bug that likes to eat it," said geochemist Dr Bruce Mountain. But the bug does not keep arsenic in its body, so eventually it gets back out into the water.

Dr Mountain now leads a team of institute scientists searching for a bug that produces another chemical, such as sulphur, that will absorb arsenic permanently.

"Arsenic sticks to sulphur. That happens in nature, for example at Champagne Pool at Waiotapu," he said.

But it would be "very difficult" to make a bug do the same thing to order, Dr Mountain said. "It's not going to be an easy exercise, but it's certainly possible."

The institute has spent $700,000 on equipping its geomicrobiology laboratory with the kind of gene-identifying machines usually found in medical research centres.

Two microbiologists, Canadian Dr Peter Dunfield and Australian Dr Matthew Stott, have recently joined the group.

Both said they were attracted to Wairakei because of the unusual "extremophile" bugs that lived in its hot steam and water.

"Extremophiles are still a hot topic and New Zealand is certainly a great place to do this kind of work," Dr Dunfield said.

As well as searching for arsenic-eaters, the group is working with German researchers who drilled 150m into lignite and coal at Ohinewai, south of Auckland, last year to look for bugs living far below the Earth's surface.

Scientists believe single-celled microbes make up more than half of all living matter on the planet, and that more than half of those microbes live under our feet.

Dr Dunfield said attempts to trace the "family tree" of all modern life forms suggested that the original ancestor of all life - the first self-reproducing substance - may have been a heat-loving "thermophile" in the extremely hot water that exists deep underground and in geothermal outcrops such as Wairakei.

"The temperature increases the further down you go," he said. "At the moment there is no bacteria known to grow at more than 120C."

That is certainly extreme. But when life began, perhaps 3 billion years ago, conditions above ground were even less hospitable, with a thin atmosphere dominated by carbon dioxide and pounded by asteroids as the solar system took shape.

"There are other theories," Dr Dunfield said. "But the first living thing may have been a thermophile."