By BBC News Online Science Editor Dr David Whitehouse

Researchers believe that the simplest living thing on Earth would be a bacterium with between 265 to 350 genes. It is an organism that does not exist in nature - but we may be able to build it.

If such an artificial microbe could be made from non-living DNA molecules - and that is by no means certain - it may tell us something very profound about the nature of life.

There are some researchers who would like to conduct this experiment but they have asked for a public debate on the idea. Although they can see the scientific benefits of pursuing such a project, they recognise that many people will reject the project as a step too far.

"How dare scientists imagine they can create life," some will say.

The scientists say they want to avoid what they regard as the hysterical reaction that greeted the arrival of Dolly the sheep and the subsequent speculation about human cloning.

The idea for an artificial microbe is based on research just published in Science by researchers from the Institute for Genomic Research in the US.

They have examined the smallest-known bacterium called Mycoplasma genitalium which has just 480 genes. By successively disrupting these genes and seeing whether the microbe could stay alive, they have established what must be very close to the minimum set of molecular instructions to sustain life.

It comes down to about 265-350 genes and the way they work together to build proteins and the other chemicals that form the organism's structure, metabolism and self-repair mechanisms could help us to fill in some major gaps in our biological knowledge.

At least 100 of the genes are a complete mystery to science - we have no idea what function they support. This should be taken as something of a wake-up call. If these genes are so important to the proper operation of the cell and we do not know what they do, it means we still have a long way to go before we fully understand cellular life - and that includes humans.

It is going to be extremely difficult to find the cures for big diseases like cancer unless we start to get hold of some of this information.

Simple machines

But could an artificial organism really tells us what we need know and is such a creation even possible?

Scientists have already assembled the simpler virus this way but in a fundamental sense a virus is not alive. It is a type of parasite, as it needs a host cell to live.

The experiment to create a living organism from its basic chemical building blocks would be the culmination of science's view, held by the ancient Greeks and again since the renaissance, that living things are simply machines.

It is a view of life that will upset many. You could say the big question is whether higher animals like ourselves are just more complicated than bacteria or fundamentally different.

Humans are, of course, very different from bacteria in many ways. We have 100,000 genes not just a few hundred. With our gene set, or genome, comes a larger and more complicated body with a sophisticated brain.

Our brains give us self-awareness and the ability to reason and make decisions, to have self-will, to do science and to wonder about things. But if we can create life in the lab from scratch, will it alter our view of what we are? Will we, in a sense, have become Gods?