Life requires a minimum of 473 genes, scientists experimenting with artificially created genomes have shown.
The research is a step on from ground-breaking work published in 2010 in which the same US team produced the first replicating microbe containing a genetic code that had been put together in a laboratory.
Now the scientists, co-led by pioneering geneticist Professor Craig Venter, have achieved their ultimate objective - to create a minimal cell containing only the genes necessary to sustain life in its simplest form.
As before, they used Mycoplasma, a bacterium possessing the smallest known genome of any self-replicating cell.
The scientists once again created a synthetic genome, inserted into Mycoplasma, but then set about disrupting the functions of various genes.
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Eventually they whittled the genes down to the smallest number that appeared to be necessary for autonomously replicating life - 473.
The resulting genome, known as JCVI-syn3.0, could become a versatile tool for investigating core life functions.
The research, based at the J Craig Venter Institute in La Jolla, California, is published in the latest issue of the journal Science.
British expert Dr Vitor Pinheiro, lecturer in synthetic biology at University College London, described the work as a "remarkable tour de force".
He added: "The research started with a simple organism ... and removed DNA sequences that were identified as unnecessary for growth in the standardised culture conditions being used.
"It shows that despite our efforts, there are still aspects of biology we don't understand, exemplified by the 65 genes (nearly 14 per cent) that have no known function."
Professor Paul Freemont, head of molecular biosciences at Imperial College London, said: "One of the main goals of synthetic biology is to develop technologies and protocols to allow the construction of new biological cells and systems at the genetic level.
"This paper contributes a next step in the evolution of such techniques in enabling genome construction from synthetic DNA."
