Dr Craig Venter - the man behind the privately funded human genome sequence - and Dr Hamilton Smith - a Nobel-Prize-winning geneticist - want to create a man-made microbe with the minimum number of genes needed to sustain life.

The project has received $3m from the Office of Science at the Department of Energy in the US and preliminary work is already under way.

If successful, this experiment, the scientists claim, will be the first step to developing new cost-effective energy sources. This could mean artificial bugs engineered to pump out vast quantities of hydrogen to power cleaner cars.

Safety and Ethics

In recent years, scientists have improved their ability to manufacture to order long chains of DNA - the so-called "code of life" - in the laboratory.

This skill makes it theoretically possible to synthesise the genetic material necessary to drive and maintain a very simple organism - a small bacterium.

Dr Venter first proposed the idea of creating an artificial bug in the lab in 1999. It raised a number of ethical and safety issues and any attempt to create the lifeform was then put on hold while these were debated.

Of particular concern is the potential of this type of technology to be used to develop new biological weapons. Publishing only limited details about the work could ease worries.

There is also concern about the danger to human health from a man-made organism escaping into the environment.

However, the scientists say they would exclude certain genes to make the new microbe safe.

The organism would be rendered incapable of infecting humans and would die if it ever escaped its petri dish, they say.

New chromosome

A panel of ethicists and religious leaders - brought together at Dr Venter's request - have been discussing the ethical implications of creating artificial life for a number of years.

Craig Venter: Wants to know more about the fundamental working of a cell

They concluded that if the ultimate goal was to benefit mankind and if all appropriate safeguards were followed, the project could be regarded as ethical.

The research will use a single-celled organism called Mycoplasma genitalium as a "template" for the new lifeform.

M. genitalium, which is normally found in the human genital tract and lungs, has the smallest known genome - just 517 genes. But work on the microbe has shown just 265 to 350 of these genes are essential for it to live.

Energy sources

Drs Venter and Smith will do their research at the Institute for Biological Energy Alternatives.

Dr Venter said: "With fossil fuel consumption continuing to rise and with it serious environmental damage to our planet, it is imperative that we explore alternative ideas to abate this situation."

The goal is to find cost-effective and efficient biological energy sources.

Several research groups are now looking into this. For example, searches are being undertaken to try to find microbes in the environment that produce large quantities of the gas fuel hydrogen as a byproduct of their natural biological processes.

Dr Venter is also engaged in this search but he plans to go a step further by trying to create a microbe specifically designed for the task.

"We could potentially engineer an organism with the ideal qualities to begin to cope with our energy issues," Dr Venter said. This might also include novel bacteria that are very good at taking the greenhouse gas carbon dioxide out of the atmosphere.

The first step though is making an artificial chromosome - the structure into which the scientists would pack their synthetic genome.

The research team plan to remove all of the M. genitalium bacterium's own genetic material and replace it with the man-made chromosome.

This new chromosome will contain about 300 genes. If the experiment works then the new cell will be able to divide and produce a new generation of cells. Ultimately, the research could lead on to a fully artificial lifeform built from scratch.

Artificial virus

The first synthetic virus was assembled earlier this year by another team of researchers in the US.

It was built from scratch using the genome sequence from the polio virus. But there was much debate at the time over whether it could be classified as a true lifeform.

Most scientists do not regard viruses as "living" because they need host cells in which to perpetuate themselves.

This latest project has funding to allow it to run initially for three years.

However, the development of the new bacterium could take much longer.

M. genitalium image by Frantz, Albay and Bott from University of North Carolina, Chapel Hill, US.