London, Jan 25 : Scientists have taken a crucial step forward in the creation of entirely synthetic life forms, by crafting a bacterial genome from scratch.
The research team at the J. Craig Venter Institute in Rockville, Maryland, accomplished the feat by making DNA fragments from lab chemicals and then assembling them inside a cell.
The synthetic genome contains all the instructions that an organism, in this study, a tiny bacterium called Mycoplasma genitalium, needs to live and reproduce.
The genome for the pathogenic bacterium Mycoplasma genitalium, which was made in the laboratory by Hamilton Smith and his colleagues, has 582,970 of the fundamental building blocks of DNA, called nucleotide bases, making it more than a factor of ten longer than the previous-longest stretch of genetic material created by chemical means.
The team, which includes the institute's founder, genomics pioneer Craig Venter, is now working on the final step to create life: transplanting the synthetic DNA into a cell in the hope that it will "boot up" the cell and take control of its growth and reproduction.
Smith and his colleagues started by building long strands of DNA, each a copy of about a quarter of the whole M genitalium genome. These were inserted into yeast cells, which stitched together the strands to make clones of the whole genome, named M genitalium JCVI-1.0.
The next step is to insert the synthetic chromosome into a cell, so that it can reproduce and become a new life form.
Venter's team has already demonstrated that transplanting the genome of one type of bacterium into the cell of another can change the cell's species, a process his team will now use with the new synthetic chromosome.
Smith said that producing the artificial genome was like finishing the operating system of a computer.
"By itself, it doesn't do anything, but when you install it on a computer, then you have a working computer system. It's the same with the genome: the genome is the operating system for a cell and the cytoplasm is the hardware that's required to run that genome," Nature quoted him, as saying.
M. genitalium has the smallest genome known of any organism that can grow and replicate independently. Its DNA contains the instructions for making just 485 proteins, which orchestrate the cells' functions.
Its small genome makes M. genitalium a candidate for the basis of a 'minimal organism', which would contain the bare minimum of genes needed to survive. The Venter institute team thinks that around 100 of the bacterium's genes aren't strictly necessary for life, but they don't know which 100.
The team hopes that a stripped-down version of the M. genitalium genome might serve as a general-purpose chassis to which might be added all sorts of useful designer functions, such as genes that turn the bacteria into biological factories for making carbon-based 'green' fuels or hydrogen when fed with nutrients.
The next step towards that goal is to build potential minimal genomes from scratch, transplant them into Mycoplasma, and see whether the cells survive.
"We plan to start removing putative 'non-essential' genes and test whether we get viable transplants," said Smith.
The study is published in the journal Science.