Craig Venter and his team have taken a large step in synthetic biology: They have created a full bacterial chromosome starting from a computer model of the chromosome! Enter, Mycoplasma mycoides JCVI-syn1.0.
The chromosome was slightly modified to demonstrate the technique, and inserted into an existing bacterial cell. The new chromosome is operating normally, effectively transforming the existing bacterial cell into a (slightly) modified species! This technique should be general, and useful in extending the existing recombinant DNA toolkit.
In 1995, Venter and his group determined the full sequence of Mycoplasma genitalium, chosen because it has a very small genome. They subsequently removed genes that were non-essential for viability, identifying a gene sequence they described as minimal for life, reinserting that modified chromosome back into M. genitalium, which was indeed viable. In 2007, his team transplanted a chromosome from M. mycoides to M. capricolum, which was viable, and was found to have the characteristics of M. mycoides. In 2008, his team successfully synthesized a full chromosome for M. genitalium and cloned it.
Using these techniques, a full chromosome for M. mycoides was manufactured, using a slightly modified DNA sequence that included ‘watermarks’, stretches of non-coding DNA that had literary quotes and the like encoded. The genome assembly was done using ‘sequence cassettes’ of 1,080 base pairs which had 80 bp overlaps. Yeast cells were used to assemble the cassettes into a full chromosome, in several steps. The full-assembled chromosome was extracted from the yeast cells, and introduced into M. capricolum cells that had been engineered to be restriction deficient, so they would not break down foreign DNA. The new DNA began to be expressed, and began to produce its own restriction enzymes, which recognized the M. capricolum DNA as foreign, and degraded it, effectively transforming an M. capricolum into a modified M. mycoides!
Venter is also working on synthetic blue-green bacteria that can produce biofuels from sunlight and CO2; his newly demonstrated technique will be applied to this project as well.