Scientist targets ultimate puzzle

By SIMON COLLINS

Auckland scientist David Saul has embarked on the ultimate detective quest - to use genetic techniques to track down the origin of life.

The Auckland University microbiologist has been awarded $475,000 from the Government's Marsden Fund to try to recreate a gene from the last common ancestor of all living things.

He and his team will test the hypothesis that life originated in hot conditions where the temperature might have been more than 100C.

Dr Saul, a Waiheke father of two who does the Herald cryptic crossword on the ferry each day, delights in the puzzle-solving power of genetics.

He says that studying the genes of thousands of organisms has enabled biologists to piece together a much more complete "tree of life", sorting all living things into genetically related families.

The size of that tree has ballooned since American scientist Norman Pace used the new genetic techniques to do "DNA fingerprinting" in the mud beneath a hot pool in the early 1980s.

"He found that we had observed less than 0.1 per cent of the micro-organisms out there," said Dr Saul.

"He found that we knew virtually nothing. We can't even quantify how ignorant we are, there is so much to learn.

"There is probably a greater biomass of micro-organisms under our feet than the biomass of all micro-organisms, plants and animals living on the surface."

Dr Saul and Dr Jackie Aislabie of Landcare have found tiny microbes in the driest, coldest and windiest place on Earth, the Dry Valleys of Antarctica.

Others have been found in rocks at high temperatures up to 10km underground.

"They live off rock and enjoy it," said Dr Saul. "They are living in ecosystems that are isolated from the surface organisms and may have been isolated for millions of years."

He believes these primitive creatures may provide clues to how life began soon after the sun and its planets formed out of molecular clouds 4.5 billion years ago. Carbon-dating of fossils has traced life back 3.8 billion years so far.

At that time, the Earth was surrounded by a dense layer of carbon dioxide, producing a kind of super-greenhouse effect.

Fragments of matter formed out of the original molecular clouds were still flying around the solar system, producing far more meteor strikes on Earth than we experience today.

"So the oceans were constantly being boiled," Dr Saul said.

"There was not any very stable environment except underground or at the bottom of the oceans."

His team plan to dig back into the roots of life by investigating a gene called leuB.

Overseas researchers have tried similar detective work.

But so far no one has tried digging as deeply into the family tree as Dr Saul proposes.

"We are going to slowly progress down a few branches, developing confidence in our methods," he said.

The ultimate goal is to determine the sequence of the leuB gene from what biologists call the "Last Universal Common Ancestor" (Luca).

When they find it, Dr Saul's team will use modern genetic engineering techniques to re-create the ancestral gene.

They will then splice it into bacteria, and use the bacteria to re-create the protein which that gene helped to form.

Finally, they will test the protein in a variety of temperatures to infer the heat of the environment in which Luca lived - possibly in a hydrothermal vent where hot water gushes out of undersea volcanoes.

"If I had to put my money on it, I'd say it was in a hydrothermal vent or deep underground in the rock," Dr Saul said.

He believes that life may have begun as just another chemical reaction among the many chemical processes that go on in such environments.

Somehow, one of those processes must have become "self-replicating" and extracted chemicals from the environment to build the first DNA, the complex molecule found in all living things which stores information about the organism's functions.

"If life started as a series of chemical reactions that were capable of self-replicating, then I think you have thrown a six in the game of life. You have got off square one on the board," said Dr Saul.

"What form that took, and where it occurred, we don't really know.

"But we can at least ask some questions about Luca, and if we can extend back through history in our experiments, even if we can't reach Luca, we can see in which direction evolution is occurring."