Science Magazine published a paper last week, “Design and synthesis of a minimal bacterial genome,” describing the creation of a bacterium with a stripped-down genome. The paper represents twenty years of work by many scientists, including celebrated biochemist J. Craig Venter. They managed to reduce the genome by almost half, from over 900 genes to 473, a little bit at a time. The paper has made a splash across the Internet (see, for example, articles from Associated Press and Bloomberg).
Why on earth would the researchers do such a thing? The hope is that this minimal bacterium will provide a useful vehicle for future synthetic biology, enabling the production of useful medicines to treat disease.
But there is another reason they spent twenty years on this project. It’s an attempt to answer a basic question. What’s the minimum amount of genetic information needed to get a functioning cell? Estimates have ranged from 250 to 300 genes, depending on what kind of cell and where it is living. For the bacterium M. mycoides, the starting point of their work, the answer seems to be about 470 genes. Scientists want to know the answer because the simplified cell may allow them to tease apart how the genes interact, and what all of them do. It’s easier to tackle 400 genes than over 900, or in the case of the common bacterium E. coli, over 4,000.
This work has already yielded some interesting results. They still don’t know what 30 percent of the reduced genome does, just that the genes are essential. Second, genes that appear to be nonessential by themselves can become essential when another gene is deleted. Clearly there are complex interactions going on among the 473 genes.
All of this leads to an obvious question. This little bacterium has to be able to copy its DNA, transcribe and translate it into protein, plus be able to coordinate all the steps involved in cell division. It has to be able to make all the things it can’t get from its environment. That’s a lot of information to be stored and used appropriately. Hence 473 genes.