http://news.bbc.co.uk/hi/english/sci/tech/newsid_556000/556984.stm
Scientists call for life creation debate
By BBC News Online Science Editor Dr David Whitehouse
Scientists have found the essence of life - at least on a genetic level -
and it comes down to about 300 genes.
US researchers think this is the minimum set of molecular instructions
required to build a living organism.
It has been suggested that this could be tested by trying to synthesise an
artificial bacterium in the lab - for scientists to create life from
non-living chemicals.
The idea is currently the subject of an ethical review and the scientists
involved say no attempt will be made to proceed with the daring experiment
until there has been a full and public debate.
The prospect of "scientists playing God", as some will undoubtedly see it,
is bound to provoke some fierce arguments.
Tiny organism
A team from the Institute for Genomic Research (Tigr) in Maryland pared-down
the tiniest-known living organism, a bacterium called Mycoplasma genitalium,
to its essential genes.
M. genitalium is the smallest-known bacterium
"The analysis suggests that 265 to 350 of the 480 protein-coding genes of M.
genitalium are essential under laboratory growth conditions, including about
100 genes of unknown function," the Tigr scientists have reported in the
journal Science.
The existence of 111 unknown but essential genes suggests that biologists do
not yet understand everything about basic life functions, they add.
M. genitalium lives in the human genital tract and lungs, causes no known
disease, but has fewer genes than any other known living thing. Humans have
between 80,000 and 140,000 genes, but M. genitalium has just 480.
Dr Craig Venter, founder of Tigr and now head of the Celera Genomics
Corporation, said the study was redefining life in terms of the genome, the
collection of all a creature's genes.
Essential genes
"Will we eventually get to a molecular definition of life? I hope that will
happen, yes," he told the BBC.
M. genitalium has a close relative, Mycoplasma pneumoniae, that has the same
480 genes as M. genitalium, plus 200 extra ones. "So we decided these genes
were not essential to life," Venter said.
One by one, the team disrupted the genes in M. genitalium to see which ones
the organism could not live without. They did this using transposons, which
are stretches of DNA that insert themselves into genes. The number found to
be essential was not exact, but close enough, the Tigr team said.
Most interesting is the large number of genes that are necessary, but about
which the researchers have no idea what they do.
"Our results imply that of the 111 genes of unknown function that have not
been disrupted in our experiments, the majority are essential," the
researchers wrote.
"The presence of so many genes of unknown function among the essential genes
of the simplest known cell suggests that all the basic molecular mechanisms
underlying cellular life may not yet have been described."
Much to learn
The study also established that some genes were only essential in certain
circumstances, when, for example, particular nutrients were denied to the
microbe. Dr Venter told the BBC: "We realised that life is context
sensitive. It does not exist on its own. It has to interact with its
environment."
The researchers have suggested the next step would be to create an
artificial bacterium, based on the essential genes. The first step in such
an experiment would be to build an artificial chromosome to carry the genes.
"We are not going to carry out this experiment until there has been a
broader debate on the issue," Dr Venter said. "Technically we would need to
synthesise a genome and see if it led to a living organism.
"It would clearly be creating a new species of life that does not exist. I
think if we could get down to the point of truly understanding and having
one of the formulas for life - and you have to understand that there are
thousands if not millions of different formulas - it would be a profound
breakthrough."
Dr Venter said the technology could lead to custom microbes that have myriad
practical and commercial implications such as to clean up toxic messes or to
create renewable energy by splitting water into hydrogen and oxygen.
M. genitalium image by Frantz, Albay and Bott from University of North
Carolina, Chapel Hill