Scientists have reached the first stage in a project to define and build a lifeform from scratch using manmade genes and chromosomes, which raises fresh ethical concerns about genetic engineering. The researchers have whittled down the number of necessary genes in the simplest known bacterium to discover which are the ones essential for the organism to survive and replicate.
The next stage is to synthesise the genes by machine, insert them into an artificial chromosome and add it to a chemical "soup" in which the genes can begin to orchestrate the replication of a novel lifeform.
In a study published today in the journal Science, the researchers detailed what they describe as the "minimal definition of life" for Mycoplasma genitalium, a bacterium which already has the smallest number of genes of any free-living organism.
Claire Fraser, a member of the team from The Institute of Genomic Research (TIGR) in Rockville, Maryland, said that the results of the study will form the basis of the next phase of the project, which is to synthesise a lifeform in the laboratory.
Her husband, Craig Venter of Celera Genomics, has already said that he would like to attempt to build a synthetic lifeform based on a knowledge of the minimum number of genes needed to sustain life.
"The bottom line is that out of the just over 500 genes in M. genitalium - the simplest free-living organism there is - we found that between 300 and 350 genes seem to be essential for growth," Dr Fraser said.
The scientists used a "knock-out" technique to eliminate certain genes in the bacterium to see if the lack of them affected its growth. They found that more than 30 per cent could be eliminated without any apparent affect.
By comparing the essential genes with those already known from other species of bacteria, the scientists were able to find out which genes were new. Dr Fraser said a third of the genes essential for life were not previously known.
"It was very humbling in the sense that it has made us realise that there is so much more to understand about life, which is far more complex than we thought," Dr Fraser said.
"We assume that the essential genes are carrying out fundamental biological processes, at least in the microbial world," she said.
A panel of bioethicists, writing in the same issue of Science, say the research raises questions about the meaning of life and the moral repercussions of creating novel lifeforms that could, for instance, be used in biological weapons.
"A minimal genome is generally defined as the smallest set of genes that allows for replication of the organism in a particular environment," say the Ethics of Genomics Group, led by Arthur Caplan of Stanford University.
"Although organisms developed from minimal genomes would not necessarily pose more of a risk than organisms engineered by current genetic engineering technology, this technology could accelerate the pace at which genetically modified organisms are developed," they say.
Reducing life to its simplest components - genes and DNA - has profound implications for ethical issues ranging from abortion to cloning, the ethicists say.
"If we extend the reductionism implicit in minimal genome research to a definition of human life, this has implications for the debate about whether stem cells, early embryos or hybrid embryos combining human DNA with cellular components of other species, are human," they say.
"Likewise, a genetic definition of when life begins would have implications for the abortion debate. We would argue that the complex metaphysical issues about the status of human beings cannot be discussed in terms of the presence or absence of a particular set of genes."